diff --git a/README.md b/README.md
index eaf4779ab..f50b62380 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 Comprehensive Python Cheatsheet
 ===============================
-<sup>[Download text file](https://raw.githubusercontent.com/gto76/python-cheatsheet/main/README.md), [Buy PDF](https://transactions.sendowl.com/products/78175486/4422834F/view), [Fork me on GitHub](https://github.com/gto76/python-cheatsheet) or [Check out FAQ](https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions).
+<sup>[Download text file](https://raw.githubusercontent.com/gto76/python-cheatsheet/main/README.md), [Fork me on GitHub](https://github.com/gto76/python-cheatsheet) or [Check out FAQ](https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions).
 </sup>
 
 ![Monty Python](web/image_888.jpeg)
@@ -10,11 +10,11 @@ Contents
 --------
 **&nbsp;&nbsp;&nbsp;** **1. Collections:** **&nbsp;** **[`List`](#list)**__,__ **[`Dictionary`](#dictionary)**__,__ **[`Set`](#set)**__,__ **[`Tuple`](#tuple)**__,__ **[`Range`](#range)**__,__ **[`Enumerate`](#enumerate)**__,__ **[`Iterator`](#iterator)**__,__ **[`Generator`](#generator)**__.__  
 **&nbsp;&nbsp;&nbsp;** **2. Types:** **&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**  **[`Type`](#type)**__,__ **[`String`](#string)**__,__ **[`Regular_Exp`](#regex)**__,__ **[`Format`](#format)**__,__ **[`Numbers`](#numbers-1)**__,__ **[`Combinatorics`](#combinatorics)**__,__ **[`Datetime`](#datetime)**__.__  
-**&nbsp;&nbsp;&nbsp;** **3. Syntax:** **&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**  **[`Args`](#arguments)**__,__ **[`Inline`](#inline)**__,__ **[`Import`](#imports)**__,__ **[`Decorator`](#decorator)**__,__ **[`Class`](#class)**__,__ **[`Duck_Types`](#duck-types)**__,__ **[`Enum`](#enum)**__,__ **[`Exception`](#exceptions)**__.__  
+**&nbsp;&nbsp;&nbsp;** **3. Syntax:** **&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**  **[`Function`](#function)**__,__ **[`Inline`](#inline)**__,__ **[`Import`](#imports)**__,__ **[`Decorator`](#decorator)**__,__ **[`Class`](#class)**__,__ **[`Duck_Type`](#duck-types)**__,__ **[`Enum`](#enum)**__,__ **[`Except`](#exceptions)**__.__  
 **&nbsp;&nbsp;&nbsp;** **4. System:** **&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**  **[`Exit`](#exit)**__,__ **[`Print`](#print)**__,__ **[`Input`](#input)**__,__ **[`Command_Line_Arguments`](#command-line-arguments)**__,__ **[`Open`](#open)**__,__ **[`Path`](#paths)**__,__ **[`OS_Commands`](#os-commands)**__.__  
 **&nbsp;&nbsp;&nbsp;** **5. Data:** **&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**  **[`JSON`](#json)**__,__ **[`Pickle`](#pickle)**__,__ **[`CSV`](#csv)**__,__ **[`SQLite`](#sqlite)**__,__ **[`Bytes`](#bytes)**__,__ **[`Struct`](#struct)**__,__ **[`Array`](#array)**__,__ **[`Memory_View`](#memory-view)**__,__ **[`Deque`](#deque)**__.__  
-**&nbsp;&nbsp;&nbsp;** **6. Advanced:** **&nbsp;&nbsp;&nbsp;**  **[`Threading`](#threading)**__,__ **[`Operator`](#operator)**__,__ **[`Match_Stmt`](#match-statement)**__,__ **[`Logging`](#logging)**__,__ **[`Introspection`](#introspection)**__,__ **[`Coroutines`](#coroutines)**__.__  
-**&nbsp;&nbsp;&nbsp;** **7. Libraries:** **&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**  **[`Progress_Bar`](#progress-bar)**__,__ **[`Plot`](#plot)**__,__ **[`Table`](#table)**__,__ **[`Console_App`](#console-app)**__,__ **[`GUI`](#gui-app)**__,__ **[`Scraping`](#scraping)**__,__ **[`Web`](#web)**__,__ **[`Profile`](#profiling)**__.__  
+**&nbsp;&nbsp;&nbsp;** **6. Advanced:** **&nbsp;&nbsp;&nbsp;**  **[`Operator`](#operator)**__,__ **[`Match_Stmt`](#match-statement)**__,__ **[`Logging`](#logging)**__,__ **[`Introspection`](#introspection)**__,__ **[`Threading`](#threading)**__,__ **[`Coroutines`](#coroutines)**__.__  
+**&nbsp;&nbsp;&nbsp;** **7. Libraries:** **&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**  **[`Progress_Bar`](#progress-bar)**__,__ **[`Plot`](#plot)**__,__ **[`Table`](#table)**__,__ **[`Console_App`](#console-app)**__,__ **[`GUI`](#gui-app)**__,__ **[`Scraping`](#scraping)**__,__ **[`Web`](#web-app)**__,__ **[`Profile`](#profiling)**__.__  
 **&nbsp;&nbsp;&nbsp;** **8. Multimedia:** **&nbsp;&nbsp;**  **[`NumPy`](#numpy)**__,__ **[`Image`](#image)**__,__ **[`Animation`](#animation)**__,__ **[`Audio`](#audio)**__,__ **[`Synthesizer`](#synthesizer)**__,__ **[`Pygame`](#pygame)**__,__ **[`Pandas`](#pandas)**__,__ **[`Plotly`](#plotly)**__.__
 
 
@@ -29,7 +29,7 @@ if __name__ == '__main__':      # Skips next line if file was imported.
 List
 ----
 ```python
-<list> = [<el_1>, <el_2>, ...]  # Creates new list. Also list(<collection>).
+<list> = [<el_1>, <el_2>, ...]  # Creates a list object. Also list(<collection>).
 ```
 
 ```python
@@ -43,32 +43,35 @@ List
 ```
 
 ```python
-<list>.sort()                   # Sorts elements in ascending order.
-<list>.reverse()                # Reverses the list in-place.
-<list> = sorted(<collection>)   # Returns new list with sorted elements.
+<list>.sort()                   # Sorts the elements in ascending order.
+<list>.reverse()                # Reverses the order of list's elements.
+<list> = sorted(<collection>)   # Returns a new list with sorted elements.
 <iter> = reversed(<list>)       # Returns reversed iterator of elements.
 ```
 
 ```python
-sum_of_elements  = sum(<collection>)
+<el>  = max(<collection>)       # Returns largest element. Also min(<el_1>, ...).
+<num> = sum(<collection>)       # Returns sum of elements. Also math.prod(<coll>).
+```
+
+```python
 elementwise_sum  = [sum(pair) for pair in zip(list_a, list_b)]
 sorted_by_second = sorted(<collection>, key=lambda el: el[1])
 sorted_by_both   = sorted(<collection>, key=lambda el: (el[1], el[0]))
 flatter_list     = list(itertools.chain.from_iterable(<list>))
-product_of_elems = functools.reduce(lambda out, el: out * el, <collection>)
-list_of_chars    = list(<str>)
 ```
-* **For details about sorted(), min() and max() see [sortable](#sortable).**
-* **Module [operator](#operator) provides functions itemgetter() and mul() that offer the same functionality as [lambda](#lambda) expressions above.**
+* **For details about sort(), sorted(), min() and max() see [Sortable](#sortable).**
+* **Module [operator](#operator) has function itemgetter() that can replace listed [lambdas](#lambda).**
+* **This text uses the term collection instead of iterable. For rationale see [Collection](#collection).**
 
 ```python
-<int> = len(<list>)             # Returns number of items. Also works on other collections.
+<int> = len(<list>)             # Returns number of items. Also works on dict, set and string.
 <int> = <list>.count(<el>)      # Returns number of occurrences. Also `if <el> in <coll>: ...`.
 <int> = <list>.index(<el>)      # Returns index of the first occurrence or raises ValueError.
 <el>  = <list>.pop()            # Removes and returns item from the end or at index if passed.
-<list>.insert(<int>, <el>)      # Inserts item at index and moves the rest to the right.
+<list>.insert(<int>, <el>)      # Inserts item at passed index and moves the rest to the right.
 <list>.remove(<el>)             # Removes first occurrence of the item or raises ValueError.
-<list>.clear()                  # Removes all items. Also works on dictionary and set.
+<list>.clear()                  # Removes all list's items. Also works on dictionary and set.
 ```
 
 
@@ -79,13 +82,13 @@ Dictionary
 ```
 
 ```python
-<view> = <dict>.keys()                          # Coll. of keys that reflects changes.
-<view> = <dict>.values()                        # Coll. of values that reflects changes.
+<view> = <dict>.keys()                          # Collection of keys that reflects changes.
+<view> = <dict>.values()                        # Collection of values that reflects changes.
 <view> = <dict>.items()                         # Coll. of key-value tuples that reflects chgs.
 ```
 
 ```python
-value  = <dict>.get(key, default=None)          # Returns default if key is missing.
+value  = <dict>.get(key, default=None)          # Returns default argument if key is missing.
 value  = <dict>.setdefault(key, default=None)   # Returns and writes default if key is missing.
 <dict> = collections.defaultdict(<type>)        # Returns a dict with default value `<type>()`.
 <dict> = collections.defaultdict(lambda: 1)     # Returns a dict with default value 1.
@@ -101,7 +104,7 @@ value  = <dict>.setdefault(key, default=None)   # Returns and writes default if
 <dict>.update(<dict>)                           # Adds items. Replaces ones with matching keys.
 value = <dict>.pop(key)                         # Removes item or raises KeyError if missing.
 {k for k, v in <dict>.items() if v == value}    # Returns set of keys that point to the value.
-{k: v for k, v in <dict>.items() if k in keys}  # Filters the dictionary by keys.
+{k: v for k, v in <dict>.items() if k in keys}  # Filters the dictionary by specified keys.
 ```
 
 ### Counter
@@ -162,14 +165,11 @@ Tuple
 ```python
 >>> from collections import namedtuple
 >>> Point = namedtuple('Point', 'x y')
->>> p = Point(1, y=2); p
+>>> p = Point(1, y=2)
+>>> print(p)
 Point(x=1, y=2)
->>> p[0]
-1
->>> p.x
-1
->>> getattr(p, 'y')
-2
+>>> p.x, p[1]
+(1, 2)
 ```
 
 
@@ -177,9 +177,9 @@ Range
 -----
 **Immutable and hashable sequence of integers.**
 ```python
-<range> = range(stop)                      # range(to_exclusive)
-<range> = range(start, stop)               # range(from_inclusive, to_exclusive)
-<range> = range(start, stop, ±step)        # range(from_inclusive, to_exclusive, ±step_size)
+<range> = range(stop)                      # I.e. range(to_exclusive).
+<range> = range(start, stop)               # I.e. range(from_inclusive, to_exclusive).
+<range> = range(start, stop, ±step)        # I.e. range(from_inclusive, to_exclusive, ±step).
 ```
 
 ```python
@@ -198,6 +198,8 @@ for i, el in enumerate(<coll>, start=0):   # Returns next element and its index
 
 Iterator
 --------
+**Potentially endless stream of elements.**
+
 ```python
 <iter> = iter(<collection>)                # `iter(<iter>)` returns unmodified iterator.
 <iter> = iter(<function>, to_exclusive)    # A sequence of return values until 'to_exclusive'.
@@ -213,11 +215,11 @@ import itertools as it
 ```python
 <iter> = it.count(start=0, step=1)         # Returns updated value endlessly. Accepts floats.
 <iter> = it.repeat(<el> [, times])         # Returns element endlessly or 'times' times.
-<iter> = it.cycle(<collection>)            # Repeats the sequence endlessly.
+<iter> = it.cycle(<collection>)            # Repeats the passed sequence of elements endlessly.
 ```
 
 ```python
-<iter> = it.chain(<coll>, <coll> [, ...])  # Empties collections in order (figuratively).
+<iter> = it.chain(<coll>, <coll> [, ...])  # Empties collections in order (only figuratively).
 <iter> = it.chain.from_iterable(<coll>)    # Empties collections inside a collection in order.
 ```
 
@@ -316,27 +318,27 @@ String
 
 ```python
 <list> = <str>.split()                       # Splits on one or more whitespace characters.
-<list> = <str>.split(sep=None, maxsplit=-1)  # Splits on 'sep' str at most 'maxsplit' times.
+<list> = <str>.split(sep=None, maxsplit=-1)  # Splits on 'sep' string at most 'maxsplit' times.
 <list> = <str>.splitlines(keepends=False)    # On [\n\r\f\v\x1c-\x1e\x85\u2028\u2029] and \r\n.
-<str>  = <str>.join(<coll_of_strings>)       # Joins elements using string as a separator.
+<str>  = <str>.join(<coll_of_strings>)       # Joins elements by using string as a separator.
 ```
 
 ```python
 <bool> = <sub_str> in <str>                  # Checks if string contains the substring.
 <bool> = <str>.startswith(<sub_str>)         # Pass tuple of strings for multiple options.
 <int>  = <str>.find(<sub_str>)               # Returns start index of the first match or -1.
-<int>  = <str>.index(<sub_str>)              # Same, but raises ValueError if there's no match.
 ```
 
 ```python
-<str>  = <str>.lower()                       # Changes the case. Also upper/capitalize/title().
+<str>  = <str>.lower()                       # Lowers the case. Also upper/capitalize/title().
+<str>  = <str>.casefold()                    # Same, but converts ẞ/ß to ss, Σ/ς to σ, etc.
 <str>  = <str>.replace(old, new [, count])   # Replaces 'old' with 'new' at most 'count' times.
 <str>  = <str>.translate(<table>)            # Use `str.maketrans(<dict>)` to generate table.
 ```
 
 ```python
-<str>  = chr(<int>)                          # Converts int to Unicode character.
-<int>  = ord(<str>)                          # Converts Unicode character to int.
+<str>  = chr(<int>)                          # Converts passed integer to Unicode character.
+<int>  = ord(<str>)                          # Converts passed Unicode character to integer.
 ```
 * **Use `'unicodedata.normalize("NFC", <str>)'` on strings like `'Motörhead'` before comparing them to other strings, because `'ö'` can be stored as one or two characters.**
 * **`'NFC'` converts such characters to a single character, while `'NFD'` converts them to two.**
@@ -348,7 +350,7 @@ String
 <bool> = <str>.isnumeric()                   # Checks for [¼½¾…], [零〇一…] and isdigit().
 <bool> = <str>.isalnum()                     # Checks for [a-zA-Z…] and isnumeric().
 <bool> = <str>.isprintable()                 # Checks for [ !#$%…] and isalnum().
-<bool> = <str>.isspace()                     # Checks for [ \t\n\r\f\v\x1c-\x1f\x85\xa0…].
+<bool> = <str>.isspace()                     # Checks for [ \t\n\r\f\v\x1c-\x1f\x85…].
 ```
 
 
@@ -359,7 +361,7 @@ Regex
 ```python
 import re
 <str>   = re.sub(r'<regex>', new, text, count=0)  # Substitutes all occurrences with 'new'.
-<list>  = re.findall(r'<regex>', text)            # Returns all occurrences as strings.
+<list>  = re.findall(r'<regex>', text)            # Returns all occurrences of the pattern.
 <list>  = re.split(r'<regex>', text, maxsplit=0)  # Add brackets around regex to keep matches.
 <Match> = re.search(r'<regex>', text)             # First occurrence of the pattern or None.
 <Match> = re.match(r'<regex>', text)              # Searches only at the beginning of the text.
@@ -368,18 +370,18 @@ import re
 
 * **Raw string literals do not interpret escape sequences, thus enabling us to use regex-specific escape sequences that cause SyntaxWarning in normal string literals (since 3.12).**
 * **Argument 'new' of re.sub() can be a function that accepts Match object and returns a str.**
-* **Argument `'flags=re.IGNORECASE'` can be used with all functions.**
+* **Argument `'flags=re.IGNORECASE'` can be used with all functions that are listed above.**
 * **Argument `'flags=re.MULTILINE'` makes `'^'` and `'$'` match the start/end of each line.**
-* **Argument `'flags=re.DOTALL'` makes `'.'` also accept the `'\n'`.**
-* **`'re.compile(<regex>)'` returns a Pattern object with methods sub(), findall(), …**
+* **Argument `'flags=re.DOTALL'` makes `'.'` also accept the `'\n'` (besides all other chars).**
+* **`'re.compile(<regex>)'` returns a Pattern object with methods sub(), findall(), etc.**
 
 ### Match Object
 ```python
 <str>   = <Match>.group()                         # Returns the whole match. Also group(0).
 <str>   = <Match>.group(1)                        # Returns part inside the first brackets.
-<tuple> = <Match>.groups()                        # Returns all bracketed parts.
-<int>   = <Match>.start()                         # Returns start index of the match.
-<int>   = <Match>.end()                           # Returns exclusive end index of the match.
+<tuple> = <Match>.groups()                        # Returns all bracketed parts as strings.
+<int>   = <Match>.start()                         # Returns start index of the whole match.
+<int>   = <Match>.end()                           # Returns its exclusive end index.
 ```
 
 ### Special Sequences
@@ -388,17 +390,15 @@ import re
 '\w' == '[a-zA-Z0-9_]'                            # Also [ª²³…]. Matches an alphanumeric or _.
 '\s' == '[ \t\n\r\f\v]'                           # Also [\x1c-\x1f…]. Matches a whitespace.
 ```
-
-* **By default, decimal characters, alphanumerics and whitespaces from all alphabets are matched unless `'flags=re.ASCII'` argument is used.**
-* **It restricts special sequence matches to `'[\x00-\x7f]'` (the first 128 characters) and also prevents `'\s'` from accepting `'[\x1c-\x1f]'` (file, table, row, and field separators).**
+* **By default, decimal characters and alphanumerics from all alphabets are matched unless `'flags=re.ASCII'` is used. It restricts special sequence matches to the first 128 Unicode characters and also prevents `'\s'` from accepting `'\x1c'`, `'\x1d'`, `'\x1e'` and `'\x1f'` (non-printable characters that divide text into files, tables, rows and fields, respectively).**
 * **Use a capital letter for negation (all non-ASCII characters will be matched when used in combination with ASCII flag).**
 
 
 Format
 ------
 ```perl
-<str> = f'{<el_1>}, {<el_2>}'            # Curly brackets can also contain expressions.
-<str> = '{}, {}'.format(<el_1>, <el_2>)  # Or: '{0}, {a}'.format(<el_1>, a=<el_2>)
+<str> = f'{<el_1>}, {<el_2>}'            # Curly braces can also contain expressions.
+<str> = '{}, {}'.format(<el_1>, <el_2>)  # Same as '{0}, {a}'.format(<el_1>, a=<el_2>).
 <str> = '%s, %s' % (<el_1>, <el_2>)      # Redundant and inferior C-style formatting.
 ```
 
@@ -418,8 +418,8 @@ Format
 {<el>:.<10}                              # '<el>......'
 {<el>:0}                                 # '<el>'
 ```
-* **Objects are rendered using `'format(<el>, "<options>")'`.**
-* **Options can be generated dynamically: `f'{<el>:{<str/int>}[…]}'`.**
+* **Objects are rendered by calling the `'format(<el>, "<options>")'` function.**
+* **Options inside curly braces can be generated dynamically: `f'{<el>:{<str/int>}[…]}'`.**
 * **Adding `'='` to the expression prepends it to the output: `f'{1+1=}'` returns `'1+1=2'`.**
 * **Adding `'!r'` to the expression converts object to string by calling its [repr()](#class) method.**
 
@@ -485,67 +485,77 @@ Format
 ### Ints
 ```python
 {90:c}                                   # 'Z'. Unicode character with value 90.
-{90:b}                                   # '1011010'. Number 90 in binary.
-{90:X}                                   # '5A'. Number 90 in uppercase hexadecimal.
+{90:b}                                   # '1011010'. Binary representation of the int.
+{90:X}                                   # '5A'. Hexadecimal with upper-case letters.
 ```
 
 
 Numbers
 -------
 ```python
-<int>      = int(<float/str/bool>)                # Or: math.floor(<float>)
-<float>    = float(<int/str/bool>)                # Or: <int/float>e±<int>
-<complex>  = complex(real=0, imag=0)              # Or: <int/float> ± <int/float>j
-<Fraction> = fractions.Fraction(0, 1)             # Or: Fraction(numerator=0, denominator=1)
-<Decimal>  = decimal.Decimal(<str/int>)           # Or: Decimal((sign, digits, exponent))
+<int>      = int(<float/str/bool>)             # Whole number of any size. Truncates floats.
+<float>    = float(<int/str/bool>)             # 64-bit decimal number. Also <float>e±<int>.
+<complex>  = complex(real=0, imag=0)           # A complex number. Also `<float> ± <float>j`.
+<Fraction> = fractions.Fraction(<int>, <int>)  # E.g. `Fraction(1, 2) / 3 == Fraction(1, 6)`.
+<Decimal>  = decimal.Decimal(<str/int/tuple>)  # E.g. `Decimal((1, (2, 3), 4)) == -230_000`.
 ```
-* **`'int(<str>)'` and `'float(<str>)'` raise ValueError on malformed strings.**
-* **Decimal numbers are stored exactly, unlike most floats where `'1.1 + 2.2 != 3.3'`.**
-* **Floats can be compared with: `'math.isclose(<float>, <float>)'`.**
+* **`'int(<str>)'` and `'float(<str>)'` raise ValueError if passed string is malformed.**
+* **Decimal objects store numbers exactly, unlike most floats where `'1.1 + 2.2 != 3.3'`.**
+* **Floats can be compared with: `'math.isclose(<float>, <float>, rel_tol=1e-09)'`.**
 * **Precision of decimal operations is set with: `'decimal.getcontext().prec = <int>'`.**
+* **Bools can be used anywhere ints can, because bool is a subclass of int: `'True + 1 == 2'`.**
 
-### Basic Functions
+### Built-in Functions
 ```python
-<num> = pow(<num>, <num>)                         # Or: <number> ** <number>
-<num> = abs(<num>)                                # <float> = abs(<complex>)
-<num> = round(<num> [, ±ndigits])                 # `round(126, -1) == 130`
+<num> = pow(<num>, <num>)                      # E.g. `pow(2, 3) == 2 ** 3 == 8`.
+<num> = abs(<num>)                             # E.g. `abs(complex(3, 4)) == 5`.
+<num> = round(<num> [, ±ndigits])              # E.g. `round(123, -1) == 120`.
+<num> = min(<collection>)                      # Also max(<num>, <num> [, ...]).
+<num> = sum(<collection>)                      # Also math.prod(<collection>).
 ```
 
 ### Math
 ```python
-from math import e, pi, inf, nan, isinf, isnan    # `<el> == nan` is always False.
-from math import sin, cos, tan, asin, acos, atan  # Also: degrees, radians.
-from math import log, log10, log2                 # Log can accept base as second arg.
+from math import floor, ceil, trunc            # They convert floats into integers.
+from math import pi, inf, nan, isnan           # `inf * 0` and `nan + 1` return nan.
+from math import sqrt, factorial               # `sqrt(-1)` will raise ValueError.
+from math import sin, cos, tan                 # Also: asin, acos, degrees, radians.
+from math import log, log10, log2              # Log accepts base as second argument.
 ```
 
 ### Statistics
 ```python
-from statistics import mean, median, variance     # Also: stdev, quantiles, groupby.
+from statistics import mean, median, mode      # Mode returns the most common item.
+from statistics import variance, stdev         # Also: pvariance, pstdev, quantiles.
 ```
 
 ### Random
 ```python
-from random import random, randint, choice        # Also: shuffle, gauss, triangular, seed.
-<float> = random()                                # A float inside [0, 1).
-<int>   = randint(from_inc, to_inc)               # An int inside [from_inc, to_inc].
-<el>    = choice(<sequence>)                      # Keeps the sequence intact.
+from random import random, randint, uniform    # Also: gauss, choice, shuffle, seed.
 ```
 
-### Bin, Hex
 ```python
-<int> = ±0b<bin>                                  # Or: ±0x<hex>
-<int> = int('±<bin>', 2)                          # Or: int('±<hex>', 16)
-<int> = int('±0b<bin>', 0)                        # Or: int('±0x<hex>', 0)
-<str> = bin(<int>)                                # Returns '[-]0b<bin>'. Also hex().
+<float> = random()                             # Returns a float inside [0, 1).
+<num>   = randint/uniform(a, b)                # Returns an int/float inside [a, b].
+<float> = gauss(mean, stdev)                   # Also triangular(low, high, mode).
+<el>    = choice(<sequence>)                   # Keeps it intact. Also sample(p, n).
+shuffle(<list>)                                # Works on all mutable sequences.
+```
+
+### Hexadecimal Numbers
+```python
+<int> = 0x<hex>                                # E.g. `0xFF == 255`. Also 0b<bin>.
+<int> = int('±<hex>', 16)                      # Also int('±0x<hex>/±0b<bin>', 0).
+<str> = hex(<int>)                             # Returns '[-]0x<hex>'. Also bin().
 ```
 
 ### Bitwise Operators
 ```python
-<int> = <int> & <int>                             # And (0b1100 & 0b1010 == 0b1000).
-<int> = <int> | <int>                             # Or  (0b1100 | 0b1010 == 0b1110).
-<int> = <int> ^ <int>                             # Xor (0b1100 ^ 0b1010 == 0b0110).
-<int> = <int> << n_bits                           # Left shift. Use >> for right.
-<int> = ~<int>                                    # Not. Also -<int> - 1.
+<int> = <int> & <int>                          # E.g. `0b1100 & 0b1010 == 0b1000`.
+<int> = <int> | <int>                          # E.g. `0b1100 | 0b1010 == 0b1110`.
+<int> = <int> ^ <int>                          # E.g. `0b1100 ^ 0b1010 == 0b0110`.
+<int> = <int> << n_bits                        # E.g. `0b1111 << 4 == 0b11110000`.
+<int> = ~<int>                                 # E.g. `~0b1 == -0b10 == -(0b1+1)`.
 ```
 
 
@@ -556,36 +566,24 @@ import itertools as it
 ```
 
 ```python
->>> list(it.product([0, 1], repeat=3))
-[(0, 0, 0), (0, 0, 1), (0, 1, 0), (0, 1, 1),
- (1, 0, 0), (1, 0, 1), (1, 1, 0), (1, 1, 1)]
-```
-
-```python
->>> list(it.product('abc', 'abc'))                    #   a  b  c
-[('a', 'a'), ('a', 'b'), ('a', 'c'),                  # a x  x  x
- ('b', 'a'), ('b', 'b'), ('b', 'c'),                  # b x  x  x
- ('c', 'a'), ('c', 'b'), ('c', 'c')]                  # c x  x  x
+>>> list(it.product('abc', repeat=2))        #   a  b  c
+[('a', 'a'), ('a', 'b'), ('a', 'c'),         # a x  x  x
+ ('b', 'a'), ('b', 'b'), ('b', 'c'),         # b x  x  x
+ ('c', 'a'), ('c', 'b'), ('c', 'c')]         # c x  x  x
 ```
 
 ```python
->>> list(it.combinations('abc', 2))                   #   a  b  c
-[('a', 'b'), ('a', 'c'),                              # a .  x  x
- ('b', 'c')]                                          # b .  .  x
+>>> list(it.permutations('abc', 2))          #   a  b  c
+[('a', 'b'), ('a', 'c'),                     # a .  x  x
+ ('b', 'a'), ('b', 'c'),                     # b x  .  x
+ ('c', 'a'), ('c', 'b')]                     # c x  x  .
 ```
 
 ```python
->>> list(it.combinations_with_replacement('abc', 2))  #   a  b  c
-[('a', 'a'), ('a', 'b'), ('a', 'c'),                  # a x  x  x
- ('b', 'b'), ('b', 'c'),                              # b .  x  x
- ('c', 'c')]                                          # c .  .  x
-```
-
-```python
->>> list(it.permutations('abc', 2))                   #   a  b  c
-[('a', 'b'), ('a', 'c'),                              # a .  x  x
- ('b', 'a'), ('b', 'c'),                              # b x  .  x
- ('c', 'a'), ('c', 'b')]                              # c x  x  .
+>>> list(it.combinations('abc', 2))          #   a  b  c
+[('a', 'b'), ('a', 'c'),                     # a .  x  x
+ ('b', 'c')                                  # b .  .  x
+]                                            # c .  .  .
 ```
 
 
@@ -605,10 +603,10 @@ import zoneinfo, dateutil.tz
 <DT> = datetime(year, month, day, hour=0)   # Also: `minute=0, second=0, microsecond=0, …`.
 <TD> = timedelta(weeks=0, days=0, hours=0)  # Also: `minutes=0, seconds=0, microseconds=0`.
 ```
-* **Aware `<a>` time and datetime objects have defined timezone, while naive `<n>` don't. If object is naive, it is presumed to be in the system's timezone!**
-* **`'fold=1'` means the second pass in case of time jumping back for one hour.**
+* **Times and datetimes that have defined timezone are called aware and ones that don't, naive. If time or datetime object is naive, it is presumed to be in the system's timezone!**
+* **`'fold=1'` means the second pass in case of time jumping back (usually for one hour).**
 * **Timedelta normalizes arguments to ±days, seconds (< 86 400) and microseconds (< 1M). Its str() method returns `'[±D, ]H:MM:SS[.…]'` and total_seconds() a float of all seconds.**
-* **Use `'<D/DT>.weekday()'` to get the day of the week as an int, with Monday being 0.**
+* **Use `'<D/DT>.weekday()'` to get the day of the week as an integer, with Monday being 0.**
 
 ### Now
 ```python
@@ -617,10 +615,10 @@ import zoneinfo, dateutil.tz
 ```
 * **To extract time use `'<DTn>.time()'`, `'<DTa>.time()'` or `'<DTa>.timetz()'`.**
 
-### Timezone
+### Timezones
 ```python
-<tzinfo> = timezone.utc                     # London without daylight saving time (DST).
-<tzinfo> = timezone(<timedelta>)            # Timezone with fixed offset from UTC.
+<tzinfo> = timezone.utc                     # Coordinated universal time (UK without DST).
+<tzinfo> = timezone(<timedelta>)            # Timezone with fixed offset from universal time.
 <tzinfo> = dateutil.tz.tzlocal()            # Local timezone with dynamic offset from UTC.
 <tzinfo> = zoneinfo.ZoneInfo('<iana_key>')  # 'Continent/City_Name' zone with dynamic offset.
 <DTa>    = <DT>.astimezone([<tzinfo>])      # Converts DT to the passed or local fixed zone.
@@ -632,7 +630,7 @@ import zoneinfo, dateutil.tz
 ### Encode
 ```python
 <D/T/DT> = D/T/DT.fromisoformat(<str>)      # Object from ISO string. Raises ValueError.
-<DT>     = DT.strptime(<str>, '<format>')   # Datetime from str, according to format.
+<DT>     = DT.strptime(<str>, '<format>')   # Datetime from custom string. See Format.
 <D/DTn>  = D/DT.fromordinal(<int>)          # D/DT from days since the Gregorian NYE 1.
 <DTn>    = DT.fromtimestamp(<float>)        # Local naive DT from seconds since the Epoch.
 <DTa>    = DT.fromtimestamp(<float>, <tz>)  # Aware datetime from seconds since the Epoch.
@@ -642,9 +640,9 @@ import zoneinfo, dateutil.tz
 
 ### Decode
 ```python
-<str>    = <D/T/DT>.isoformat(sep='T')      # Also `timespec='auto/hours/minutes/seconds/…'`.
+<str>    = <D/T/DT>.isoformat(sep='T')      # Also `timespec='auto/hours/minutes/seconds…'`.
 <str>    = <D/T/DT>.strftime('<format>')    # Custom string representation of the object.
-<int>    = <D/DT>.toordinal()               # Days since Gregorian NYE 1, ignoring time and tz.
+<int>    = <D/DT>.toordinal()               # Days since NYE 1. Ignores DT's time and zone.
 <float>  = <DTn>.timestamp()                # Seconds since the Epoch, from local naive DT.
 <float>  = <DTa>.timestamp()                # Seconds since the Epoch, from aware datetime.
 ```
@@ -655,53 +653,53 @@ import zoneinfo, dateutil.tz
 >>> dt.strftime("%dth of %B '%y (%a), %I:%M %p %Z")
 "14th of August '25 (Thu), 11:39 PM UTC+02:00"
 ```
-* **`'%z'` accepts `'±HH[:]MM'` and returns `'±HHMM'` or empty string if datetime is naive.**
-* **`'%Z'` accepts `'UTC/GMT'` and local timezone's code and returns timezone's name, `'UTC[±HH:MM]'` if timezone is nameless, or an empty string if datetime is naive.**
+* **`'%z'` accepts `'±HH[:]MM'` and returns `'±HHMM'` or empty string if object is naive.**
+* **`'%Z'` accepts `'UTC/GMT'` and local timezone's code and returns timezone's name, `'UTC[±HH:MM]'` if timezone is nameless, or an empty string if object is naive.**
 
 ### Arithmetics
 ```python
 <bool>   = <D/T/DTn> > <D/T/DTn>            # Ignores time jumps (fold attribute). Also ==.
-<bool>   = <DTa>     > <DTa>                # Ignores jumps if they share tz object. Broken ==.
+<bool>   = <DTa>     > <DTa>                # Ignores time jumps if they share tzinfo object.
 <TD>     = <D/DTn>   - <D/DTn>              # Ignores jumps. Convert to UTC for actual delta.
-<TD>     = <DTa>     - <DTa>                # Ignores jumps if they share tzinfo object.
+<TD>     = <DTa>     - <DTa>                # Ignores jumps if they share the tzinfo object.
 <D/DT>   = <D/DT>    ± <TD>                 # Returned datetime can fall into missing hour.
-<TD>     = <TD>      * <float>              # Also: <TD> = abs(<TD>) and <TD> = <TD> ±% <TD>.
-<float>  = <TD>      / <TD>                 # E.g. how many hours are in TD. Also //, divmod().
+<TD>     = <TD>      * <float>              # Also `<TD> = abs(<TD>)`, `<TD> = <TD> ± <TD>`.
+<float>  = <TD>      / <TD>                 # Also `(<int>, <TD>) = divmod(<TD>, <TD>)`.
 ```
 
 
-Arguments
----------
-### Inside Function Call
+Function
+--------
+**Independent block of code that returns a value when called.**
 ```python
-func(<positional_args>)                           # func(0, 0)
-func(<keyword_args>)                              # func(x=0, y=0)
-func(<positional_args>, <keyword_args>)           # func(0, y=0)
+def <func_name>(<nondefault_args>): ...                  # E.g. `def func(x, y): ...`.
+def <func_name>(<default_args>): ...                     # E.g. `def func(x=0, y=0): ...`.
+def <func_name>(<nondefault_args>, <default_args>): ...  # E.g. `def func(x, y=0): ...`.
 ```
+* **Function returns None if it doesn't encounter `'return <obj/exp>'` statement.**
+* **Run `'global <var_name>'` inside the function before assigning to global variable.**
+* **Default values are evaluated when function is first encountered in the scope. Any mutation of a mutable default value will persist between invocations!**
+
+### Function Call
 
-### Inside Function Definition
 ```python
-def func(<nondefault_args>): ...                  # def func(x, y): ...
-def func(<default_args>): ...                     # def func(x=0, y=0): ...
-def func(<nondefault_args>, <default_args>): ...  # def func(x, y=0): ...
+<obj> = <function>(<positional_args>)                    # E.g. `func(0, 0)`.
+<obj> = <function>(<keyword_args>)                       # E.g. `func(x=0, y=0)`.
+<obj> = <function>(<positional_args>, <keyword_args>)    # E.g. `func(0, y=0)`.
 ```
-* **Default values are evaluated when function is first encountered in the scope.**
-* **Any mutation of a mutable default value will persist between invocations!**
 
 
 Splat Operator
 --------------
-### Inside Function Call
 **Splat expands a collection into positional arguments, while splatty-splat expands a dictionary into keyword arguments.**
 ```python
-args   = (1, 2)
-kwargs = {'x': 3, 'y': 4, 'z': 5}
+args, kwargs = (1, 2), {'z': 3}
 func(*args, **kwargs)
 ```
 
 #### Is the same as:
 ```python
-func(1, 2, x=3, y=4, z=5)
+func(1, 2, z=3)
 ```
 
 ### Inside Function Definition
@@ -716,40 +714,27 @@ def add(*a):
 6
 ```
 
-#### Legal argument combinations:
-```python
-def f(*args): ...               # f(1, 2, 3)
-def f(x, *args): ...            # f(1, 2, 3)
-def f(*args, z): ...            # f(1, 2, z=3)
-```
-
-```python
-def f(**kwargs): ...            # f(x=1, y=2, z=3)
-def f(x, **kwargs): ...         # f(x=1, y=2, z=3) | f(1, y=2, z=3)
-```
-
-```python
-def f(*args, **kwargs): ...     # f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)
-def f(x, *args, **kwargs): ...  # f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)
-def f(*args, y, **kwargs): ...  # f(x=1, y=2, z=3) | f(1, y=2, z=3)
-```
-
-```python
-def f(*, x, y, z): ...          # f(x=1, y=2, z=3)
-def f(x, *, y, z): ...          # f(x=1, y=2, z=3) | f(1, y=2, z=3)
-def f(x, y, *, z): ...          # f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3)
+#### Allowed compositions of arguments and the ways they can be called:
+```text
++---------------------------+--------------+--------------+----------------+
+|                           |  func(1, 2)  | func(1, y=2) | func(x=1, y=2) |
++---------------------------+--------------+--------------+----------------+
+| func(x, *args, **kwargs): |     yes      |     yes      |      yes       |
+| func(*args, y, **kwargs): |              |     yes      |      yes       |
+| func(*, x, **kwargs):     |              |              |      yes       |
++---------------------------+--------------+--------------+----------------+
 ```
 
 ### Other Uses
 ```python
-<list>  = [*<coll.> [, ...]]    # Or: list(<collection>) [+ ...]
-<tuple> = (*<coll.>, [...])     # Or: tuple(<collection>) [+ ...]
-<set>   = {*<coll.> [, ...]}    # Or: set(<collection>) [| ...]
-<dict>  = {**<dict> [, ...]}    # Or: <dict> | ...
+<list>  = [*<collection> [, ...]]  # Or: list(<coll>) [+ ...]
+<tuple> = (*<collection>, [...])   # Or: tuple(<coll>) [+ ...]
+<set>   = {*<collection> [, ...]}  # Or: set(<coll>) [| ...]
+<dict>  = {**<dict> [, ...]}       # Or: <dict> | ...
 ```
 
 ```python
-head, *body, tail = <coll.>     # Head or tail can be omitted.
+head, *body, tail = <collection>   # Head or tail can be omitted.
 ```
 
 
@@ -763,10 +748,10 @@ Inline
 
 ### Comprehensions
 ```python
-<list> = [i+1 for i in range(10)]                   # Or: [1, 2, ..., 10]
-<iter> = (i for i in range(10) if i > 5)            # Or: iter([6, 7, 8, 9])
-<set>  = {i+5 for i in range(10)}                   # Or: {5, 6, ..., 14}
-<dict> = {i: i*2 for i in range(10)}                # Or: {0: 0, 1: 2, ..., 9: 18}
+<list> = [i+1 for i in range(10)]                   # Returns [1, 2, ..., 10].
+<iter> = (i for i in range(10) if i > 5)            # Returns iter([6, 7, 8, 9]).
+<set>  = {i+5 for i in range(10)}                   # Returns {5, 6, ..., 14}.
+<dict> = {i: i*2 for i in range(10)}                # Returns {0: 0, 1: 2, ..., 9: 18}.
 ```
 
 ```python
@@ -780,9 +765,9 @@ from functools import reduce
 ```
 
 ```python
-<iter> = map(lambda x: x + 1, range(10))            # Or: iter([1, 2, ..., 10])
-<iter> = filter(lambda x: x > 5, range(10))         # Or: iter([6, 7, 8, 9])
-<obj>  = reduce(lambda out, x: out + x, range(10))  # Or: 45
+<iter> = map(lambda x: x + 1, range(10))            # Returns iter([1, 2, ..., 10]).
+<iter> = filter(lambda x: x > 5, range(10))         # Returns iter([6, 7, 8, 9]).
+<obj>  = reduce(lambda out, x: out + x, range(10))  # Returns 45.
 ```
 
 ### Any, All
@@ -797,24 +782,32 @@ from functools import reduce
 ```
 
 ```python
->>> [a if a else 'zero' for a in (0, 1, 2, 3)]      # `any([0, '', [], None]) == False`
+>>> [i if i else 'zero' for i in (0, 1, 2, 3)]      # `any([0, '', [], None]) == False`
 ['zero', 1, 2, 3]
 ```
 
+### And, Or
+```python
+<obj> = <exp> and <exp> [and ...]                   # Returns first false or last object.
+<obj> = <exp> or <exp> [or ...]                     # Returns first true or last object.
+```
+
+### Walrus Operator
+```python
+>>> [i for ch in '0123' if (i := int(ch)) > 0]      # Assigns to variable mid-sentence.
+[1, 2, 3]
+```
+
 ### Named Tuple, Enum, Dataclass
 ```python
 from collections import namedtuple
-Point = namedtuple('Point', 'x y')                  # Creates a tuple's subclass.
+Point = namedtuple('Point', 'x y')                  # Creates tuple's subclass.
 point = Point(0, 0)                                 # Returns its instance.
-```
 
-```python
 from enum import Enum
-Direction = Enum('Direction', 'N E S W')            # Creates an enum.
+Direction = Enum('Direction', 'N E S W')            # Creates Enum's subclass.
 direction = Direction.N                             # Returns its member.
-```
 
-```python
 from dataclasses import make_dataclass
 Player = make_dataclass('Player', ['loc', 'dir'])   # Creates a class.
 player = Player(point, direction)                   # Returns its instance.
@@ -830,16 +823,16 @@ import <module>            # Imports a built-in or '<module>.py'.
 import <package>           # Imports a built-in or '<package>/__init__.py'.
 import <package>.<module>  # Imports a built-in or '<package>/<module>.py'.
 ```
-* **Package is a collection of modules, but it can also define its own objects.**
+* **Package is a collection of modules, but it can also define its own functions, classes, etc.**
 * **On a filesystem this corresponds to a directory of Python files with an optional init script.**
-* **Running `'import <package>'` does not automatically provide access to the package's modules unless they are explicitly imported in its init script.**
+* **Running `'import <package>'` does not automatically provide access to the package's modules unless they are explicitly imported in the `'<package>/__init__.py'` script.**
 * **Directory of the file that is passed to python command serves as a root of local imports.**
 * **For relative imports use `'from .[…][<pkg/module>[.…]] import <obj>'`.**
 
 
 Closure
 -------
-**We have/get a closure in Python when a nested function references a value of its enclosing function and then the enclosing function returns the nested function.**
+**We have/get a closure in Python when a nested function references a value of its enclosing function and then the enclosing function returns its nested function.**
 
 ```python
 def get_multiplier(a):
@@ -868,8 +861,7 @@ from functools import partial
 >>> multiply_by_3(10)
 30
 ```
-* **Partial is also useful in cases when a function needs to be passed as an argument because it enables us to set its arguments beforehand.**
-* **A few examples being: `'defaultdict(<func>)'`, `'iter(<func>, to_exc)'` and dataclass's `'field(default_factory=<func>)'`.**
+* **Partial is also useful in cases when a function needs to be passed as an argument because it enables us to set its arguments beforehand (`'collections.defaultdict(<func>)'`, `'iter(<func>, to_exc)'` and `'dataclasses.field(default_factory=<func>)'`).**
 
 ### Non-Local
 **If variable is being assigned to anywhere in the scope, it is regarded as a local variable, unless it is declared as a 'global' or a 'nonlocal'.**
@@ -893,8 +885,7 @@ def get_counter():
 
 Decorator
 ---------
-* **A decorator takes a function, adds some functionality and returns it.**
-* **It can be any [callable](#callable), but is usually implemented as a function that returns a [closure](#closure).**
+**A decorator takes a function, adds some functionality and returns it. It can be any [callable](#callable), but is usually implemented as a function that returns a [closure](#closure).**
 
 ```python
 @decorator_name
@@ -931,7 +922,7 @@ from functools import cache
 def fib(n):
     return n if n < 2 else fib(n-2) + fib(n-1)
 ```
-* **Potential problem with cache is that it can grow indefinitely. To clear its stored values run `'fib.cache_clear()'`, or use `'@lru_cache(maxsize=<int>)'` decorator instead.**
+* **Potential problem with cache is that it can grow indefinitely. To clear stored values run `'<func>.cache_clear()'`, or use `'@lru_cache(maxsize=<int>)'` decorator instead.**
 * **CPython interpreter limits recursion depth to 3000 by default. To increase it run `'sys.setrecursionlimit(<int>)'`.**
 
 ### Parametrized Decorator
@@ -974,15 +965,15 @@ class MyClass:
     def get_class_name(cls):
         return cls.__name__
 ```
-* **Return value of str() should be readable and of repr() unambiguous.**
-* **If only repr() is defined, it will also be used for str().**
-* **Methods decorated with `'@staticmethod'` do not receive 'self' nor 'cls' as their first arg.**
 
 ```python
 >>> obj = MyClass(1)
 >>> obj.a, str(obj), repr(obj)
 (1, '1', 'MyClass(1)')
 ```
+* **Methods whose names start and end with two underscores are called special methods. They are executed when object is passed to a built-in function or used as an operand, for&nbsp;example, `'print(a)'` calls `'a.__str__()'` and `'a + b'` calls `'a.__add__(b)'`.**
+* **Methods decorated with `'@staticmethod'` receive neither 'self' nor 'cls' argument.**
+* **Return value of str() special method should be readable and of repr() unambiguous. If only repr() is defined, it will also be used for str().**
 
 #### Expressions that call the str() method:
 ```python
@@ -990,7 +981,6 @@ print(<obj>)
 f'{<obj>}'
 logging.warning(<obj>)
 csv.writer(<file>).writerow([<obj>])
-raise Exception(<obj>)
 ```
 
 #### Expressions that call the repr() method:
@@ -998,33 +988,34 @@ raise Exception(<obj>)
 print/str/repr([<obj>])
 print/str/repr({<obj>: <obj>})
 f'{<obj>!r}'
-Z = dataclasses.make_dataclass('Z', ['a']); print/str/repr(Z(<obj>))
->>> <obj>
+Z = make_dataclass('Z', ['a']); print/str/repr(Z(<obj>))
 ```
 
-### Inheritance
+### Subclass
+* **Inheritance is a mechanism that enables a class to extend some other class (that is, subclass to extend its parent), and by doing so inherit all of its methods and attributes.**
+* **Subclass can then add its own methods and attributes or override inherited ones by reusing their names.**
+
 ```python
 class Person:
     def __init__(self, name):
         self.name = name
+    def __repr__(self):
+        return f'Person({self.name!r})'
+    def __lt__(self, other):
+        return self.name < other.name
 
 class Employee(Person):
     def __init__(self, name, staff_num):
         super().__init__(name)
         self.staff_num = staff_num
+    def __repr__(self):
+        return f'Employee({self.name!r}, {self.staff_num})'
 ```
 
-#### Multiple inheritance:
-```python
-class A: pass
-class B: pass
-class C(A, B): pass
-```
-
-**MRO determines the order in which parent classes are traversed when searching for a method or an attribute:**
 ```python
->>> C.mro()
-[<class 'C'>, <class 'A'>, <class 'B'>, <class 'object'>]
+>>> people = {Person('Ann'), Employee('Bob', 0)}
+>>> sorted(people)
+[Person('Ann'), Employee('Bob', 0)]
 ```
 
 ### Type Annotations
@@ -1033,9 +1024,9 @@ class C(A, B): pass
 ```python
 from collections import abc
 
-<name>: <type> [| ...] [= <obj>]                              # `|` since 3.10.
-<name>: list/set/abc.Iterable/abc.Sequence[<type>] [= <obj>]  # Since 3.9.
-<name>: dict/tuple[<type>, ...] [= <obj>]                     # Since 3.9.
+<name>: <type> [| ...] [= <obj>]
+<name>: list/set/abc.Iterable/abc.Sequence[<type>] [= <obj>]
+<name>: tuple/dict[<type>, ...] [= <obj>]
 ```
 
 ### Dataclass
@@ -1051,13 +1042,13 @@ class <class_name>:
 ```
 * **Objects can be made [sortable](#sortable) with `'order=True'` and immutable with `'frozen=True'`.**
 * **For object to be [hashable](#hashable), all attributes must be hashable and 'frozen' must be True.**
-* **Function field() is needed because `'<attr_name>: list = []'` would make a list that is shared among all instances. Its 'default_factory' argument can be any [callable](#callable).**
+* **Function field() is needed because `'<attr_name>: list = []'` would make a list that is shared among all instances. Its 'default_factory' argument accepts any [callable](#callable) object.**
 * **For attributes of arbitrary type use `'typing.Any'`.**
 
 ```python
-<class> = make_dataclass('<class_name>', <coll_of_attribute_names>)
-<class> = make_dataclass('<class_name>', <coll_of_tuples>)
-<tuple> = ('<attr_name>', <type> [, <default_value>])
+P = make_dataclass('P', ['x', 'y'])
+P = make_dataclass('P', [('x', float), ('y', float)])
+P = make_dataclass('P', [('x', float, 0), ('y', float, 0)])
 ```
 
 ### Property
@@ -1081,7 +1072,7 @@ class Person:
 ```
 
 ### Slots
-**Mechanism that restricts objects to attributes listed in 'slots', reduces their memory footprint.**
+**Mechanism that restricts objects to attributes listed in 'slots'.**
 
 ```python
 class MyClassWithSlots:
@@ -1102,9 +1093,8 @@ Duck Types
 **A duck type is an implicit type that prescribes a set of special methods. Any object that has those methods defined is considered a member of that duck type.**
 
 ### Comparable
-* **If eq() method is not overridden, it returns `'id(self) == id(other)'`, which is the same as `'self is other'`.**
-* **That means all objects compare not equal by default.**
-* **Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted. False is returned if both return NotImplemented.**
+* **If eq() method is not overridden, it returns `'id(self) == id(other)'`, which is the same as `'self is other'`. That means all user-defined objects compare not equal by default (because id() returns object's memory address that is guaranteed to be unique).**
+* **Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted. Result is False if both return NotImplemented.**
 * **Ne() automatically works on any object that has eq() defined.**
 
 ```python
@@ -1118,9 +1108,8 @@ class MyComparable:
 ```
 
 ### Hashable
-* **Hashable object needs both hash() and eq() methods and its hash value should never change.**
-* **Hashable objects that compare equal must have the same hash value, meaning default hash() that returns `'id(self)'` will not do.**
-* **That is why Python automatically makes classes unhashable if you only implement eq().**
+* **Hashable object needs both hash() and eq() methods and its hash value must not change.**
+* **Hashable objects that compare equal must have the same hash value, meaning default hash() that returns `'id(self)'` will not do. That is why Python automatically makes classes unhashable if you only implement eq().**
 
 ```python
 class MyHashable:
@@ -1138,7 +1127,7 @@ class MyHashable:
 ```
 
 ### Sortable
-* **With 'total_ordering' decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods and the rest will be automatically generated.**
+* **With 'total_ordering' decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods (used by <, >, <=, >=) and the rest will be automatically generated.**
 * **Functions sorted() and min() only require lt() method, while max() only requires gt(). However, it is best to define them all so that confusion doesn't arise in other contexts.**
 * **When two lists, strings or dataclasses are compared, their values get compared in order until a pair of unequal values is found. The comparison of this two values is then returned. The shorter sequence is considered smaller in case of all values being equal.**
 * **To sort collection of strings in proper alphabetical order pass `'key=locale.strxfrm'` to sorted() after running `'locale.setlocale(locale.LC_COLLATE, "en_US.UTF-8")'`.**
@@ -1163,7 +1152,8 @@ class MySortable:
 ### Iterator
 * **Any object that has methods next() and iter() is an iterator.**
 * **Next() should return next item or raise StopIteration exception.**
-* **Iter() should return 'self'.**
+* **Iter() should return an iterator of remaining items, i.e. 'self'.**
+* **Any object that has iter() method can be used in a for loop.**
 ```python
 class Counter:
     def __init__(self):
@@ -1182,14 +1172,14 @@ class Counter:
 ```
 
 #### Python has many different iterator objects:
-* **Sequence iterators returned by the [iter()](#iterator) function, such as list\_iterator and set\_iterator.**
+* **Sequence iterators returned by the [iter()](#iterator) function, such as list\_iterator, etc.**
 * **Objects returned by the [itertools](#itertools) module, such as count, repeat and cycle.**
 * **Generators returned by the [generator functions](#generator) and [generator expressions](#comprehensions).**
 * **File objects returned by the [open()](#open) function, etc.**
 
 ### Callable
-* **All functions and classes have a call() method, hence are callable.**
-* **Use `'callable(<obj>)'` or `'isinstance(<obj>, collections.abc.Callable)'` to check if object is callable.**
+* **All functions and classes have a call() method that is executed when they are called.**
+* **Use `'callable(<obj>)'` or `'isinstance(<obj>, collections.abc.Callable)'` to check if object is callable. You can also call the object and check if it raised TypeError.**
 * **When this cheatsheet uses `'<function>'` as an argument, it means `'<callable>'`.**
 ```python
 class Counter:
@@ -1208,8 +1198,8 @@ class Counter:
 
 ### Context Manager
 * **With statements only work on objects that have enter() and exit() special methods.**
-* **Enter() should lock the resources and optionally return an object.**
-* **Exit() should release the resources.**
+* **Enter() should lock the resources and optionally return an object (file, lock, etc.).**
+* **Exit() should release the resources (for example close a file, release a lock, etc.).**
 * **Any exception that happens inside the with block is passed to the exit() method.**
 * **The exit() method can suppress the exception by returning a true value.**
 ```python
@@ -1257,7 +1247,7 @@ True
 
 ### Collection
 * **Only required methods are iter() and len(). Len() should return the number of items.**
-* **This cheatsheet actually means `'<iterable>'` when it uses `'<collection>'`.**
+* **This cheatsheet actually means `'<iterable>'` when it uses the `'<collection>'`.**
 * **I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'. The main drawback of this decision is that the reader could think a certain function doesn't accept iterators when it does, since iterators are the only built-in objects that are iterable but are not collections.**
 ```python
 class MyCollection:
@@ -1272,8 +1262,7 @@ class MyCollection:
 ```
 
 ### Sequence
-* **Only required methods are getitem() and len().**
-* **Getitem() should return an item at the passed index or raise IndexError.**
+* **Only required methods are getitem() and len(). Getitem() should return the item at the passed index or raise IndexError (it may also support negative indices and/or slices).**
 * **Iter() and contains() automatically work on any object that has getitem() defined.**
 * **Reversed() automatically works on any object that has getitem() and len() defined. It returns reversed iterator of object's items.**
 ```python
@@ -1293,12 +1282,12 @@ class MySequence:
 ```
 
 #### Discrepancies between glossary definitions and abstract base classes:
-* **Glossary on Python's website defines iterable as any object with iter() or getitem() and sequence as any object with getitem() and len(). It does not define collection.**
-* **Passing ABC Iterable to isinstance() or issubclass() checks whether object/class has method iter(), while ABC Collection checks for iter(), contains() and len().**
+* **Python's glossary defines iterable as any object with special methods iter() and/or getitem() and sequence as any object with getitem() and len(). It doesn't define collection.**
+* **Passing ABC Iterable to isinstance() or issubclass() only checks whether object/class has special method iter(), while ABC Collection checks for iter(), contains() and len().**
 
 ### ABC Sequence
-* **It's a richer interface than the basic sequence.**
-* **Extending it generates iter(), contains(), reversed(), index() and count().**
+* **It's a richer interface than the basic sequence that also requires just getitem() and len().**
+* **Extending it generates iter(), contains(), reversed(), index() and count() special methods.**
 * **Unlike `'abc.Iterable'` and `'abc.Collection'`, it is not a duck type. That is why `'issubclass(MySequence, abc.Sequence)'` would return False even if MySequence had all the methods defined. It however recognizes list, tuple, range, str, bytes, bytearray, array, memoryview and deque, since they are registered as Sequence's virtual subclasses.**
 ```python
 from collections import abc
@@ -1341,8 +1330,8 @@ from enum import Enum, auto
 ```python
 class <enum_name>(Enum):
     <member_name> = auto()              # Increment of the last numeric value or 1.
-    <member_name> = <value>             # Values don't have to be hashable.
-    <member_name> = <el_1>, <el_2>      # Values can be collections (this is a tuple).
+    <member_name> = <value>             # Values don't have to be hashable or unique.
+    <member_name> = <el_1>, <el_2>      # Values can be collections. This is a tuple.
 ```
 * **Methods receive the member they were called on as the 'self' argument.**
 * **Accessing a member named after a reserved keyword causes SyntaxError.**
@@ -1351,20 +1340,20 @@ class <enum_name>(Enum):
 <member> = <enum>.<member_name>         # Returns a member. Raises AttributeError.
 <member> = <enum>['<member_name>']      # Returns a member. Raises KeyError.
 <member> = <enum>(<value>)              # Returns a member. Raises ValueError.
-<str>    = <member>.name                # Returns member's name.
-<obj>    = <member>.value               # Returns member's value.
+<str>    = <member>.name                # Returns the member's name.
+<obj>    = <member>.value               # Returns the member's value.
 ```
 
 ```python
-<list>   = list(<enum>)                 # Returns enum's members.
-<list>   = [a.name for a in <enum>]     # Returns enum's member names.
-<list>   = [a.value for a in <enum>]    # Returns enum's member values.
+<list>   = list(<enum>)                 # Returns a list of enum's members.
+<list>   = <enum>._member_names_        # Returns a list of member names.
+<list>   = [m.value for m in <enum>]    # Returns a list of member values.
 ```
 
 ```python
-<enum>   = type(<member>)               # Returns member's enum.
-<iter>   = itertools.cycle(<enum>)      # Returns endless iterator of members.
-<member> = random.choice(list(<enum>))  # Returns a random member.
+<enum>   = type(<member>)               # Returns an enum. Also <memb>.__class__.
+<iter>   = itertools.cycle(<enum>)      # Returns an endless iterator of members.
+<member> = random.choice(list(<enum>))  # Randomly selects one of the members.
 ```
 
 ### Inline
@@ -1406,8 +1395,8 @@ finally:
 ```
 * **Code inside the `'else'` block will only be executed if `'try'` block had no exceptions.**
 * **Code inside the `'finally'` block will always be executed (unless a signal is received).**
-* **All variables that are initialized in executed blocks are also visible in all subsequent blocks, as well as outside the try statement (only function block delimits scope).**
-* **To catch signals use `'signal.signal(signal_number, <func>)'`.**
+* **All variables that are initialized in executed blocks are also visible in all subsequent blocks, as well as outside the try statement (only the function block delimits scope).**
+* **To catch signals use `'signal.signal(signal_number, handler_function)'`.**
 
 ### Catching Exceptions
 ```python
@@ -1416,10 +1405,10 @@ except <exception> as <name>: ...
 except (<exception>, [...]): ...
 except (<exception>, [...]) as <name>: ...
 ```
-* **Also catches subclasses of the exception.**
-* **Use `'traceback.print_exc()'` to print the full error message to stderr.**
-* **Use `'print(<name>)'` to print just the cause of the exception (its arguments).**
-* **Use `'logging.exception(<str>)'` to log the passed message, followed by the full error message of the caught exception. For details see [logging](#logging).**
+* **Also catches subclasses, e.g. `'IndexError'` is caught by `'except LookupError:'`.**
+* **Use `'traceback.print_exc()'` to print the full error message to standard error stream.**
+* **Use `'print(<name>)'` to print just the cause of the exception (that is, its arguments).**
+* **Use `'logging.exception(<str>)'` to log the passed message, followed by the full error message of the caught exception. For details about setting up the logger see [Logging](#logging).**
 * **Use `'sys.exc_info()'` to get exception type, object, and traceback of caught exception.**
 
 ### Raising Exceptions
@@ -1442,7 +1431,7 @@ arguments = <name>.args
 exc_type  = <name>.__class__
 filename  = <name>.__traceback__.tb_frame.f_code.co_filename
 func_name = <name>.__traceback__.tb_frame.f_code.co_name
-line      = linecache.getline(filename, <name>.__traceback__.tb_lineno)
+line_str  = linecache.getline(filename, <name>.__traceback__.tb_lineno)
 trace_str = ''.join(traceback.format_tb(<name>.__traceback__))
 error_msg = ''.join(traceback.format_exception(type(<name>), <name>, <name>.__traceback__))
 ```
@@ -1450,25 +1439,25 @@ error_msg = ''.join(traceback.format_exception(type(<name>), <name>, <name>.__tr
 ### Built-in Exceptions
 ```text
 BaseException
- +-- SystemExit                   # Raised by the sys.exit() function.
- +-- KeyboardInterrupt            # Raised when the user hits the interrupt key (ctrl-c).
+ +-- SystemExit                   # Raised by the sys.exit() function (see #Exit for details).
+ +-- KeyboardInterrupt            # Raised when the user hits the interrupt key (control-c).
  +-- Exception                    # User-defined exceptions should be derived from this class.
       +-- ArithmeticError         # Base class for arithmetic errors such as ZeroDivisionError.
       +-- AssertionError          # Raised by `assert <exp>` if expression returns false value.
       +-- AttributeError          # Raised when object doesn't have requested attribute/method.
       +-- EOFError                # Raised by input() when it hits an end-of-file condition.
       +-- LookupError             # Base class for errors when a collection can't find an item.
-      |    +-- IndexError         # Raised when a sequence index is out of range.
+      |    +-- IndexError         # Raised when index of a sequence (list/str) is out of range.
       |    +-- KeyError           # Raised when a dictionary key or set element is missing.
       +-- MemoryError             # Out of memory. May be too late to start deleting variables.
       +-- NameError               # Raised when nonexistent name (variable/func/class) is used.
       |    +-- UnboundLocalError  # Raised when local name is used before it's being defined.
-      +-- OSError                 # Errors such as FileExistsError/TimeoutError (see #Open).
-      |    +-- ConnectionError    # Errors such as BrokenPipeError/ConnectionAbortedError.
+      +-- OSError                 # Errors such as FileExistsError, TimeoutError (see #Open).
+      |    +-- ConnectionError    # Errors such as BrokenPipeError and ConnectionAbortedError.
       +-- RuntimeError            # Raised by errors that don't fall into other categories.
       |    +-- NotImplementedEr…  # Can be raised by abstract methods or by unfinished code.
-      |    +-- RecursionError     # Raised when the maximum recursion depth is exceeded.
-      +-- StopIteration           # Raised when an empty iterator is passed to next().
+      |    +-- RecursionError     # Raised if max recursion depth is exceeded (3k by default).
+      +-- StopIteration           # Raised when exhausted (empty) iterator is passed to next().
       +-- TypeError               # When an argument of the wrong type is passed to function.
       +-- ValueError              # When argument has the right type but inappropriate value.
 ```
@@ -1515,7 +1504,7 @@ Print
 ```python
 print(<el_1>, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
 ```
-* **Use `'file=sys.stderr'` for messages about errors.**
+* **Use `'file=sys.stderr'` for messages about errors so they can be processed separately.**
 * **Stdout and stderr streams hold output in a buffer until they receive a string containing '\n' or '\r', buffer reaches 4096 characters, `'flush=True'` is used, or program exits.**
 
 ### Pretty Print
@@ -1530,11 +1519,11 @@ pprint(<collection>, width=80, depth=None, compact=False, sort_dicts=True)
 Input
 -----
 ```python
-<str> = input(prompt=None)
+<str> = input()
 ```
 * **Reads a line from the user input or pipe if present (trailing newline gets stripped).**
-* **Prompt string is printed to the standard output before input is read.**
-* **Raises EOFError when user hits EOF (ctrl-d/ctrl-z⏎) or input stream gets exhausted.**
+* **If argument is passed, it gets printed to the standard output before input is read.**
+* **EOFError is raised if user hits EOF (ctrl-d/ctrl-z⏎) or if stream is already exhausted.**
 
 
 Command Line Arguments
@@ -1548,7 +1537,7 @@ arguments    = sys.argv[1:]
 ### Argument Parser
 ```python
 from argparse import ArgumentParser, FileType
-p = ArgumentParser(description=<str>)                             # Returns a parser.
+p = ArgumentParser(description=<str>)                             # Returns a parser object.
 p.add_argument('-<short_name>', '--<name>', action='store_true')  # Flag (defaults to False).
 p.add_argument('-<short_name>', '--<name>', type=<type>)          # Option (defaults to None).
 p.add_argument('<name>', type=<type>, nargs=1)                    # Mandatory first argument.
@@ -1559,18 +1548,18 @@ args  = p.parse_args()                                            # Exits on par
 ```
 
 * **Use `'help=<str>'` to set argument description that will be displayed in help message.**
-* **Use `'default=<obj>'` to set option's or optional argument's default value.**
-* **Use `'type=FileType(<mode>)'` for files. Accepts 'encoding', but 'newline' is None.**
+* **Use `'default=<obj>'` to override None as option's or optional argument's default value.**
+* **Use `'type=FileType(<mode>)'` for files. It accepts 'encoding', but 'newline' is None.**
 
 
 Open
 ----
-**Opens the file and returns a corresponding file object.**
+**Opens a file and returns the corresponding file object.**
 
 ```python
 <file> = open(<path>, mode='r', encoding=None, newline=None)
 ```
-* **`'encoding=None'` means that the default encoding is used, which is platform dependent. Best practice is to use `'encoding="utf-8"'` whenever possible.**
+* **`'encoding=None'` means that the default encoding is used, which is platform dependent. Best practice is to use `'encoding="utf-8"'` until it becomes the default (Python 3.15).**
 * **`'newline=None'` means all different end of line combinations are converted to '\n' on read, while on write all '\n' characters are converted to system's default line separator.**
 * **`'newline=""'` means no conversions take place, but input is still broken into chunks by readline() and readlines() on every '\n', '\r' and '\r\n'.**
 
@@ -1582,7 +1571,7 @@ Open
 * **`'w+'` - Read and write. Deletes existing contents.**
 * **`'r+'` - Read and write from the start.**
 * **`'a+'` - Read and write from the end.**
-* **`'b'`  - Binary mode (`'rb'`, `'wb'`, `'xb'`, …)**
+* **`'b'`  - Binary mode (`'rb'`, `'wb'`, `'xb'`, …).**
 
 ### Exceptions
 * **`'FileNotFoundError'` can be raised when reading with `'r'` or `'r+'`.**
@@ -1592,21 +1581,21 @@ Open
 
 ### File Object
 ```python
-<file>.seek(0)                      # Moves to the start of the file.
+<file>.seek(0)                      # Moves current position to the start of file.
 <file>.seek(offset)                 # Moves 'offset' chars/bytes from the start.
-<file>.seek(0, 2)                   # Moves to the end of the file.
+<file>.seek(0, 2)                   # Moves current position to the end of file.
 <bin_file>.seek(±offset, origin)    # Origin: 0 start, 1 current position, 2 end.
 ```
 
 ```python
-<str/bytes> = <file>.read(size=-1)  # Reads 'size' chars/bytes or until EOF.
+<str/bytes> = <file>.read(size=-1)  # Reads 'size' chars/bytes or until the EOF.
 <str/bytes> = <file>.readline()     # Returns a line or empty string/bytes on EOF.
-<list>      = <file>.readlines()    # Returns a list of remaining lines.
-<str/bytes> = next(<file>)          # Returns a line using buffer. Do not mix.
+<list>      = <file>.readlines()    # Returns remaining lines. Also list(<file>).
+<str/bytes> = next(<file>)          # Returns a line using a read-ahead buffer.
 ```
 
 ```python
-<file>.write(<str/bytes>)           # Writes a string or bytes object.
+<file>.write(<str/bytes>)           # Writes a str or bytes object to write buffer.
 <file>.writelines(<collection>)     # Writes a coll. of strings or bytes objects.
 <file>.flush()                      # Flushes write buffer. Runs every 4096/8192 B.
 <file>.close()                      # Closes the file after flushing write buffer.
@@ -1637,7 +1626,7 @@ from pathlib import Path
 
 ```python
 <str>  = os.getcwd()                # Returns working dir. Starts as shell's $PWD.
-<str>  = os.path.join(<path>, ...)  # Joins two or more pathname components.
+<str>  = os.path.join(<path>, ...)  # Uses os.sep to join strings or Path objects.
 <str>  = os.path.realpath(<path>)   # Resolves symlinks and calls path.abspath().
 ```
 
@@ -1648,19 +1637,19 @@ from pathlib import Path
 ```
 
 ```python
-<list> = os.listdir(path='.')       # Returns filenames located at the path.
+<list> = os.listdir(path='.')       # Returns all filenames located at the path.
 <list> = glob.glob('<pattern>')     # Returns paths matching the wildcard pattern.
 ```
 
 ```python
-<bool> = os.path.exists(<path>)     # Or: <Path>.exists()
-<bool> = os.path.isfile(<path>)     # Or: <DirEntry/Path>.is_file()
-<bool> = os.path.isdir(<path>)      # Or: <DirEntry/Path>.is_dir()
+<bool> = os.path.exists(<path>)     # Checks if path exists. Also <Path>.exists().
+<bool> = os.path.isfile(<path>)     # Also <Path>.is_file() and <DirEntry>.is_file().
+<bool> = os.path.isdir(<path>)      # Also <Path>.is_dir() and <DirEntry>.is_dir().
 ```
 
 ```python
-<stat> = os.stat(<path>)            # Or: <DirEntry/Path>.stat()
-<num>  = <stat>.st_mtime/st_size/…  # Modification time, size in bytes, ...
+<stat> = os.stat(<path>)            # File's status. Also <Path/DirEntry>.stat().
+<num>  = <stat>.st_mtime/st_size/…  # Returns modification time, size in bytes, etc.
 ```
 
 ### DirEntry
@@ -1668,9 +1657,9 @@ from pathlib import Path
 
 ```python
 <iter> = os.scandir(path='.')       # Returns DirEntry objects located at the path.
-<str>  = <DirEntry>.path            # Returns the whole path as a string.
-<str>  = <DirEntry>.name            # Returns final component as a string.
-<file> = open(<DirEntry>)           # Opens the file and returns a file object.
+<str>  = <DirEntry>.path            # Is absolute if 'path' argument was absolute.
+<str>  = <DirEntry>.name            # Returns path's final component as a string.
+<file> = open(<DirEntry>)           # Opens the file and returns its file object.
 ```
 
 ### Path Object
@@ -1681,18 +1670,18 @@ from pathlib import Path
 ```
 
 ```python
-<Path> = Path()                     # Returns relative CWD. Also Path('.').
+<Path> = Path()                     # Returns current working dir. Also Path('.').
 <Path> = Path.cwd()                 # Returns absolute CWD. Also Path().resolve().
 <Path> = Path.home()                # Returns user's home directory (absolute).
-<Path> = Path(__file__).resolve()   # Returns script's path if CWD wasn't changed.
+<Path> = Path(__file__).resolve()   # Returns module's path if CWD wasn't changed.
 ```
 
 ```python
 <Path> = <Path>.parent              # Returns Path without the final component.
-<str>  = <Path>.name                # Returns final component as a string.
-<str>  = <Path>.stem                # Returns final component without extension.
-<str>  = <Path>.suffix              # Returns final component's extension.
-<tup.> = <Path>.parts               # Returns all components as strings.
+<str>  = <Path>.name                # Returns path's final component as a string.
+<str>  = <Path>.suffix              # Returns name's last extension, e.g. '.gz'.
+<str>  = <Path>.stem                # Returns name without the last extension.
+<tup.> = <Path>.parts               # Returns all path's components as strings.
 ```
 
 ```python
@@ -1701,8 +1690,8 @@ from pathlib import Path
 ```
 
 ```python
-<str>  = str(<Path>)                # Returns path as a string.
-<file> = open(<Path>)               # Also <Path>.read/write_text/bytes(<args>).
+<str>  = str(<Path>)                # Returns path as string. Also <Path>.as_uri().
+<file> = open(<Path>)               # Also <Path>.read_text/write_bytes(<args>).
 ```
 
 
@@ -1713,7 +1702,7 @@ import os, shutil, subprocess
 ```
 
 ```python
-os.chdir(<path>)                    # Changes the current working directory.
+os.chdir(<path>)                    # Changes the current working directory (CWD).
 os.mkdir(<path>, mode=0o777)        # Creates a directory. Permissions are in octal.
 os.makedirs(<path>, mode=0o777)     # Creates all path's dirs. Also `exist_ok=False`.
 ```
@@ -1725,18 +1714,18 @@ shutil.copytree(from, to)           # Copies the directory. 'to' must not exist.
 ```
 
 ```python
-os.rename(from, to)                 # Renames/moves the file or directory.
+os.rename(from, to)                 # Renames or moves the file or directory 'from'.
 os.replace(from, to)                # Same, but overwrites file 'to' even on Windows.
 shutil.move(from, to)               # Rename() that moves into 'to' if it's a dir.
 ```
 
 ```python
-os.remove(<path>)                   # Deletes the file.
-os.rmdir(<path>)                    # Deletes the empty directory.
-shutil.rmtree(<path>)               # Deletes the directory.
+os.remove(<path>)                   # Deletes the file. Or `pip3 install send2trash`.
+os.rmdir(<path>)                    # Deletes the empty directory or raises OSError.
+shutil.rmtree(<path>)               # Deletes the directory and all of its contents.
 ```
-* **Paths can be either strings, Paths, or DirEntry objects.**
-* **Functions report OS related errors by raising either OSError or one of its [subclasses](#exceptions-1).**
+* **Paths can be either strings, Path objects, or DirEntry objects.**
+* **Functions report OS related errors by raising OSError or one of its [subclasses](#exceptions-1).**
 
 ### Shell Commands
 ```python
@@ -1745,7 +1734,7 @@ shutil.rmtree(<path>)               # Deletes the directory.
 <int>  = <pipe>.close()             # Returns None if last command exited with returncode 0.
 ```
 
-#### Sends '1 + 1' to the basic calculator and captures its output:
+#### Sends "1 + 1" to the basic calculator and captures its output:
 ```python
 >>> subprocess.run('bc', input='1 + 1\n', capture_output=True, text=True)
 CompletedProcess(args='bc', returncode=0, stdout='2\n', stderr='')
@@ -1768,22 +1757,22 @@ JSON
 
 ```python
 import json
-<str>    = json.dumps(<object>)     # Converts object to JSON string.
-<object> = json.loads(<str>)        # Converts JSON string to object.
+<str>  = json.dumps(<list/dict>)    # Converts collection to JSON string.
+<coll> = json.loads(<str>)          # Converts JSON string to collection.
 ```
 
-### Read Object from JSON File
+### Read Collection from JSON File
 ```python
 def read_json_file(filename):
     with open(filename, encoding='utf-8') as file:
         return json.load(file)
 ```
 
-### Write Object to JSON File
+### Write Collection to JSON File
 ```python
-def write_to_json_file(filename, an_object):
+def write_to_json_file(filename, collection):
     with open(filename, 'w', encoding='utf-8') as file:
-        json.dump(an_object, file, ensure_ascii=False, indent=2)
+        json.dump(collection, file, ensure_ascii=False, indent=2)
 ```
 
 
@@ -1797,14 +1786,14 @@ import pickle
 <object> = pickle.loads(<bytes>)    # Converts bytes object to object.
 ```
 
-### Read Object from File
+### Read Object from Pickle File
 ```python
 def read_pickle_file(filename):
     with open(filename, 'rb') as file:
         return pickle.load(file)
 ```
 
-### Write Object to File
+### Write Object to Pickle File
 ```python
 def write_to_pickle_file(filename, an_object):
     with open(filename, 'wb') as file:
@@ -1820,33 +1809,34 @@ CSV
 import csv
 ```
 
-### Read
 ```python
-<reader> = csv.reader(<file>)       # Also: `dialect='excel', delimiter=','`.
-<list>   = next(<reader>)           # Returns next row as a list of strings.
-<list>   = list(<reader>)           # Returns a list of remaining rows.
+<file>   = open(<path>, newline='')       # Opens the CSV (text) file for reading.
+<reader> = csv.reader(<file>)             # Also: `dialect='excel', delimiter=','`.
+<list>   = next(<reader>)                 # Returns next row as a list of strings.
+<list>   = list(<reader>)                 # Returns a list of all remaining rows.
 ```
-* **File must be opened with a `'newline=""'` argument, or newlines embedded inside quoted fields will not be interpreted correctly!**
-* **To print the spreadsheet to the console use [Tabulate](#table) library.**
-* **For XML and binary Excel files (xlsx, xlsm and xlsb) use [Pandas](#dataframe-plot-encode-decode) library.**
-* **Reader accepts any iterator of strings, not just files.**
+* **Without the `'newline=""'` argument, every '\r\n' sequence that is embedded inside a quoted field will get converted to '\n'! For details about newline argument see [Open](#open).**
+* **To print the spreadsheet to the console use [Tabulate](#table) or PrettyTable library.**
+* **For XML and binary Excel files (xlsx, xlsm and xlsb) use [Pandas](#fileformats) library.**
+* **Reader accepts any iterator (or collection) of strings, not just files.**
 
 ### Write
 ```python
-<writer> = csv.writer(<file>)       # Also: `dialect='excel', delimiter=','`.
-<writer>.writerow(<collection>)     # Encodes objects using `str(<el>)`.
-<writer>.writerows(<coll_of_coll>)  # Appends multiple rows.
+<file>   = open(<path>, 'w', newline='')  # Opens the CSV (text) file for writing.
+<writer> = csv.writer(<file>)             # Also: `dialect='excel', delimiter=','`.
+<writer>.writerow(<collection>)           # Encodes each object using `str(<el>)`.
+<writer>.writerows(<coll_of_coll>)        # Appends multiple rows to the file.
 ```
-* **File must be opened with a `'newline=""'` argument, or '\r' will be added in front of every '\n' on platforms that use '\r\n' line endings!**
+* **If file is opened without the `'newline=""'` argument, '\r' will be added in front of every '\n' on platforms that use '\r\n' line endings (i.e., newlines may get doubled on Windows)!**
 * **Open existing file with `'mode="a"'` to append to it or `'mode="w"'` to overwrite it.**
 
 ### Parameters
 * **`'dialect'` - Master parameter that sets the default values. String or a 'csv.Dialect' object.**
-* **`'delimiter'` - A one-character string used to separate fields.**
-* **`'lineterminator'` - How writer terminates rows. Reader is hardcoded to '\n', '\r', '\r\n'.**
-* **`'quotechar'` - Character for quoting fields that contain special characters.**
-* **`'escapechar'` - Character for escaping quotechars.**
-* **`'doublequote'` - Whether quotechars inside fields are/get doubled or escaped.**
+* **`'delimiter'` - A one-character string that separates fields (comma, tab, semicolon, etc.).**
+* **`'lineterminator'` - How writer terminates rows. Reader looks for '\n', '\r' and '\r\n'.**
+* **`'quotechar'` - Character for quoting fields containing delimiters, quotechars, '\n' or '\r'.**
+* **`'escapechar'` - Character for escaping quotechars (not needed if doublequote is True).**
+* **`'doublequote'` - Whether quotechars inside fields are/get doubled instead of escaped.**
 * **`'quoting'` - 0: As necessary, 1: All, 2: All but numbers which are read as floats, 3: None.**
 * **`'skipinitialspace'` - Is space character at the start of the field stripped by the reader.**
 
@@ -1883,50 +1873,50 @@ def write_to_csv_file(filename, rows, mode='w', **csv_params):
 
 SQLite
 ------
-**A server-less database engine that stores each database into a separate file.**
+**A server-less database engine that stores each database into its own file.**
 
 ```python
 import sqlite3
-<conn> = sqlite3.connect(<path>)                # Opens existing or new file. Also ':memory:'.
-<conn>.close()                                  # Closes connection. Discards uncommitted data.
+<conn> = sqlite3.connect(<path>)               # Opens existing or new file. Also ':memory:'.
+<conn>.close()                                 # Closes connection. Discards uncommitted data.
 ```
 
 ### Read
 ```python
-<cursor> = <conn>.execute('<query>')            # Can raise a subclass of sqlite3.Error.
-<tuple>  = <cursor>.fetchone()                  # Returns next row. Also next(<cursor>).
-<list>   = <cursor>.fetchall()                  # Returns remaining rows. Also list(<cursor>).
+<cursor> = <conn>.execute('<query>')           # Can raise a subclass of sqlite3.Error.
+<tuple>  = <cursor>.fetchone()                 # Returns the next row. Also next(<cursor>).
+<list>   = <cursor>.fetchall()                 # Returns remaining rows. Also list(<cursor>).
 ```
 
 ### Write
 ```python
-<conn>.execute('<query>')                       # Can raise a subclass of sqlite3.Error.
-<conn>.commit()                                 # Saves all changes since the last commit.
-<conn>.rollback()                               # Discards all changes since the last commit.
+<conn>.execute('<query>')                      # Can raise a subclass of sqlite3.Error.
+<conn>.commit()                                # Saves all changes since the last commit.
+<conn>.rollback()                              # Discards all changes since the last commit.
 ```
 
 #### Or:
 ```python
-with <conn>:                                    # Exits the block with commit() or rollback(),
-    <conn>.execute('<query>')                   # depending on whether any exception occurred.
+with <conn>:                                   # Exits the block with commit() or rollback(),
+    <conn>.execute('<query>')                  # depending on whether any exception occurred.
 ```
 
 ### Placeholders
 ```python
-<conn>.execute('<query>', <list/tuple>)         # Replaces '?'s in query with values.
-<conn>.execute('<query>', <dict/namedtuple>)    # Replaces ':<key>'s with values.
-<conn>.executemany('<query>', <coll_of_above>)  # Runs execute() multiple times.
+<conn>.execute('<query>', <list/tuple>)        # Replaces every question mark with an item.
+<conn>.execute('<query>', <dict/namedtuple>)   # Replaces every :<key> with a matching value.
+<conn>.executemany('<query>', <coll_of_coll>)  # Runs execute() once for each collection.
 ```
-* **Passed values can be of type str, int, float, bytes, None or bool (stored as 1 or 0).**
+* **Passed values can be of type str, int, float, bytes, None, or bool (stored as 1 or 0).**
+* **SQLite does not restrict columns to any type unless table is declared as strict.**
 
 ### Example
 **Values are not actually saved in this example because `'conn.commit()'` is omitted!**
 ```python
 >>> conn = sqlite3.connect('test.db')
->>> conn.execute('CREATE TABLE person (person_id INTEGER PRIMARY KEY, name, height)')
->>> conn.execute('INSERT INTO person VALUES (NULL, ?, ?)', ('Jean-Luc', 187)).lastrowid
-1
->>> conn.execute('SELECT * FROM person').fetchall()
+>>> conn.execute('CREATE TABLE person (name TEXT, height INTEGER) STRICT')
+>>> conn.execute('INSERT INTO person VALUES (?, ?)', ('Jean-Luc', 187))
+>>> conn.execute('SELECT rowid, * FROM person').fetchall()
 [(1, 'Jean-Luc', 187)]
 ```
 
@@ -1935,10 +1925,10 @@ with <conn>:                                    # Exits the block with commit()
 ```python
 # $ pip3 install sqlalchemy
 from sqlalchemy import create_engine, text
-<engine> = create_engine('<url>')               # Url: 'dialect://user:password@host/dbname'.
-<conn>   = <engine>.connect()                   # Creates a connection. Also <conn>.close().
-<cursor> = <conn>.execute(text('<query>'), …)   # Replaces ':<key>'s with keyword arguments.
-with <conn>.begin(): ...                        # Exits the block with commit or rollback.
+<engine> = create_engine('<url>')              # Url: 'dialect://user:password@host/dbname'.
+<conn>   = <engine>.connect()                  # Creates a connection. Also <conn>.close().
+<cursor> = <conn>.execute(text('<query>'), …)  # `<dict>`. Replaces every :<key> with value.
+with <conn>.begin(): ...                       # Exits the block with commit or rollback.
 ```
 
 ```text
@@ -1959,14 +1949,14 @@ Bytes
 
 ```python
 <bytes> = b'<str>'                       # Only accepts ASCII characters and \x00-\xff.
-<int>   = <bytes>[index]                 # Returns an int in range from 0 to 255.
+<int>   = <bytes>[index]                 # Returns an integer in range from 0 to 255.
 <bytes> = <bytes>[<slice>]               # Returns bytes even if it has only one element.
-<bytes> = <bytes>.join(<coll_of_bytes>)  # Joins elements using bytes as a separator.
+<bytes> = <bytes>.join(<coll_of_bytes>)  # Joins elements by using bytes as a separator.
 ```
 
 ### Encode
 ```python
-<bytes> = bytes(<coll_of_ints>)          # Ints must be in range from 0 to 255.
+<bytes> = bytes(<coll_of_ints>)          # Integers must be in range from 0 to 255.
 <bytes> = bytes(<str>, 'utf-8')          # Encodes the string. Also <str>.encode().
 <bytes> = bytes.fromhex('<hex>')         # Hex pairs can be separated by whitespaces.
 <bytes> = <int>.to_bytes(n_bytes, …)     # `byteorder='big/little', signed=False`.
@@ -1974,7 +1964,7 @@ Bytes
 
 ### Decode
 ```python
-<list>  = list(<bytes>)                  # Returns ints in range from 0 to 255.
+<list>  = list(<bytes>)                  # Returns integers in range from 0 to 255.
 <str>   = str(<bytes>, 'utf-8')          # Returns a string. Also <bytes>.decode().
 <str>   = <bytes>.hex()                  # Returns hex pairs. Accepts `sep=<str>`.
 <int>   = int.from_bytes(<bytes>, …)     # `byteorder='big/little', signed=False`.
@@ -2003,7 +1993,7 @@ Struct
 ```python
 from struct import pack, unpack
 
-<bytes> = pack('<format>', <el_1> [, ...])  # Packs objects according to format string.
+<bytes> = pack('<format>', <el_1> [, ...])  # Packs numbers according to format string.
 <tuple> = unpack('<format>', <bytes>)       # Use iter_unpack() to get iterator of tuples.
 ```
 
@@ -2038,22 +2028,22 @@ b'\x00\x01\x00\x02\x00\x00\x00\x03'
 
 Array
 -----
-**List that can only hold numbers of a predefined type. Available types and their minimum sizes in bytes are listed above. Type sizes and byte order are always determined by the system, however bytes of each element can be reversed with byteswap() method.**
+**List that can only hold numbers of a predefined type. Available types and their minimum sizes in bytes are listed above. Type sizes and byte order are always determined by the system, however bytes of each element can be reversed (by calling the byteswap() method).**
 
 ```python
 from array import array
 ```
 
 ```python
-<array> = array('<typecode>', <coll_of_nums>)  # Array from collection of numbers.
-<array> = array('<typecode>', <bytes>)         # Copies bytes to array's memory.
-<array> = array('<typecode>', <array>)         # Treats array as a sequence of numbers.
-<array>.fromfile(<file>, n_items)              # Appends items from the binary file.
+<array> = array('<typecode>', <coll_of_nums>)  # Creates an array from collection of numbers.
+<array> = array('<typecode>', <bytes>)         # Writes passed bytes to the array's memory.
+<array> = array('<typecode>', <array>)         # Treats passed array as a sequence of numbers.
+<array>.fromfile(<file>, n_items)              # Appends file contents to the array's memory.
 ```
 
 ```python
-<bytes> = bytes(<array>)                       # Returns a copy of array's memory.
-<file>.write(<array>)                          # Writes array's memory to binary file.
+<bytes> = bytes(<array>)                       # Returns a copy of array's memory as bytes.
+<file>.write(<array>)                          # Writes array's memory to the binary file.
 ```
 
 
@@ -2063,7 +2053,7 @@ Memory View
 
 ```python
 <mview> = memoryview(<bytes/bytearray/array>)  # Immutable if bytes is passed, else mutable.
-<obj>   = <mview>[index]                       # Returns int or float. Bytes if format is 'c'.
+<obj>   = <mview>[index]                       # Returns ints/floats. Bytes if format is 'c'.
 <mview> = <mview>[<slice>]                     # Returns memoryview with rearranged elements.
 <mview> = <mview>.cast('<typecode>')           # Only works between B/b/c and other types.
 <mview>.release()                              # Releases memory buffer of the base object.
@@ -2078,14 +2068,14 @@ Memory View
 
 ```python
 <list>  = list(<mview>)                        # Returns a list of ints, floats or bytes.
-<str>   = str(<mview>, 'utf-8')                # Treats memoryview as a bytes object.
+<str>   = str(<mview>, 'utf-8')                # Treats passed memoryview as a bytes object.
 <str>   = <mview>.hex()                        # Returns hex pairs. Accepts `sep=<str>`.
 ```
 
 
 Deque
 -----
-**A thread-safe list with efficient appends and pops from either side. Pronounced "deck".**
+**List with efficient appends and pops from either side.**
 
 ```python
 from collections import deque
@@ -2094,80 +2084,15 @@ from collections import deque
 ```python
 <deque> = deque(<collection>)                  # Use `maxlen=<int>` to set size limit.
 <deque>.appendleft(<el>)                       # Opposite element is dropped if full.
-<deque>.extendleft(<collection>)               # Passed collection gets reversed.
-<deque>.rotate(n=1)                            # Last element becomes first.
+<deque>.extendleft(<collection>)               # Prepends reversed coll. to the deque.
+<deque>.rotate(n=1)                            # Last element becomes the first one.
 <el> = <deque>.popleft()                       # Raises IndexError if deque is empty.
 ```
 
 
-Threading
----------
-**CPython interpreter can only run a single thread at a time. Using multiple threads won't result in a faster execution, unless at least one of the threads contains an I/O operation.**
-```python
-from threading import Thread, Lock, RLock, Semaphore, Event, Barrier
-from concurrent.futures import ThreadPoolExecutor, as_completed
-```
-
-### Thread
-```python
-<Thread> = Thread(target=<function>)           # Use `args=<collection>` to set the arguments.
-<Thread>.start()                               # Starts the thread. Also <Thread>.is_alive().
-<Thread>.join()                                # Waits for the thread to finish.
-```
-* **Use `'kwargs=<dict>'` to pass keyword arguments to the function.**
-* **Use `'daemon=True'`, or the program will not be able to exit while the thread is alive.**
-
-### Lock
-```python
-<lock> = Lock/RLock()                          # RLock can only be released by acquirer.
-<lock>.acquire()                               # Waits for the lock to be available.
-<lock>.release()                               # Makes the lock available again.
-```
-
-#### Or:
-```python
-with <lock>:                                   # Enters the block by calling acquire() and
-    ...                                        # exits it with release(), even on error.
-```
-
-### Semaphore, Event, Barrier
-```python
-<Semaphore> = Semaphore(value=1)               # Lock that can be acquired by 'value' threads.
-<Event>     = Event()                          # Method wait() blocks until set() is called.
-<Barrier>   = Barrier(n_times)                 # Wait() blocks until it's called n_times.
-```
-
-### Queue
-```python
-<Queue> = queue.Queue(maxsize=0)               # A thread-safe first-in-first-out queue.
-<Queue>.put(<el>)                              # Blocks until queue stops being full.
-<Queue>.put_nowait(<el>)                       # Raises queue.Full exception if full.
-<el> = <Queue>.get()                           # Blocks until queue stops being empty.
-<el> = <Queue>.get_nowait()                    # Raises queue.Empty exception if empty.
-```
-
-### Thread Pool Executor
-```python
-<Exec> = ThreadPoolExecutor(max_workers=None)  # Or: `with ThreadPoolExecutor() as <name>: ...`
-<iter> = <Exec>.map(<func>, <args_1>, ...)     # Multithreaded and non-lazy map(). Keeps order.
-<Futr> = <Exec>.submit(<func>, <arg_1>, ...)   # Creates a thread and returns its Future obj.
-<Exec>.shutdown()                              # Blocks until all threads finish executing.
-```
-
-```python
-<bool> = <Future>.done()                       # Checks if the thread has finished executing.
-<obj>  = <Future>.result(timeout=None)         # Waits for thread to finish and returns result.
-<bool> = <Future>.cancel()                     # Cancels or returns False if running/finished.
-<iter> = as_completed(<coll_of_Futures>)       # `next(<iter>)` returns next completed Future.
-```
-* **Map() and as\_completed() also accept 'timeout'. It causes futures.TimeoutError when next() is called/blocking. Map() times from original call and as_completed() from first call to next(). As\_completed() fails if next() is called too late, even if all threads are done.**
-* **Exceptions that happen inside threads are raised when map iterator's next() or Future's result() are called. Future's exception() method returns exception object or None.**
-* **ProcessPoolExecutor provides true parallelism but: everything sent to/from workers must be [pickable](#pickle), queues must be sent using executor's 'initargs' and 'initializer' parameters, and executor should only be reachable via `'if __name__ == "__main__": ...'`.**
-
-
 Operator
 --------
-**Module of functions that provide the functionality of operators. Functions are ordered by operator precedence, starting with least binding.**
+**Module of functions that provide the functionality of operators. Functions are grouped by operator precedence, from least to most binding. Functions and operators in first, third and fifth line are also ordered by precedence within a group.**
 ```python
 import operator as op
 ```
@@ -2175,19 +2100,18 @@ import operator as op
 ```python
 <bool> = op.not_(<obj>)                                        # or, and, not (or/and missing)
 <bool> = op.eq/ne/lt/ge/is_/is_not/contains(<obj>, <obj>)      # ==, !=, <, >=, is, is not, in
-<obj>  = op.or_/xor/and_(<int/set>, <int/set>)                 # |, ^, &
-<int>  = op.lshift/rshift(<int>, <int>)                        # <<, >>
-<obj>  = op.add/sub/mul/truediv/floordiv/mod(<obj>, <obj>)     # +, -, *, /, //, %
-<num>  = op.neg/invert(<num>)                                  # -, ~
-<num>  = op.pow(<num>, <num>)                                  # **
+<obj>  = op.or_/xor/and_(<int/set>, <int/set>)                 # |, ^, & (sorted by precedence)
+<int>  = op.lshift/rshift(<int>, <int>)                        # <<, >> (i.e. <int> << n_bits)
+<obj>  = op.add/sub/mul/truediv/floordiv/mod(<obj>, <obj>)     # +, -, *, /, //, % (two groups)
+<num>  = op.neg/invert(<num>)                                  # -, ~ (negate and bitwise not)
+<num>  = op.pow(<num>, <num>)                                  # ** (pow() accepts 3 arguments)
 <func> = op.itemgetter/attrgetter/methodcaller(<obj> [, ...])  # [index/key], .name, .name([…])
 ```
 
 ```python
 elementwise_sum  = map(op.add, list_a, list_b)
-sorted_by_second = sorted(<coll.>, key=op.itemgetter(1))
-sorted_by_both   = sorted(<coll.>, key=op.itemgetter(1, 0))
-product_of_elems = functools.reduce(op.mul, <collection>)
+sorted_by_second = sorted(<coll>, key=op.itemgetter(1))
+sorted_by_both   = sorted(<coll>, key=op.itemgetter(1, 0))
 first_element    = op.methodcaller('pop', 0)(<list>)
 ```
 * **Most operators call the object's special method that is named after them (second object is passed as an argument), while logical operators call their own code that relies on bool().**
@@ -2196,7 +2120,7 @@ first_element    = op.methodcaller('pop', 0)(<list>)
 
 Match Statement
 ---------------
-**Executes the first block with matching pattern. Added in Python 3.10.**
+**Executes the first block with matching pattern.**
 
 ```python
 match <object/expression>:
@@ -2212,17 +2136,16 @@ match <object/expression>:
 <wildcard_patt> = _                                # Matches any object. Useful in last case.
 <capture_patt>  = <name>                           # Matches any object and binds it to name.
 <as_pattern>    = <pattern> as <name>              # Binds match to name. Also <type>(<name>).
-<or_pattern>    = <pattern> | <pattern> [| ...]    # Matches any of the patterns.
-<sequence_patt> = [<pattern>, ...]                 # Matches sequence with matching items.
-<mapping_patt>  = {<value_pattern>: <patt>, ...}   # Matches dictionary with matching items.
-<class_pattern> = <type>(<attr_name>=<patt>, ...)  # Matches object with matching attributes.
+<or_pattern>    = <pattern> | <pattern> [| ...]    # Matches if any of listed patterns match.
+<sequence_patt> = [<pattern>, ...]                 # Matches a sequence. All items must match.
+<mapping_patt>  = {<value_pattern>: <patt>, ...}   # Matches a dict that has matching items.
+<class_pattern> = <type>(<attr_name>=<patt>, ...)  # Matches an object if attributes match.
 ```
-* **Sequence pattern can also be written as a tuple.**
+* **Sequence pattern can also be written as a tuple, either with or without the brackets.**
 * **Use `'*<name>'` and `'**<name>'` in sequence/mapping patterns to bind remaining items.**
 * **Sequence pattern must match all items of the collection, while mapping pattern does not.**
-* **Patterns can be surrounded with brackets to override precedence (`'|'` > `'as'` > `','`).**
-* **Built-in types allow a single positional pattern that is matched against the entire object.**
-* **All names that are bound in the matching case, as well as variables initialized in its block, are visible after the match statement.**
+* **Patterns can be surrounded with brackets to override their precedence: `'|'` > `'as'` > `','`. For example, `'[1, 2]'` is matched by the `'case 1|2, 2|3 as x if x == 2:'` block.**
+* **All names that are bound in the matching case, as well as variables initialized in its body, are visible after the match statement (only function block delimits scope).**
 
 ### Example
 ```python
@@ -2232,7 +2155,7 @@ match <object/expression>:
 ...         parts=['/', 'home', user, *_]
 ...     ) as p if p.name.lower().startswith('readme') and p.is_file():
 ...         print(f'{p.name} is a readme file that belongs to user {user}.')
-'README.md is a readme file that belongs to user gto.'
+README.md is a readme file that belongs to user gto.
 ```
 
 
@@ -2244,9 +2167,9 @@ import logging as log
 
 ```python
 log.basicConfig(filename=<path>, level='DEBUG')   # Configures the root logger (see Setup).
-log.debug/info/warning/error/critical(<str>)      # Sends message to the root logger.
-<Logger> = log.getLogger(__name__)                # Returns logger named after the module.
-<Logger>.<level>(<str>)                           # Sends message to the logger.
+log.debug/info/warning/error/critical(<str>)      # Sends passed message to the root logger.
+<Logger> = log.getLogger(__name__)                # Returns a logger named after the module.
+<Logger>.<level>(<str>)                           # Sends the message. Same levels as above.
 <Logger>.exception(<str>)                         # Error() that appends caught exception.
 ```
 
@@ -2261,11 +2184,11 @@ log.basicConfig(
 ```
 
 ```python
-<Formatter> = log.Formatter('<format>')           # Creates a Formatter.
-<Handler> = log.FileHandler(<path>, mode='a')     # Creates a Handler. Also `encoding=None`.
-<Handler>.setFormatter(<Formatter>)               # Adds Formatter to the Handler.
-<Handler>.setLevel(<int/str>)                     # Processes all messages by default.
-<Logger>.addHandler(<Handler>)                    # Adds Handler to the Logger.
+<Formatter> = log.Formatter('<format>')           # Formats messages according to format str.
+<Handler> = log.FileHandler(<path>, mode='a')     # Appends to file. Also `encoding=None`.
+<Handler>.setFormatter(<Formatter>)               # Only outputs bare messages by default.
+<Handler>.setLevel(<int/str>)                     # Prints or saves every message by default.
+<Logger>.addHandler(<Handler>)                    # Logger can have more than one handler.
 <Logger>.setLevel(<int/str>)                      # What is sent to its/ancestors' handlers.
 <Logger>.propagate = <bool>                       # Cuts off ancestors' handlers if False.
 ```
@@ -2294,28 +2217,93 @@ CRITICAL:my_module:Running out of disk space.
 Introspection
 -------------
 ```python
-<list> = dir()                      # List of of local names (including functions and classes).
+<list> = dir()                      # Local names of variables, functions, classes and modules.
 <dict> = vars()                     # Dict of local names and their objects. Also locals().
-<dict> = globals()                  # Dict of global names (for instance '__builtin__' module).
+<dict> = globals()                  # Dict of global names and their objects, e.g. __builtin__.
 ```
 
 ```python
-<list> = dir(<obj>)                 # Returns names of all object's attributes (incl. methods).
+<list> = dir(<obj>)                 # Returns names of object's attributes (including methods).
 <dict> = vars(<obj>)                # Returns dict of writable attributes. Also <obj>.__dict__.
 <bool> = hasattr(<obj>, '<name>')   # Checks if object possesses attribute with passed name.
-value  = getattr(<obj>, '<name>')   # Returns object's attribute or raises AttributeError.
-setattr(<obj>, '<name>', value)     # Sets attribute. Only works on objects with __dict__.
+value  = getattr(<obj>, '<name>')   # Returns the object's attribute or raises AttributeError.
+setattr(<obj>, '<name>', value)     # Sets attribute. Only works on objects with __dict__ attr.
 delattr(<obj>, '<name>')            # Deletes attribute from __dict__. Also `del <obj>.<name>`.
 ```
 
 ```python
-<Sig>  = inspect.signature(<func>)  # Returns function's Signature object. Can accept a class.
+<Sig>  = inspect.signature(<func>)  # Returns Signature object of the passed function or class.
 <dict> = <Sig>.parameters           # Returns dict of Parameters. Also <Sig>.return_annotation.
 <memb> = <Param>.kind               # Returns ParameterKind member (Parameter.KEYWORD_ONLY, …).
 <type> = <Param>.annotation         # Returns Parameter.empty if missing. Also <Param>.default.
 ```
 
 
+Threading
+---------
+**CPython interpreter can only run a single thread at a time. Using multiple threads won't result in a faster execution, unless at least one of the threads contains an I/O operation.**
+```python
+from threading import Thread, Lock, RLock, Semaphore, Event, Barrier
+from concurrent.futures import ThreadPoolExecutor, as_completed
+```
+
+### Thread
+```python
+<Thread> = Thread(target=<function>)           # Use `args=<collection>` to set the arguments.
+<Thread>.start()                               # Starts the thread. Also <Thread>.is_alive().
+<Thread>.join()                                # Waits for the thread to finish executing.
+```
+* **Use `'kwargs=<dict>'` to pass keyword arguments to the function.**
+* **Use `'daemon=True'`, or the program won't be able to exit while the thread is alive.**
+
+### Lock
+```python
+<lock> = Lock/RLock()                          # RLock can only be released by acquirer.
+<lock>.acquire()                               # Waits for the lock to be available.
+<lock>.release()                               # Makes the lock available again.
+```
+
+#### Or:
+```python
+with <lock>:                                   # Enters the block by calling acquire() and
+    ...                                        # exits it with release(), even on error.
+```
+
+### Semaphore, Event, Barrier
+```python
+<Semaphore> = Semaphore(value=1)               # Lock that can be acquired by 'value' threads.
+<Event>     = Event()                          # Method wait() blocks until set() is called.
+<Barrier>   = Barrier(n_times)                 # Wait() blocks until it's called n times.
+```
+
+### Queue
+```python
+<Queue> = queue.Queue(maxsize=0)               # A thread-safe first-in-first-out queue.
+<Queue>.put(<el>)                              # Blocks until queue stops being full.
+<Queue>.put_nowait(<el>)                       # Raises queue.Full exception if full.
+<el> = <Queue>.get()                           # Blocks until queue stops being empty.
+<el> = <Queue>.get_nowait()                    # Raises queue.Empty exception if empty.
+```
+
+### Thread Pool Executor
+```python
+<Exec> = ThreadPoolExecutor(max_workers=None)  # Also `with ThreadPoolExecutor() as <name>: …`.
+<iter> = <Exec>.map(<func>, <args_1>, ...)     # Multithreaded and non-lazy map(). Keeps order.
+<Futr> = <Exec>.submit(<func>, <arg_1>, ...)   # Creates a thread and returns its Future obj.
+<Exec>.shutdown()                              # Waits for all submitted threads to finish.
+```
+
+```python
+<bool> = <Future>.done()                       # Checks if the thread has finished executing.
+<obj>  = <Future>.result(timeout=None)         # Waits for thread to finish and returns result.
+<bool> = <Future>.cancel()                     # Cancels or returns False if running/finished.
+<iter> = as_completed(<coll_of_Futures>)       # `next(<iter>)` returns next completed Future.
+```
+* **Map() and as\_completed() also accept 'timeout'. It causes futures.TimeoutError when next() is called/blocking. Map() times from original call and as_completed() from first call to next(). As\_completed() fails if next() is called too late, even if all threads are done.**
+* **Exceptions that happen inside threads are raised when map iterator's next() or Future's result() are called. Future's exception() method returns an exception object or None.**
+* **ProcessPoolExecutor provides true parallelism but: everything sent to/from workers must be [pickable](#pickle), queues must be sent using executor's 'initargs' and 'initializer' parameters, and executor should only be reachable via `'if __name__ == "__main__": ...'`.**
+
+
 Coroutines
 ----------
 * **Coroutines have a lot in common with threads, but unlike threads, they only give up control when they call another coroutine and they don’t use as much memory.**
@@ -2327,30 +2315,30 @@ import asyncio as aio
 ```
 
 ```python
-<coro> = <async_function>(<args>)         # Creates a coroutine by calling async def function.
-<obj>  = await <coroutine>                # Starts the coroutine and returns its result.
-<task> = aio.create_task(<coroutine>)     # Schedules the coroutine for execution.
-<obj>  = await <task>                     # Returns coroutine's result. Also <task>.cancel().
+<coro> = <async_function>(<args>)          # Creates a coroutine by calling async def function.
+<obj>  = await <coroutine>                 # Starts the coroutine and waits for its result.
+<task> = aio.create_task(<coroutine>)      # Schedules it for execution. Always keep the task.
+<obj>  = await <task>                      # Returns coroutine's result. Also <task>.cancel().
 ```
 
 ```python
-<coro> = aio.gather(<coro/task>, ...)     # Schedules coros. Returns list of results on await.
-<coro> = aio.wait(<tasks>, …)             # `aio.ALL/FIRST_COMPLETED`. Returns (done, pending).
-<iter> = aio.as_completed(<coros/tasks>)  # Iterator of coros. All return next result on await.
+<coro> = aio.gather(<coro/task>, ...)      # Schedules coros. Returns list of results on await.
+<coro> = aio.wait(<tasks>, return_when=…)  # `'ALL/FIRST_COMPLETED'`. Returns (done, pending).
+<iter> = aio.as_completed(<coros/tasks>)   # Iter of coros that return next result on await.
 ```
 
 #### Runs a terminal game where you control an asterisk that must avoid numbers:
 ```python
 import asyncio, collections, curses, curses.textpad, enum, random
 
-P = collections.namedtuple('P', 'x y')    # Position
-D = enum.Enum('D', 'n e s w')             # Direction
-W, H = 15, 7                              # Width, Height
+P = collections.namedtuple('P', 'x y')     # Position (x and y coordinates).
+D = enum.Enum('D', 'n e s w')              # Direction (north, east, etc.).
+W, H = 15, 7                               # Width and height constants.
 
 def main(screen):
-    curses.curs_set(0)                    # Makes cursor invisible.
-    screen.nodelay(True)                  # Makes getch() non-blocking.
-    asyncio.run(main_coroutine(screen))   # Starts running asyncio code.
+    curses.curs_set(0)                     # Makes the cursor invisible.
+    screen.nodelay(True)                   # Makes getch() non-blocking.
+    asyncio.run(main_coroutine(screen))    # Starts running asyncio code.
 
 async def main_coroutine(screen):
     moves = asyncio.Queue()
@@ -2419,9 +2407,8 @@ import matplotlib.pyplot as plt
 plt.plot/bar/scatter(x_data, y_data [, label=<str>])  # Also plt.plot(y_data).
 plt.legend()                                          # Adds a legend.
 plt.title/xlabel/ylabel(<str>)                        # Adds a title or label.
-plt.savefig(<path>)                                   # Saves the figure.
-plt.show()                                            # Displays the figure.
-plt.clf()                                             # Clears the figure.
+plt.show()                                            # Also plt.savefig(<path>).
+plt.clf()                                             # Clears the plot.
 ```
 
 
@@ -2443,7 +2430,7 @@ Console App
 ```python
 # $ pip3 install windows-curses
 import curses, os
-from curses import A_REVERSE, KEY_DOWN, KEY_UP, KEY_LEFT, KEY_RIGHT, KEY_ENTER
+from curses import A_REVERSE, KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT
 
 def main(screen):
     ch, first, selected, paths = 0, 0, 0, os.listdir()
@@ -2454,10 +2441,11 @@ def main(screen):
             color = A_REVERSE if filename == paths[selected] else 0
             screen.addnstr(y, 0, filename, width-1, color)
         ch = screen.getch()
-        selected += (ch == KEY_DOWN) - (ch == KEY_UP)
-        selected = max(0, min(len(paths)-1, selected))
-        first += (selected >= first + height) - (selected < first)
-        if ch in [KEY_LEFT, KEY_RIGHT, KEY_ENTER, ord('\n'), ord('\r')]:
+        selected -= (ch == KEY_UP) and (selected > 0)
+        selected += (ch == KEY_DOWN) and (selected < len(paths)-1)
+        first -= (first > selected)
+        first += (first < selected-(height-1))
+        if ch in [KEY_LEFT, KEY_RIGHT, ord('\n')]:
             new_dir = '..' if ch == KEY_LEFT else paths[selected]
             if os.path.isdir(new_dir):
                 os.chdir(new_dir)
@@ -2476,9 +2464,9 @@ GUI App
 # $ pip3 install PySimpleGUI
 import PySimpleGUI as sg
 
-text_box = sg.Input(default_text='100', enable_events=True, key='-QUANTITY-')
-dropdown = sg.InputCombo(['g', 'kg', 't'], 'kg', readonly=True, enable_events=True, k='-UNIT-')
-label    = sg.Text('100 kg is 220.462 lbs.', key='-OUTPUT-')
+text_box = sg.Input(default_text='100', enable_events=True, key='QUANTITY')
+dropdown = sg.InputCombo(['g', 'kg', 't'], 'kg', readonly=True, enable_events=True, k='UNIT')
+label    = sg.Text('100 kg is 220.462 lbs.', key='OUTPUT')
 button   = sg.Button('Close')
 window   = sg.Window('Weight Converter', [[text_box, dropdown], [label], [button]])
 
@@ -2487,13 +2475,13 @@ while True:
     if event in [sg.WIN_CLOSED, 'Close']:
         break
     try:
-        quantity = float(values['-QUANTITY-'])
+        quantity = float(values['QUANTITY'])
     except ValueError:
         continue
-    unit = values['-UNIT-']
+    unit = values['UNIT']
     factors = {'g': 0.001, 'kg': 1, 't': 1000}
     lbs = quantity * factors[unit] / 0.45359237
-    window['-OUTPUT-'].update(value=f'{quantity} {unit} is {lbs:g} lbs.')
+    window['OUTPUT'].update(value=f'{quantity} {unit} is {lbs:g} lbs.')
 window.close()
 ```
 
@@ -2510,10 +2498,9 @@ document   = bs4.BeautifulSoup(response.text, 'html.parser')
 table      = document.find('table', class_='infobox vevent')
 python_url = table.find('th', text='Website').next_sibling.a['href']
 logo_url   = table.find('img')['src']
-logo       = requests.get(f'https:{logo_url}').content
 filename   = os.path.basename(logo_url)
 with open(filename, 'wb') as file:
-    file.write(logo)
+    file.write(requests.get(f'https:{logo_url}').content)
 print(f'{python_url}, file://{os.path.abspath(filename)}')
 ```
 
@@ -2525,6 +2512,7 @@ from selenium import webdriver
 
 <WebDrv> = webdriver.Chrome/Firefox/Safari/Edge()     # Opens a browser. Also <WebDrv>.quit().
 <WebDrv>.get('<url>')                                 # Also <WebDrv>.implicitly_wait(seconds).
+<str>  = <WebDrv>.page_source                         # Returns HTML of fully rendered page.
 <El>   = <WebDrv/El>.find_element('css selector', …)  # '<tag>#<id>.<class>[<attr>="<val>"]…'.
 <list> = <WebDrv/El>.find_elements('xpath', …)        # '//<tag>[@<attr>="<val>"]…'. See XPath.
 <str>  = <El>.get_attribute(<str>)                    # Property if exists. Also <El>.text.
@@ -2553,20 +2541,20 @@ import flask as fl
 
 ```python
 app = fl.Flask(__name__)                   # Returns the app object. Put at the top.
-app.run(host=None, port=None, debug=None)  # Or: $ flask --app FILE run [--ARG[=VAL] …]
+app.run(host=None, port=None, debug=None)  # Or: $ flask --app FILE run [--ARG[=VAL]]…
 ```
 * **Starts the app at `'http://localhost:5000'`. Use `'host="0.0.0.0"'` to run externally.**
 * **Install a WSGI server like [Waitress](https://flask.palletsprojects.com/en/latest/deploying/waitress/) and a HTTP server such as [Nginx](https://flask.palletsprojects.com/en/latest/deploying/nginx/) for better security.**
 * **Debug mode restarts the app whenever script changes and displays errors in the browser.**
 
-### Static Request
+### Serving Files
 ```python
 @app.route('/img/<path:filename>')
 def serve_file(filename):
-    return fl.send_from_directory('dirname/', filename)
+    return fl.send_from_directory('DIRNAME', filename)
 ```
 
-### Dynamic Request
+### Serving HTML
 ```python
 @app.route('/<sport>')
 def serve_html(sport):
@@ -2574,10 +2562,10 @@ def serve_html(sport):
 ```
 * **`'fl.render_template(filename, <kwargs>)'` renders a file located in 'templates' dir.**
 * **`'fl.abort(<int>)'` returns error code and `'return fl.redirect(<url>)'` redirects.**
-* **`'fl.request.args[<str>]'` returns parameter from the query string (URL right of '?').**
+* **`'fl.request.args[<str>]'` returns parameter from query string (URL part right of '?').**
 * **`'fl.session[<str>] = <obj>'` stores session data. It requires secret key to be set at the startup with `'app.secret_key = <str>'`.**
 
-### REST Request
+### Serving JSON
 ```python
 @app.post('/<sport>/odds')
 def serve_json(sport):
@@ -2673,7 +2661,7 @@ import numpy as np
 ```python
 <view>  = <array>.reshape(<shape>)                      # Also `<array>.shape = <shape>`.
 <array> = <array>.flatten()                             # Also `<view> = <array>.ravel()`.
-<view>  = <array>.transpose()                           # Or: <array>.T
+<view>  = <array>.transpose()                           # Flips the table over its diagonal.
 ```
 
 ```python
@@ -2710,58 +2698,55 @@ import numpy as np
 <1/2d_arr> = <2d>[<2d/1d_bools>]                        # 1d_bools must have size of a column.
 ```
 * **`':'` returns a slice of all dimension's indices. Omitted dimensions default to `':'`.**
-* **Indices should not be tuples because Python converts `'obj[i, j]'`  to `'obj[(i, j)]'`!**
-* **Indexing with a slice and 1d array works the same as when using two slices (lines 4, 6, 7).**
+* **Python converts `'obj[i, j]'` to `'obj[(i, j)]'`. This makes `'<2d>[row_i, col_i]'` and `'<2d>[row_indices]'` indistinguishable to NumPy if tuple of two indices is passed!**
 * **`'ix_([1, 2], [3, 4])'` returns `'[[1], [2]]'` and `'[[3, 4]]'`. Due to broadcasting rules, this is the same as using `'[[1, 1], [2, 2]]'` and `'[[3, 4], [3, 4]]'`.**
 * **Any value that is broadcastable to the indexed shape can be assigned to the selection.**
 
 ### Broadcasting
 **A set of rules by which NumPy functions operate on arrays of different shapes.**
-
 ```python
-left  = [ 0.1 ,  0.6 ,  0.8 ]                           # Shape: (3,)
-right = [[0.1], [0.6], [0.8]]                           # Shape: (3, 1)
+left  = np.array([0.1,  0.6,  0.8])                     # `left.shape  == (3,)`
+right = np.array([[0.1], [0.6], [0.8]])                 # `right.shape == (3, 1)`
 ```
 
 #### 1. If array shapes differ in length, left-pad the shorter shape with ones:
 ```python
-left  = [[0.1 ,  0.6 ,  0.8]]                           # Shape: (1, 3) <- !
-right = [[0.1], [0.6], [0.8]]                           # Shape: (3, 1)
+left  = np.array([[0.1,  0.6,  0.8]])                   # `left.shape  == (1, 3)`
+right = np.array([[0.1], [0.6], [0.8]])                 # `right.shape == (3, 1)`
 ```
 
 #### 2. If any dimensions differ in size, expand the ones that have size 1 by duplicating their elements:
 ```python
-left  = [[0.1,  0.6,  0.8],                             # Shape: (3, 3) <- !
-         [0.1,  0.6,  0.8],
-         [0.1,  0.6,  0.8]]
+left  = np.array([[0.1,  0.6,  0.8],                    # `left.shape  == (3, 3)`
+                  [0.1,  0.6,  0.8],
+                  [0.1,  0.6,  0.8]])
 
-right = [[0.1,  0.1,  0.1],                             # Shape: (3, 3) <- !
-         [0.6,  0.6,  0.6],
-         [0.8,  0.8,  0.8]]
+right = np.array([[0.1,  0.1,  0.1],                    # `right.shape == (3, 3)`
+                  [0.6,  0.6,  0.6],
+                  [0.8,  0.8,  0.8]])
 ```
 
 ### Example
 #### For each point returns index of its nearest point (`[0.1, 0.6, 0.8] => [1, 2, 1]`):
 
 ```python
->>> points = np.array([0.1, 0.6, 0.8])
-[ 0.1,  0.6,  0.8 ]
->>> wrapped_points = points.reshape(3, 1)
-[[0.1], [0.6], [0.8]]
->>> distances = points - wrapped_points
-[[ 0. ,  0.5,  0.7],
- [-0.5,  0. ,  0.2],
- [-0.7, -0.2,  0. ]]
->>> distances = np.abs(distances)
-[[ 0. ,  0.5,  0.7],
- [ 0.5,  0. ,  0.2],
- [ 0.7,  0.2,  0. ]]
->>> distances[range(3), range(3)] = np.inf
-[[ inf,  0.5,  0.7],
- [ 0.5,  inf,  0.2],
- [ 0.7,  0.2,  inf]]
->>> distances.argmin(1)
-[1, 2, 1]
+>>> print(points := np.array([0.1, 0.6, 0.8]))
+[0.1  0.6  0.8]
+>>> print(wrapped_points := points.reshape(3, 1))
+[[0.1]
+ [0.6]
+ [0.8]]
+>>> print(deltas := points - wrapped_points)
+[[ 0.   0.5  0.7]
+ [-0.5  0.   0.2]
+ [-0.7 -0.2  0. ]]
+>>> deltas[range(3), range(3)] = np.inf
+>>> print(distances := np.abs(deltas))
+[[inf  0.5  0.7]
+ [0.5  inf  0.2]
+ [0.7  0.2  inf]]
+>>> print(distances.argmin(axis=1))
+[1 2 1]
 ```
 
 
@@ -2776,8 +2761,8 @@ from PIL import Image
 <Image> = Image.new('<mode>', (width, height))  # Creates new image. Also `color=<int/tuple>`.
 <Image> = Image.open(<path>)                    # Identifies format based on file's contents.
 <Image> = <Image>.convert('<mode>')             # Converts image to the new mode (see Modes).
-<Image>.save(<path>)                            # Selects format based on extension (PNG/JPG…).
-<Image>.show()                                  # Opens image in the default preview app.
+<Image>.save(<path>)                            # Accepts `quality=<int>` if extension is jpg.
+<Image>.show()                                  # Displays image in default preview app.
 ```
 
 ```python
@@ -2795,13 +2780,13 @@ from PIL import Image
 
 ```python
 <array> = np.array(<Image>)                     # Creates a 2d/3d NumPy array from the image.
-<Image> = Image.fromarray(np.uint8(<array>))    # Use `<array>.clip(0, 255)` to clip values.
+<Image> = Image.fromarray(np.uint8(<array>))    # Use <array>.clip(0, 255) to clip the values.
 ```
 
 ### Modes
-* **`'L'` - Lightness (greyscale image). Each pixel is an int between 0 and 255.**
-* **`'RGB'` - Red, green, blue (true color image). Each pixel is a tuple of three ints.**
-* **`'RGBA'` - RGB with alpha. Low alpha (i.e. forth int) makes pixels more transparent.**
+* **`'L'` - Lightness (greyscale image). Each pixel is an integer between 0 and 255.**
+* **`'RGB'` - Red, green, blue (true color image). Each pixel is a tuple of three integers.**
+* **`'RGBA'` - RGB with alpha. Low alpha (i.e. fourth int) makes pixel more transparent.**
 * **`'HSV'` - Hue, saturation, value. Three ints representing color in HSV color space.**
 
 
@@ -2829,13 +2814,13 @@ img.show()
 ```python
 from PIL import ImageDraw
 <Draw> = ImageDraw.Draw(<Image>)                # Object for adding 2D graphics to the image.
-<Draw>.point((x, y))                            # Draws a point. Truncates floats into ints.
-<Draw>.line((x1, y1, x2, y2 [, ...]))           # To get anti-aliasing use Image's resize().
+<Draw>.point((x, y))                            # Draws a point. Also `fill=<int/tuple/str>`.
+<Draw>.line((x1, y1, x2, y2 [, ...]))           # For anti-aliasing use <Image>.resize((w, h)).
 <Draw>.arc((x1, y1, x2, y2), deg1, deg2)        # Draws in clockwise dir. Also pieslice().
-<Draw>.rectangle((x1, y1, x2, y2))              # To rotate use Image's rotate() and paste().
-<Draw>.polygon((x1, y1, x2, y2, ...))           # Last point gets connected to the first.
-<Draw>.ellipse((x1, y1, x2, y2))                # Also rounded_rectangle(), regular_polygon().
-<Draw>.text((x, y), <str>, font=<Font>)         # `<Font> = ImageFont.truetype(<path>, size)`
+<Draw>.rectangle((x1, y1, x2, y2))              # Also rounded_rectangle(), regular_polygon().
+<Draw>.polygon((x1, y1, x2, y2, ...))           # Last point gets connected to the first one.
+<Draw>.ellipse((x1, y1, x2, y2))                # To rotate use <Image>.rotate(anticlock_deg).
+<Draw>.text((x, y), <str>, font=<Font>)         # `<Font> = ImageFont.truetype(<path>, size)`.
 ```
 * **Use `'fill=<color>'` to set the primary color.**
 * **Use `'width=<int>'` to set the width of lines or contours.**
@@ -2876,7 +2861,7 @@ import wave
 <int>   = <Wave>.getnchannels()       # Returns number of samples per frame.
 <int>   = <Wave>.getsampwidth()       # Returns number of bytes per sample.
 <tuple> = <Wave>.getparams()          # Returns namedtuple of all parameters.
-<bytes> = <Wave>.readframes(nframes)  # Returns next n frames. All if -1.
+<bytes> = <Wave>.readframes(nframes)  # Returns all frames if -1 is passed.
 ```
 
 ```python
@@ -2913,7 +2898,7 @@ def read_wav_file(filename):
         p = file.getparams()
         frames = file.readframes(-1)
     bytes_samples = (frames[i : i + p.sampwidth] for i in range(0, len(frames), p.sampwidth))
-    return [get_int(b) / pow(2, p.sampwidth * 8 - 1) for b in bytes_samples], p
+    return [get_int(b) / pow(2, (p.sampwidth * 8) - 1) for b in bytes_samples], p
 ```
 
 ### Write Float Samples to WAV File
@@ -2921,8 +2906,8 @@ def read_wav_file(filename):
 def write_to_wav_file(filename, samples_f, p=None, nchannels=1, sampwidth=2, framerate=44100):
     def get_bytes(a_float):
         a_float = max(-1, min(1 - 2e-16, a_float))
-        a_float += p.sampwidth == 1
-        a_float *= pow(2, p.sampwidth * 8 - 1)
+        a_float += (p.sampwidth == 1)
+        a_float *= pow(2, (p.sampwidth * 8) - 1)
         return int(a_float).to_bytes(p.sampwidth, 'little', signed=(p.sampwidth != 1))
     if p is None:
         p = wave._wave_params(nchannels, sampwidth, framerate, 0, 'NONE', 'not compressed')
@@ -2944,7 +2929,7 @@ write_to_wav_file('test.wav', samples_f)
 from random import uniform
 samples_f, params = read_wav_file('test.wav')
 samples_f = (f + uniform(-0.05, 0.05) for f in samples_f)
-write_to_wav_file('test.wav', samples_f, params)
+write_to_wav_file('test.wav', samples_f, p=params)
 ```
 
 #### Plays the WAV file:
@@ -2952,8 +2937,7 @@ write_to_wav_file('test.wav', samples_f, params)
 # $ pip3 install simpleaudio
 from simpleaudio import play_buffer
 with wave.open('test.wav') as file:
-    p = file.getparams()
-    frames = file.readframes(-1)
+    frames, p = file.readframes(-1), file.getparams()
     play_buffer(frames, p.nchannels, p.sampwidth, p.framerate).wait_done()
 ```
 
@@ -2972,25 +2956,27 @@ Synthesizer
 #### Plays Popcorn by Gershon Kingsley:
 ```python
 # $ pip3 install simpleaudio
-import array, itertools as it, math, simpleaudio
+import itertools as it, math, array, simpleaudio
 
-F  = 44100
-P1 = '71♩,69♪,,71♩,66♪,,62♩,66♪,,59♩,,,71♩,69♪,,71♩,66♪,,62♩,66♪,,59♩,,,'
-P2 = '71♩,73♪,,74♩,73♪,,74♪,,71♪,,73♩,71♪,,73♪,,69♪,,71♩,69♪,,71♪,,67♪,,71♩,,,'
-get_pause   = lambda seconds: it.repeat(0, int(seconds * F))
-sin_f       = lambda i, hz: math.sin(i * 2 * math.pi * hz / F)
-get_wave    = lambda hz, seconds: (sin_f(i, hz) for i in range(int(seconds * F)))
-get_hz      = lambda note: 440 * 2 ** ((int(note[:2]) - 69) / 12)
-get_sec     = lambda note: 1/4 if '♩' in note else 1/8
-get_samples = lambda note: get_wave(get_hz(note), get_sec(note)) if note else get_pause(1/8)
-samples_f   = it.chain.from_iterable(get_samples(n) for n in (P1+P2).split(','))
-samples_i   = array.array('h', (int(f * 30000) for f in samples_f))
-simpleaudio.play_buffer(samples_i, 1, 2, F).wait_done()
+def play_notes(notes, bpm=132, f=44100):
+    get_pause   = lambda n_beats: it.repeat(0, int(n_beats * 60/bpm * f))
+    sin_f       = lambda i, hz: math.sin(i * 2 * math.pi * hz / f)
+    get_wave    = lambda hz, n_beats: (sin_f(i, hz) for i in range(int(n_beats * 60/bpm * f)))
+    get_hz      = lambda note: 440 * 2 ** ((int(note[:2]) - 69) / 12)
+    get_nbeats  = lambda note: 1/2 if '♩' in note else 1/4 if '♪' in note else 1
+    get_samples = lambda n: get_wave(get_hz(n), get_nbeats(n)) if n else get_pause(1/4)
+    samples_f   = it.chain.from_iterable(get_samples(n) for n in notes.split(','))
+    samples_i   = array.array('h', (int(fl * 5000) for fl in samples_f))
+    simpleaudio.play_buffer(samples_i, 1, 2, f).wait_done()
+
+play_notes('83♩,81♪,,83♪,,78♪,,74♪,,78♪,,71♪,,,,83♪,,81♪,,83♪,,78♪,,74♪,,78♪,,71♪,,,,'
+           '83♩,85♪,,86♪,,85♪,,86♪,,83♪,,85♩,83♪,,85♪,,81♪,,83♪,,81♪,,83♪,,79♪,,83♪,,,,')
 ```
 
 
 Pygame
 ------
+#### Opes a window and draws a square that can be moved with arrow keys:
 ```python
 # $ pip3 install pygame
 import pygame as pg
@@ -2999,27 +2985,28 @@ pg.init()
 screen = pg.display.set_mode((500, 500))
 rect = pg.Rect(240, 240, 20, 20)
 while not pg.event.get(pg.QUIT):
-    deltas = {pg.K_UP: (0, -20), pg.K_RIGHT: (20, 0), pg.K_DOWN: (0, 20), pg.K_LEFT: (-20, 0)}
     for event in pg.event.get(pg.KEYDOWN):
-        dx, dy = deltas.get(event.key, (0, 0))
-        rect = rect.move((dx, dy))
+        dx = (event.key == pg.K_RIGHT) - (event.key == pg.K_LEFT)
+        dy = (event.key == pg.K_DOWN) - (event.key == pg.K_UP)
+        rect = rect.move((dx * 20, dy * 20))
     screen.fill(pg.Color('black'))
     pg.draw.rect(screen, pg.Color('white'), rect)
     pg.display.flip()
+pg.quit()
 ```
 
-### Rectangle
+### Rect
 **Object for storing rectangular coordinates.**
 ```python
-<Rect> = pg.Rect(x, y, width, height)           # Floats get truncated into ints.
-<int>  = <Rect>.x/y/centerx/centery/…           # Top, right, bottom, left. Allows assignments.
-<tup.> = <Rect>.topleft/center/…                # Topright, bottomright, bottomleft. Same.
-<Rect> = <Rect>.move((delta_x, delta_y))        # Use move_ip() to move in-place.
+<Rect> = pg.Rect(x, y, width, height)           # Creates Rect object. Truncates passed floats.
+<int>  = <Rect>.x/y/centerx/centery/…           # `top/right/bottom/left`. Allows assignments.
+<tup.> = <Rect>.topleft/center/…                # `topright/bottomright/bottomleft/size`. Same.
+<Rect> = <Rect>.move((delta_x, delta_y))        # Use move_ip() to move the rectangle in-place.
 ```
 
 ```python
-<bool> = <Rect>.collidepoint((x, y))            # Checks if rectangle contains the point.
-<bool> = <Rect>.colliderect(<Rect>)             # Checks if the two rectangles overlap.
+<bool> = <Rect>.collidepoint((x, y))            # Checks whether rectangle contains the point.
+<bool> = <Rect>.colliderect(<Rect>)             # Checks whether the two rectangles overlap.
 <int>  = <Rect>.collidelist(<list_of_Rect>)     # Returns index of first colliding Rect or -1.
 <list> = <Rect>.collidelistall(<list_of_Rect>)  # Returns indices of all colliding rectangles.
 ```
@@ -3027,7 +3014,7 @@ while not pg.event.get(pg.QUIT):
 ### Surface
 **Object for representing images.**
 ```python
-<Surf> = pg.display.set_mode((width, height))   # Opens new window and returns its surface.
+<Surf> = pg.display.set_mode((width, height))   # Opens a new window and returns its surface.
 <Surf> = pg.Surface((width, height))            # New RGB surface. RGBA if `flags=pg.SRCALPHA`.
 <Surf> = pg.image.load(<path/file>)             # Loads the image. Format depends on source.
 <Surf> = pg.surfarray.make_surface(<np_array>)  # Also `<np_arr> = surfarray.pixels3d(<Surf>)`.
@@ -3035,35 +3022,34 @@ while not pg.event.get(pg.QUIT):
 ```
 
 ```python
-<Surf>.fill(color)                              # Tuple, Color('#rrggbb[aa]') or Color(<name>).
+<Surf>.fill(color)                              # Pass tuple of ints or pg.Color('<name/hex>').
 <Surf>.set_at((x, y), color)                    # Updates pixel. Also <Surf>.get_at((x, y)).
 <Surf>.blit(<Surf>, (x, y))                     # Draws passed surface at specified location.
 ```
 
 ```python
-from pygame.transform import scale, ...
-<Surf> = scale(<Surf>, (width, height))         # Returns scaled surface.
-<Surf> = rotate(<Surf>, anticlock_degrees)      # Returns rotated and scaled surface.
-<Surf> = flip(<Surf>, x_bool, y_bool)           # Returns flipped surface.
+from pygame.transform import scale, rotate      # Also: flip, smoothscale, scale_by.
+<Surf> = scale(<Surf>, (width, height))         # Scales the surface. `smoothscale()` blurs it.
+<Surf> = rotate(<Surf>, angle)                  # Rotates the surface for counterclock degrees.
+<Surf> = flip(<Surf>, flip_x=False)             # Mirrors the surface. Also `flip_y=False`.
 ```
 
 ```python
-from pygame.draw import line, ...
-line(<Surf>, color, (x1, y1), (x2, y2), width)  # Draws a line to the surface.
+from pygame.draw import line, arc, rect         # Also: ellipse, polygon, circle, aaline.
+line(<Surf>, color, (x1, y1), (x2, y2))         # Draws a line to the surface. Also `width=1`.
 arc(<Surf>, color, <Rect>, from_rad, to_rad)    # Also ellipse(<Surf>, color, <Rect>, width=0).
 rect(<Surf>, color, <Rect>, width=0)            # Also polygon(<Surf>, color, points, width=0).
 ```
 
-### Font
 ```python
 <Font> = pg.font.Font(<path/file>, size)        # Loads TTF file. Pass None for default font.
-<Surf> = <Font>.render(text, antialias, color)  # Background color can be specified at the end.
+<Surf> = <Font>.render(text, antialias, color)  # Accepts background color as fourth argument.
 ```
 
 ### Sound
 ```python
 <Sound> = pg.mixer.Sound(<path/file/bytes>)     # WAV file or bytes/array of signed shorts.
-<Sound>.play/stop()                             # Also set_volume(<float>), fadeout(msec).
+<Sound>.play/stop()                             # Also set_volume(<float>) and fadeout(msec).
 ```
 
 ### Basic Mario Brothers Example
@@ -3097,19 +3083,19 @@ def main():
 def run(screen, images, mario, tiles):
     clock = pg.time.Clock()
     pressed = set()
-    while not pg.event.get(pg.QUIT) and clock.tick(28):
-        keys = {pg.K_UP: D.n, pg.K_RIGHT: D.e, pg.K_DOWN: D.s, pg.K_LEFT: D.w}
-        pressed |= {keys.get(e.key) for e in pg.event.get(pg.KEYDOWN)}
-        pressed -= {keys.get(e.key) for e in pg.event.get(pg.KEYUP)}
+    while not pg.event.get(pg.QUIT):
+        clock.tick(28)
+        pressed |= {e.key for e in pg.event.get(pg.KEYDOWN)}
+        pressed -= {e.key for e in pg.event.get(pg.KEYUP)}
         update_speed(mario, tiles, pressed)
         update_position(mario, tiles)
         draw(screen, images, mario, tiles)
 
 def update_speed(mario, tiles, pressed):
     x, y = mario.spd
-    x += 2 * ((D.e in pressed) - (D.w in pressed))
+    x += 2 * ((pg.K_RIGHT in pressed) - (pg.K_LEFT in pressed))
     x += (x < 0) - (x > 0)
-    y += 1 if D.s not in get_boundaries(mario.rect, tiles) else (D.n in pressed) * -10
+    y += 1 if D.s not in get_boundaries(mario.rect, tiles) else (pg.K_UP in pressed) * -10
     mario.spd = P(x=max(-MAX_S.x, min(MAX_S.x, x)), y=max(-MAX_S.y, min(MAX_S.y, y)))
 
 def update_position(mario, tiles):
@@ -3132,7 +3118,7 @@ def draw(screen, images, mario, tiles):
     screen.fill((85, 168, 255))
     mario.facing_left = mario.spd.x < 0 if mario.spd.x else mario.facing_left
     is_airborne = D.s not in get_boundaries(mario.rect, tiles)
-    image_index = 4 if is_airborne else (next(mario.frame_cycle) if mario.spd.x else 6)
+    image_index = 4 if is_airborne else next(mario.frame_cycle) if mario.spd.x else 6
     screen.blit(images[image_index + (mario.facing_left * 9)], mario.rect)
     for t in tiles:
         is_border = t.x in [0, (W-1)*16] or t.y in [0, (H-1)*16]
@@ -3146,7 +3132,7 @@ if __name__ == '__main__':
 
 Pandas
 ------
-**Data analysis library. For examples see [Plotly](#displays-a-line-chart-of-total-coronavirus-deaths-per-million-grouped-by-continent).**
+**Data analysis library. For examples see [Plotly](#plotly).**
 
 ```python
 # $ pip3 install pandas matplotlib
@@ -3164,9 +3150,8 @@ Name: a, dtype: int64
 ```
 
 ```python
-<S>  = pd.Series(<list>)                       # Assigns RangeIndex starting at 0.
-<S>  = pd.Series(<dict>)                       # Takes dictionary's keys for index.
-<S>  = pd.Series(<dict/Series>, index=<list>)  # Only keeps items with keys specified in index.
+<S>  = pd.Series(<list>)                       # Uses list's indices for 'index'.
+<S>  = pd.Series(<dict>)                       # Uses dictionary's keys for 'index'.
 ```
 
 ```python
@@ -3178,30 +3163,33 @@ Name: a, dtype: int64
 ```python
 <el> = <S>[key/i]                              # Or: <S>.<key>
 <S>  = <S>[coll_of_keys/coll_of_i]             # Or: <S>[key/i : key/i]
-<S>  = <S>[bools]                              # Or: <S>.loc/iloc[bools]
+<S>  = <S>[<S_of_bools>]                       # Or: <S>.loc/iloc[<S_of_bools>]
 ```
 
 ```python
-<S>  = <S> > <el/S>                            # Returns a Series of bools.
+<S>  = <S> > <el/S>                            # Returns S of bools. For logic use &, |, ~.
 <S>  = <S> + <el/S>                            # Items with non-matching keys get value NaN.
 ```
 
 ```python
-<S> = pd.concat(<coll_of_S>)                   # Concats multiple series into one long Series.
-<S> = <S>.combine_first(<S>)                   # Adds items that are not yet present.
-<S>.update(<S>)                                # Updates items that are already present.
+<S>  = <S>.head/describe/sort_values()         # Also <S>.unique/value_counts/round/dropna().
+<S>  = <S>.str.strip/lower/contains/replace()  # Also split().str[i] or split(expand=True).
+<S>  = <S>.dt.year/month/day/hour              # Use pd.to_datetime(<S>) to get S of datetimes.
+<S>  = <S>.dt.to_period('y/m/d/h')             # Quantizes datetimes into Period objects.
 ```
 
 ```python
-<S>.plot.line/area/bar/pie/hist()              # Generates a Matplotlib plot.
+<S>.plot.line/area/bar/pie/hist()              # Generates a plot. Accepts `title=<str>`.
 plt.show()                                     # Displays the plot. Also plt.savefig(<path>).
 ```
-* **Indexing objects can't be tuples because `'obj[x, y]'` is converted to `'obj[(x, y)]'`!**
-* **Pandas uses NumPy types like `'np.int64'`. Series is converted to `'float64'` if we assign np.nan to any item. Use `'<S>.astype(<str/type>)'` to get converted Series.**
+* **Use `'print(<S>.to_string())'` to print a Series that has more than sixty items.**
+* **Use `'<S>.index'` to get collection of keys and `'<S>.index = <coll>'` to update them.**
+* **Only pass a list or Series to loc/iloc because `'obj[x, y]'` is converted to `'obj[(x, y)]'` and `'<S>.loc[key_1, key_2]'` is how you retrieve a value from a multi-indexed Series.**
+* **Pandas uses NumPy types like `'np.int64'`. Series is converted to `'float64'` if np.nan is assigned to any item. Use `'<S>.astype(<str/type>)'` to get converted Series.**
 
 #### Series — Aggregate, Transform, Map:
 ```python
-<el> = <S>.sum/max/mean/idxmax/all()           # Or: <S>.agg(lambda <S>: <el>)
+<el> = <S>.sum/max/mean/std/idxmax/count()     # Or: <S>.agg(lambda <S>: <el>)
 <S>  = <S>.rank/diff/cumsum/ffill/interpol…()  # Or: <S>.agg/transform(lambda <S>: <S>)
 <S>  = <S>.isna/fillna/isin([<el/coll>])       # Or: <S>.agg/transform/map(lambda <el>: <el>)
 ```
@@ -3224,14 +3212,12 @@ plt.show()                                     # Displays the plot. Also plt.sav
 |              |    y  2.0   |   y   2.0   |      y  2.0   |
 +--------------+-------------+-------------+---------------+
 ```
-* **Methods ffill(), interpolate(), fillna() and dropna() accept `'inplace=True'`.**
-* **Last result has a multi-index. Use `'<S>[key_1, key_2]'` to get its values.**
 
 ### DataFrame
 **Table with labeled rows and columns.**
 
 ```python
->>> l = pd.DataFrame([[1, 2], [3, 4]], index=['a', 'b'], columns=['x', 'y']); l
+>>> df = pd.DataFrame([[1, 2], [3, 4]], index=['a', 'b'], columns=['x', 'y']); df
    x  y
 a  1  2
 b  3  4
@@ -3251,12 +3237,12 @@ b  3  4
 
 ```python
 <S/DF> = <DF>[col_key/s]                       # Or: <DF>.<col_key>
-<DF>   = <DF>[row_bools]                       # Keeps rows as specified by bools.
+<DF>   = <DF>[<S_of_bools>]                    # Filters rows. For example `df[df.x > 1]`.
 <DF>   = <DF>[<DF_of_bools>]                   # Assigns NaN to items that are False in bools.
 ```
 
 ```python
-<DF>   = <DF> > <el/S/DF>                      # Returns DF of bools. S is treated as a row.
+<DF>   = <DF> > <el/S/DF>                      # Returns DF of bools. Treats series as a row.
 <DF>   = <DF> + <el/S/DF>                      # Items with non-matching keys get value NaN.
 ```
 
@@ -3268,120 +3254,121 @@ b  3  4
 ```
 
 ```python
-<DF>   = <DF>.head/tail/sample(<int>)          # Returns first, last, or random n elements.
-<DF>   = <DF>.describe()                       # Describes columns. Also shape, info(), corr().
-<DF>   = <DF>.query('<query>')                 # Filters rows with e.g. 'col_1 == val_1 and …'.
+<DF>   = <DF>.head/tail/sample(<int>)          # Returns first, last, or random n rows.
+<DF>   = <DF>.describe()                       # Describes columns. Also info(), corr(), shape.
+<DF>   = <DF>.query('<query>')                 # Filters rows. For example `df.query('x > 1')`.
 ```
 
 ```python
-<DF>.plot.line/area/bar/scatter(x=col_key, …)  # `y=col_key/s`. Also hist/box(by=col_key).
+<DF>.plot.line/area/bar/scatter(x=col_key, …)  # `y=col_key/s`. Also hist/box(column/by=col_k).
 plt.show()                                     # Displays the plot. Also plt.savefig(<path>).
 ```
 
 #### DataFrame — Merge, Join, Concat:
 ```python
->>> r = pd.DataFrame([[4, 5], [6, 7]], index=['b', 'c'], columns=['y', 'z']); r
+>>> df_2 = pd.DataFrame([[4, 5], [6, 7]], index=['b', 'c'], columns=['y', 'z']); df_2
    y  z
 b  4  5
 c  6  7
 ```
 
 ```text
-+------------------------+---------------+------------+------------+--------------------------+
-|                        |    'outer'    |   'inner'  |   'left'   |       Description        |
-+------------------------+---------------+------------+------------+--------------------------+
-| l.merge(r, on='y',     |    x   y   z  | x   y   z  | x   y   z  | Merges on column if 'on' |
-|            how=…)      | 0  1   2   .  | 3   4   5  | 1   2   .  | or 'left/right_on' are   |
-|                        | 1  3   4   5  |            | 3   4   5  | set, else on shared cols.|
-|                        | 2  .   6   7  |            |            | Uses 'inner' by default. |
-+------------------------+---------------+------------+------------+--------------------------+
-| l.join(r, lsuffix='l', |    x yl yr  z |            | x yl yr  z | Merges on row keys.      |
-|           rsuffix='r', | a  1  2  .  . | x yl yr  z | 1  2  .  . | Uses 'left' by default.  |
-|           how=…)       | b  3  4  4  5 | 3  4  4  5 | 3  4  4  5 | If r is a Series, it is  |
-|                        | c  .  .  6  7 |            |            | treated as a column.     |
-+------------------------+---------------+------------+------------+--------------------------+
-| pd.concat([l, r],      |    x   y   z  |     y      |            | Adds rows at the bottom. |
-|           axis=0,      | a  1   2   .  |     2      |            | Uses 'outer' by default. |
-|           join=…)      | b  3   4   .  |     4      |            | A Series is treated as a |
-|                        | b  .   4   5  |     4      |            | column. To add a row use |
-|                        | c  .   6   7  |     6      |            | pd.concat([l, DF([s])]). |
-+------------------------+---------------+------------+------------+--------------------------+
-| pd.concat([l, r],      |    x  y  y  z |            |            | Adds columns at the      |
-|           axis=1,      | a  1  2  .  . | x  y  y  z |            | right end. Uses 'outer'  |
-|           join=…)      | b  3  4  4  5 | 3  4  4  5 |            | by default. A Series is  |
-|                        | c  .  .  6  7 |            |            | treated as a column.     |
-+------------------------+---------------+------------+------------+--------------------------+
++-----------------------+---------------+------------+------------+---------------------------+
+|                       |    'outer'    |   'inner'  |   'left'   |       Description         |
++-----------------------+---------------+------------+------------+---------------------------+
+| df.merge(df_2,        |    x   y   z  | x   y   z  | x   y   z  | Merges on column if 'on'  |
+|          on='y',      | 0  1   2   .  | 3   4   5  | 1   2   .  | or 'left_on/right_on' are |
+|          how=…)       | 1  3   4   5  |            | 3   4   5  | set, else on shared cols. |
+|                       | 2  .   6   7  |            |            | Uses 'inner' by default.  |
++-----------------------+---------------+------------+------------+---------------------------+
+| df.join(df_2,         |    x yl yr  z |            | x yl yr  z | Merges on row keys.       |
+|         lsuffix='l',  | a  1  2  .  . | x yl yr  z | 1  2  .  . | Uses 'left' by default.   |
+|         rsuffix='r',  | b  3  4  4  5 | 3  4  4  5 | 3  4  4  5 | If Series is passed, it   |
+|         how=…)        | c  .  .  6  7 |            |            | is treated as a column.   |
++-----------------------+---------------+------------+------------+---------------------------+
+| pd.concat([df, df_2], |    x   y   z  |     y      |            | Adds rows at the bottom.  |
+|           axis=0,     | a  1   2   .  |     2      |            | Uses 'outer' by default.  |
+|           join=…)     | b  3   4   .  |     4      |            | A Series is treated as a  |
+|                       | b  .   4   5  |     4      |            | column. To add a row use  |
+|                       | c  .   6   7  |     6      |            | pd.concat([df, DF([s])]). |
++-----------------------+---------------+------------+------------+---------------------------+
+| pd.concat([df, df_2], |    x  y  y  z |            |            | Adds columns at the       |
+|           axis=1,     | a  1  2  .  . | x  y  y  z |            | right end. Uses 'outer'   |
+|           join=…)     | b  3  4  4  5 | 3  4  4  5 |            | by default. A Series is   |
+|                       | c  .  .  6  7 |            |            | treated as a column.      |
++-----------------------+---------------+------------+------------+---------------------------+
 ```
 
 #### DataFrame — Aggregate, Transform, Map:
 ```python
-<S>  = <DF>.sum/max/mean/idxmax/all()          # Or: <DF>.apply/agg(lambda <S>: <el>)
+<S>  = <DF>.sum/max/mean/std/idxmax/count()    # Or: <DF>.apply/agg(lambda <S>: <el>)
 <DF> = <DF>.rank/diff/cumsum/ffill/interpo…()  # Or: <DF>.apply/agg/transform(lambda <S>: <S>)
-<DF> = <DF>.isna/fillna/isin([<el/coll>])      # Or: <S>.agg/transform/map(lambda <el>: <el>)
+<DF> = <DF>.isna/fillna/isin([<el/coll>])      # Or: <DF>.applymap(lambda <el>: <el>)
 ```
 
 ```text
-+----------------+---------------+---------------+---------------+
-|                |     'sum'     |    ['sum']    | {'x': 'sum'}  |
-+----------------+---------------+---------------+---------------+
-| l.apply(…)     |      x  4     |        x  y   |     x  4      |
-| l.agg(…)       |      y  6     |   sum  4  6   |               |
-+----------------+---------------+---------------+---------------+
++-----------------+---------------+---------------+---------------+
+|                 |     'sum'     |    ['sum']    | {'x': 'sum'}  |
++-----------------+---------------+---------------+---------------+
+| df.apply(…)     |      x  4     |        x  y   |     x  4      |
+| df.agg(…)       |      y  6     |   sum  4  6   |               |
++-----------------+---------------+---------------+---------------+
 ```
 
 ```text
-+----------------+---------------+---------------+---------------+
-|                |     'rank'    |    ['rank']   | {'x': 'rank'} |
-+----------------+---------------+---------------+---------------+
-| l.apply(…)     |               |       x    y  |               |
-| l.agg(…)       |       x    y  |    rank rank  |         x     |
-| l.transform(…) |  a  1.0  1.0  |  a  1.0  1.0  |    a  1.0     |
-|                |  b  2.0  2.0  |  b  2.0  2.0  |    b  2.0     |
-+----------------+---------------+---------------+---------------+
++-----------------+---------------+---------------+---------------+
+|                 |     'rank'    |    ['rank']   | {'x': 'rank'} |
++-----------------+---------------+---------------+---------------+
+| df.apply(…)     |               |       x    y  |               |
+| df.agg(…)       |       x    y  |    rank rank  |         x     |
+| df.transform(…) |  a  1.0  1.0  |  a  1.0  1.0  |    a  1.0     |
+|                 |  b  2.0  2.0  |  b  2.0  2.0  |    b  2.0     |
++-----------------+---------------+---------------+---------------+
 ```
-* **All methods operate on columns by default. Pass `'axis=1'` to process the rows instead.**
-* **Fifth result's columns are indexed with a multi-index. This means we need a tuple of column keys to specify a single column: `'<DF>.loc[row_k, (col_k_1, col_k_2)]'`.**
+* **Listed methods process the columns unless they receive `'axis=1'`. Exceptions to this rule are `'<DF>.dropna()'`, `'<DF>.drop(row_key/s)'` and `'<DF>.rename(<dict/func>)'`.**
+* **Fifth result's columns are indexed with a multi-index. This means we need a tuple of column keys to specify a column: `'<DF>.loc[row_key, (col_key_1, col_key_2)]'`.**
 
-#### DataFrame — Multi-Index:
+### Multi-Index
 ```python
-<DF>   = <DF>.xs(row_key, level=<int>)         # Rows with key on passed level of multi-index.
-<DF>   = <DF>.xs(row_keys, level=<ints>)       # Rows that have first key on first level, etc.
-<DF>   = <DF>.set_index(col_keys)              # Combines multiple columns into a multi-index.
-<S/DF> = <DF>.stack/unstack(level=-1)          # Combines col keys with row keys or vice versa.
-<DF>   = <DF>.pivot_table(index=col_key/s, …)  # `columns=col_key/s, values=col_key/s`.
+<DF> = <DF>.loc[row_key_1]                     # Or: <DF>.xs(row_key_1)
+<DF> = <DF>.loc[:, (slice(None), col_key_2)]   # Or: <DF>.xs(col_key_2, axis=1, level=1)
+<DF> = <DF>.set_index(col_keys)                # Creates index from cols. Also `append=False`.
+<DF> = <DF>.pivot_table(index=col_key/s)       # `columns=key/s, values=key/s, aggfunc='mean'`.
+<S>  = <DF>.stack/unstack(level=-1)            # Combines col keys with row keys or vice versa.
 ```
 
-#### DataFrame — Encode, Decode:
+### File Formats
 ```python
-<DF> = pd.read_json/html('<str/path/url>')     # Run `$ pip3 install beautifulsoup4 lxml`.
-<DF> = pd.read_csv('<path/url>')               # `header/index_col/dtype/usecols/…=<obj>`.
-<DF> = pd.read_pickle/excel('<path/url>')      # Use `sheet_name=None` to get all Excel sheets.
-<DF> = pd.read_sql('<table/query>', <conn.>)   # SQLite3/SQLAlchemy connection (see #SQLite).
+<S/DF> = pd.read_json/pickle(<path/url/file>)  # Also io.StringIO(<str>), io.BytesIO(<bytes>).
+<DF>   = pd.read_csv/excel(<path/url/file>)    # Also `header/index_col/dtype/usecols/…=<obj>`.
+<list> = pd.read_html(<path/url/file>)         # Raises ImportError if webpage has zero tables.
+<S/DF> = pd.read_parquet/feather/hdf(<path…>)  # Function read_hdf() accepts `key=<s/df_name>`.
+<DF>   = pd.read_sql('<table/query>', <conn>)  # Pass SQLite3/Alchemy connection. See #SQLite.
 ```
 
 ```python
-<dict> = <DF>.to_dict('d/l/s/…')               # Returns columns as dicts, lists or series.
-<str>  = <DF>.to_json/html/csv/latex()         # Saves output to a file if path is passed.
-<DF>.to_pickle/excel(<path>)                   # Run `$ pip3 install "pandas[excel]" odfpy`.
+<DF>.to_json/csv/html/latex/parquet(<path>)    # Returns a string/bytes if path is omitted.
+<DF>.to_pickle/excel/feather/hdf(<path>)       # Method to_hdf() requires `key=<s/df_name>`.
 <DF>.to_sql('<table_name>', <connection>)      # Also `if_exists='fail/replace/append'`.
 ```
-* **Read\_csv() only parses dates of columns that were specified by 'parse\_dates' argument. It automatically tries to detect the format, but it can be helped with 'date\_format' or 'datefirst' arguments. Both dates and datetimes get stored as pd.Timestamp objects.**
-* **If there's a single invalid date then it returns the whole column as a series of strings, unlike `'<S> = pd.to_datetime(<S>, errors="coerce")'`, which uses pd.NaT.**
-* **To get specific attributes from a series of Timestamps use `'<S>.dt.year/date/…'`.**
+* **`'$ pip3 install "pandas[excel]" odfpy lxml pyarrow'` installs dependencies.**
+* **Csv functions use the same dialect as standard library's csv module (e.g. `'sep=","'`).**
+* **Read\_csv() only parses dates of columns that are listed in 'parse\_dates'. It automatically tries to detect the format, but it can be helped with 'date\_format' or 'dayfirst' arguments.**
+* **We get a dataframe with DatetimeIndex if 'parse_dates' argument includes 'index\_col'. Its `'resample("y/m/d/h")'` method returns Resampler object that is similar to GroupBy.**
 
 ### GroupBy
 **Object that groups together rows of a dataframe based on the value of the passed column.**
 
 ```python
 <GB> = <DF>.groupby(col_key/s)                 # Splits DF into groups based on passed column.
-<DF> = <GB>.apply(<func>)                      # Maps each group. Func can return DF, S or el.
+<DF> = <GB>.apply/filter(<func>)               # Filter drops a group if func returns False.
 <DF> = <GB>.get_group(<el>)                    # Selects a group by grouping column's value.
 <S>  = <GB>.size()                             # S of group sizes. Same keys as get_group().
 <GB> = <GB>[col_key]                           # Single column GB. All operations return S.
 ```
 
 ```python
-<DF> = <GB>.sum/max/mean/idxmax/all()          # Or: <GB>.agg(lambda <S>: <el>)
+<DF> = <GB>.sum/max/mean/std/idxmax/count()    # Or: <GB>.agg(lambda <S>: <el>)
 <DF> = <GB>.rank/diff/cumsum/ffill()           # Or: <GB>.transform(lambda <S>: <S>)
 <DF> = <GB>.fillna(<el>)                       # Or: <GB>.transform(lambda <S>: <S>)
 ```
@@ -3407,7 +3394,7 @@ z
 
 ```python
 <RS/RDF/RGB> = <S/DF/GB>.rolling(win_size)     # Also: `min_periods=None, center=False`.
-<RS/RDF/RGB> = <RDF/RGB>[col_key/s]            # Or: <RDF/RGB>.col_key
+<RS/RDF/RGB> = <RDF/RGB>[col_key/s]            # Or: <RDF/RGB>.<col_key>
 <S/DF>       = <R>.mean/sum/max()              # Or: <R>.apply/agg(<agg_func/str>)
 ```
 
@@ -3420,19 +3407,19 @@ import plotly.express as px, pandas as pd
 ```
 
 ```python
-<Fig> = px.line(<DF>, x=col_key, y=col_key)            # Or: px.line(x=<list>, y=<list>)
-<Fig>.update_layout(margin=dict(t=0, r=0, b=0, l=0))   # Also `paper_bgcolor='rgb(0, 0, 0)'`.
-<Fig>.write_html/json/image('<path>')                  # Also <Fig>.show().
+<Fig> = px.line(<DF> [, y=col_key/s [, x=col_key]])   # Also px.line(y=<list> [, x=<list>]).
+<Fig>.update_layout(paper_bgcolor='#rrggbb')          # Also `margin=dict(t=0, r=0, b=0, l=0)`.
+<Fig>.write_html/json/image('<path>')                 # Use <Fig>.show() to display the plot.
 ```
 
 ```python
-<Fig> = px.area/bar/box(<DF>, x=col_key, y=col_key)    # Also `color=col_key`.
-<Fig> = px.scatter(<DF>, x=col_key, y=col_key)         # Also `color/size/symbol=col_key`.
-<Fig> = px.scatter_3d(<DF>, x=col_key, y=col_key, …)   # `z=col_key`. Also color/size/symbol.
-<Fig> = px.histogram(<DF>, x=col_key [, nbins=<int>])  # Number of bins depends on DF size.
+<Fig> = px.area/bar/box(<DF>, x=col_key, y=col_keys)  # Also `color=col_key`. All are optional.
+<Fig> = px.scatter(<DF>, x=col_key, y=col_keys)       # Also `color/size/symbol=col_key`. Same.
+<Fig> = px.scatter_3d(<DF>, x=col_key, y=col_key, …)  # `z=col_key`. Also color, size, symbol.
+<Fig> = px.histogram(<DF>, x=col_keys, y=col_key)     # Also color, nbins. All are optional.
 ```
 
-#### Displays a line chart of total coronavirus deaths per million grouped by continent:
+#### Displays a line chart of total COVID-19 deaths per million grouped by continent:
 
 ![Covid Deaths](web/covid_deaths.png)
 <div id="2a950764-39fc-416d-97fe-0a6226a3095f" class="plotly-graph-div" style="height:312px; width:914px;"></div>
@@ -3440,7 +3427,7 @@ import plotly.express as px, pandas as pd
 ```python
 covid = pd.read_csv('https://raw.githubusercontent.com/owid/covid-19-data/8dde8ca49b'
                     '6e648c17dd420b2726ca0779402651/public/data/owid-covid-data.csv',
-                    usecols=['iso_code', 'date', 'total_deaths', 'population'])
+                    usecols=['iso_code', 'date', 'population', 'total_deaths'])
 continents = pd.read_csv('https://gto76.github.io/python-cheatsheet/web/continents.csv',
                          usecols=['Three_Letter_Country_Code', 'Continent_Name'])
 df = pd.merge(covid, continents, left_on='iso_code', right_on='Three_Letter_Country_Code')
@@ -3448,41 +3435,50 @@ df = df.groupby(['Continent_Name', 'date']).sum().reset_index()
 df['Total Deaths per Million'] = df.total_deaths * 1e6 / df.population
 df = df[df.date > '2020-03-14']
 df = df.rename({'date': 'Date', 'Continent_Name': 'Continent'}, axis='columns')
-px.line(df, x='Date', y='Total Deaths per Million', color='Continent').show()
+px.line(df, x='Date', y='Total Deaths per Million', color='Continent')
 ```
 
-#### Displays a multi-axis line chart of total coronavirus cases and changes in prices of Bitcoin, Dow Jones and gold:
+#### Displays a multi-axis line chart of total COVID-19 cases and changes in prices of Bitcoin, Dow Jones and gold:
 
 ![Covid Cases](web/covid_cases.png)
-<div id="e23ccacc-a456-478b-b467-7282a2165921" class="plotly-graph-div" style="height:287px; width:935px;"></div>
+<div id="e23ccacc-a456-478b-b467-7282a2165921" class="plotly-graph-div" style="height:285px; width:935px;"></div>
 
 ```python
-import pandas as pd, plotly.graph_objects as go
+# $ pip3 install pandas lxml selenium plotly
+import pandas as pd, selenium.webdriver, io, plotly.graph_objects as go
 
 def main():
-    covid, bitcoin, gold, dow = scrape_data()
+    covid, (bitcoin, gold, dow) = get_covid_cases(), get_tickers()
     df = wrangle_data(covid, bitcoin, gold, dow)
     display_data(df)
 
-def scrape_data():
-    def get_covid_cases():
-        url = 'https://covid.ourworldindata.org/data/owid-covid-data.csv'
-        df = pd.read_csv(url, usecols=['location', 'date', 'total_cases'])
-        df = df[df.location == 'World']
-        return df.set_index('date').total_cases
-    def get_ticker(symbol):
-        url = (f'https://query1.finance.yahoo.com/v7/finance/download/{symbol}?'
-               'period1=1579651200&period2=9999999999&interval=1d&events=history')
-        df = pd.read_csv(url, usecols=['Date', 'Close'])
-        return df.set_index('Date').Close
-    out = get_covid_cases(), get_ticker('BTC-USD'), get_ticker('GC=F'), get_ticker('^DJI')
-    names = ['Total Cases', 'Bitcoin', 'Gold', 'Dow Jones']
-    return map(pd.Series.rename, out, names)
+def get_covid_cases():
+    url = 'https://catalog.ourworldindata.org/garden/covid/latest/compact/compact.csv'
+    df = pd.read_csv(url, parse_dates=['date'])
+    df = df[df.country == 'World']
+    s = df.set_index('date').total_cases
+    return s.rename('Total Cases')
+
+def get_tickers():
+    with selenium.webdriver.Chrome() as driver:
+        driver.implicitly_wait(10)
+        symbols = {'Bitcoin': 'BTC-USD', 'Gold': 'GC=F', 'Dow Jones': '%5EDJI'}
+        return [get_ticker(driver, name, symbol) for name, symbol in symbols.items()]
+
+def get_ticker(driver, name, symbol):
+    url = f'https://finance.yahoo.com/quote/{symbol}/history/'
+    driver.get(url + '?period1=1579651200&period2=9999999999')
+    if buttons := driver.find_elements('xpath', '//button[@name="reject"]'):
+        buttons[0].click()
+    html = io.StringIO(driver.page_source)
+    dataframes = pd.read_html(html, parse_dates=['Date'])
+    s = dataframes[0].set_index('Date').Open
+    return s.rename(name)
 
 def wrangle_data(covid, bitcoin, gold, dow):
     df = pd.concat([bitcoin, gold, dow], axis=1)  # Creates table by joining columns on dates.
-    df = df.sort_index().interpolate()            # Sorts table by date and interpolates NaN-s.
-    df = df.loc['2020-02-23':]                    # Discards rows before '2020-02-23'.
+    df = df.sort_index().interpolate()            # Sorts rows by date and interpolates NaN-s.
+    df = df.loc['2020-02-23':'2021-12-20']        # Keeps rows between specified dates.
     df = (df / df.iloc[0]) * 100                  # Calculates percentages relative to day 1.
     df = df.join(covid)                           # Adds column with covid cases.
     return df.sort_values(df.index[-1], axis=1)   # Sorts columns by last day's value.
@@ -3491,14 +3487,15 @@ def display_data(df):
     figure = go.Figure()
     for col_name in reversed(df.columns):
         yaxis = 'y1' if col_name == 'Total Cases' else 'y2'
-        trace = go.Scatter(x=df.index, y=df[col_name], name=col_name, yaxis=yaxis)
+        trace = go.Scatter(x=df.index, y=df[col_name], yaxis=yaxis, name=col_name)
         figure.add_trace(trace)
     figure.update_layout(
+        width=944,
+        height=423,
         yaxis1=dict(title='Total Cases', rangemode='tozero'),
         yaxis2=dict(title='%', rangemode='tozero', overlaying='y', side='right'),
-        legend=dict(x=1.08),
-        width=944,
-        height=423
+        colorway=['#EF553B', '#636EFA', '#00CC96', '#FFA152'],
+        legend=dict(x=1.08)
     )
     figure.show()
 
@@ -3510,38 +3507,39 @@ if __name__ == '__main__':
 Appendix
 --------
 ### Cython
-**Library that compiles Python code into C.**
+**Library that compiles Python-like code into C.**
 
 ```python
 # $ pip3 install cython
-import pyximport; pyximport.install()
-import <cython_script>
-<cython_script>.main()
+import pyximport; pyximport.install()                # Module that runs Cython scripts.
+import <cython_script>                               # Script must have '.pyx' extension.
 ```
 
-#### Definitions:
-* **All `'cdef'` definitions are optional, but they contribute to the speed-up.**
-* **Script needs to be saved with a `'pyx'` extension.**
+#### All `'cdef'` definitions are optional, but they contribute to the speed-up:
+```python
+cdef <type> <var_name> [= <obj/var>]                 # Either Python or C type variable.
+cdef <ctype> *<pointer_name> [= &<var>]              # Use <pointer>[0] to get the value.
+cdef <ctype>[size] <array_name> [= <coll/array>]     # Also `<ctype>[:] <mview> = <array>`.
+cdef <ctype> *<array_name> [= <coll/array/pointer>]  # E.g. `<<ctype> *> malloc(n_bytes)`.
+```
 
 ```python
-cdef <ctype> <var_name> = <obj>
-cdef <ctype>[n_elements] <var_name> = [<el_1>, <el_2>, ...]
-cdef <ctype/void> <func_name>(<ctype> <arg_name>): ...
+cdef <type> <func_name>(<type> [*]<arg_name>): ...   # Omitted types default to `object`.
 ```
 
 ```python
-cdef class <class_name>:
-    cdef public <ctype> <attr_name>
-    def __init__(self, <ctype> <arg_name>):
-        self.<attr_name> = <arg_name>
+cdef class <class_name>:                             # Also `cdef struct <struct_name>:`.
+    cdef public <type> [*]<attr_name>                # Also `... <ctype> [*]<field_name>`.
+    def __init__(self, <type> <arg_name>):           # Also `cdef __dealloc__(self):`.
+        self.<attr_name> = <arg_name>                # Also `... free(<array/pointer>)`.
 ```
 
 ### Virtual Environments
 **System for installing libraries directly into project's directory.**
 
-```bash
+```perl
 $ python3 -m venv NAME      # Creates virtual environment in current directory.
-$ source NAME/bin/activate  # Activates env. On Windows run `NAME\Scripts\activate`.
+$ source NAME/bin/activate  # Activates it. On Windows run `NAME\Scripts\activate`.
 $ pip3 install LIBRARY      # Installs the library into active environment.
 $ python3 FILE              # Runs the script in active environment. Also `./FILE`.
 $ deactivate                # Deactivates the active virtual environment.
@@ -3582,7 +3580,6 @@ if __name__ == '__main__':
 
 Index
 -----
-* **Only available in the [PDF](https://transactions.sendowl.com/products/78175486/4422834F/view).**
 * **Ctrl+F / ⌘F is usually sufficient.**
 * **Searching `'#<title>'` on the [webpage](https://gto76.github.io/python-cheatsheet/) will limit the search to the titles.**
-* **Click on the `'🔗'` symbol to get a link to specific section.**
+* **Click on the title's `'🔗'` to get a link to its section.**
diff --git a/index.html b/index.html
index 53210903f..924e5366a 100644
--- a/index.html
+++ b/index.html
@@ -13,8 +13,9 @@
   <link rel="stylesheet" href="web/style.css">
 
   <script>
-    // Checks if URL ends with "index.html?dark=true"
-    if (window.location.search.search(/[?&]theme=dark3/) !== -1) {
+    // Uses dark theme 3 if it's specified in query string orbrowser prefers dark mode and 
+    // theme is not explicitly set.
+    if ((window.location.search.search(/[?&]theme=dark3/) !== -1) || ((window.location.search.search(/[?&]theme=/) == -1) && (window.matchMedia('(prefers-color-scheme: dark)').matches))) {
       document.write("<link rel=\"stylesheet\" href=\"web/default_dark3.min.css\">");
       document.write("<link rel=\"stylesheet\" href=\"web/style_dark3.css\">");
     }
@@ -55,25 +56,35 @@
 
 <body>
   <header>
-    <aside>November 7, 2024</aside>
+    <aside>July 31, 2025</aside>
     <a href="https://gto76.github.io" rel="author">Jure Šorn</a>
   </header>
 
-   <div><h1 id="comprehensivepythoncheatsheet">Comprehensive Python Cheatsheet</h1><p class="banner"><sup><a href="https://raw.githubusercontent.com/gto76/python-cheatsheet/main/README.md">Download text file</a>, <a href="https://transactions.sendowl.com/products/78175486/4422834F/view">Buy PDF</a>, <a href="https://github.com/gto76/python-cheatsheet">Fork me on GitHub</a>, <a href="https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions">Check out FAQ</a> or <a href="index.html?theme=dark3">Switch to dark theme</a>.
+   <div><h1 id="comprehensivepythoncheatsheet">Comprehensive Python Cheatsheet</h1><p class="banner"><sup><a href="https://raw.githubusercontent.com/gto76/python-cheatsheet/main/README.md">Download text file</a>, <a href="https://github.com/gto76/python-cheatsheet">Fork me on GitHub</a>, <a href="https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions">Check out FAQ</a> or <a href="index.html?theme=dark3">Switch to dark theme</a>.
 </sup></p><p class="banner" style="margin-bottom: 20px; padding-bottom: 7px;"><img src="web/image_888.jpeg" alt="Monty Python"></p><script>
-  // Changes the image and link to theme if URL ends with "index.html?theme=dark". 
-  if (window.location.search.search(/[?&]theme=dark/) !== -1) {
+  // Changes the banner image and link-to-theme if "theme=dark" is in query string
+  // or if browser prefers dark mode and theme is not explicitly set.
 
+const theme_not_set_in_query = window.location.search.search(/[?&]theme=light/) == -1
+const browser_prefers_dark = window.matchMedia('(prefers-color-scheme: dark)').matches;
+
+  if ((window.location.search.search(/[?&]theme=dark/) !== -1) || 
+      (theme_not_set_in_query && browser_prefers_dark)) {
+    activateDarkMode();
+  }
+
+  function activateDarkMode() {
     var link_to_theme = document.createElement("a")
-    link_to_theme.href = "index.html"
+    link_to_theme.href = "index.html?theme=light"
     link_to_theme.text = "Switch to light theme"
-    document.getElementsByClassName("banner")[0].firstChild.children[4].replaceWith(link_to_theme)
+    document.getElementsByClassName("banner")[0].firstChild.children[3].replaceWith(link_to_theme)
 
     var img_dark = document.createElement("img");
     img_dark.src = "web/image_orig_blue6.png";
     img_dark.alt = "Monthy Python";
     if ((window.location.search.search(/[?&]theme=dark2/) !== -1) ||
-        (window.location.search.search(/[?&]theme=dark3/) !== -1)) {
+        (window.location.search.search(/[?&]theme=dark3/) !== -1) ||
+        (theme_not_set_in_query && browser_prefers_dark)) {
       img_dark.style = "width: 910px;";
     } else {
       img_dark.style = "width: 960px;";
@@ -83,11 +94,11 @@
 </script><pre style="border-left: none;padding-left: 1.9px;"><code class="hljs bash" style="line-height: 1.327em;"><strong>ToC</strong> = {
     <strong><span class="hljs-string"><span class="hljs-string">'1. Collections'</span></span></strong>: [<a href="#list">List</a>, <a href="#dictionary">Dictionary</a>, <a href="#set">Set</a>, <a href="#tuple">Tuple</a>, <a href="#range">Range</a>, <a href="#enumerate">Enumerate</a>, <a href="#iterator">Iterator</a>, <a href="#generator">Generator</a>],
     <strong><span class="hljs-string"><span class="hljs-string">'2. Types'</span></span></strong>:       [<a href="#type">Type</a>, <a href="#string">String</a>, <a href="#regex">Regular_Exp</a>, <a href="#format">Format</a>, <a href="#numbers">Numbers</a>, <a href="#combinatorics">Combinatorics</a>, <a href="#datetime">Datetime</a>],
-    <strong><span class="hljs-string"><span class="hljs-string">'3. Syntax'</span></span></strong>:      [<a href="#arguments">Args</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#ducktypes">Duck_Types</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Exception</a>],
+    <strong><span class="hljs-string"><span class="hljs-string">'3. Syntax'</span></span></strong>:      [<a href="#function">Function</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#ducktypes">Duck_Type</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Except</a>],
     <strong><span class="hljs-string"><span class="hljs-string">'4. System'</span></span></strong>:      [<a href="#exit">Exit</a>, <a href="#print">Print</a>, <a href="#input">Input</a>, <a href="#commandlinearguments">Command_Line_Arguments</a>, <a href="#open">Open</a>, <a href="#paths">Path</a>, <a href="#oscommands">OS_Commands</a>],
     <strong><span class="hljs-string"><span class="hljs-string">'5. Data'</span></span></strong>:        [<a href="#json">JSON</a>, <a href="#pickle">Pickle</a>, <a href="#csv">CSV</a>, <a href="#sqlite">SQLite</a>, <a href="#bytes">Bytes</a>, <a href="#struct">Struct</a>, <a href="#array">Array</a>, <a href="#memoryview">Memory_View</a>, <a href="#deque">Deque</a>],
-    <strong><span class="hljs-string"><span class="hljs-string">'6. Advanced'</span></span></strong>:    [<a href="#threading">Threading</a>, <a href="#operator">Operator</a>, <a href="#matchstatement">Match_Stmt</a>, <a href="#logging">Logging</a>, <a href="#introspection">Introspection</a>, <a href="#coroutines">Coroutines</a>],
-    <strong><span class="hljs-string"><span class="hljs-string">'7. Libraries'</span></span></strong>:   [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#consoleapp">Console_App</a>, <a href="#guiapp">GUI</a>, <a href="#scraping">Scraping</a>, <a href="#web">Web</a>, <a href="#profiling">Profile</a>],
+    <strong><span class="hljs-string"><span class="hljs-string">'6. Advanced'</span></span></strong>:    [<a href="#operator">Operator</a>, <a href="#matchstatement">Match_Stmt</a>, <a href="#logging">Logging</a>, <a href="#introspection">Introspection</a>, <a href="#threading">Threading</a>, <a href="#coroutines">Coroutines</a>],
+    <strong><span class="hljs-string"><span class="hljs-string">'7. Libraries'</span></span></strong>:   [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#consoleapp">Console_App</a>, <a href="#guiapp">GUI</a>, <a href="#scraping">Scraping</a>, <a href="#webapp">Web</a>, <a href="#profiling">Profile</a>],
     <strong><span class="hljs-string"><span class="hljs-string">'8. Multimedia'</span></span></strong>:  [<a href="#numpy">NumPy</a>, <a href="#image">Image</a>, <a href="#animation">Animation</a>, <a href="#audio">Audio</a>, <a href="#synthesizer">Synthesizer</a>, <a href="#pygame">Pygame</a>, <a href="#pandas">Pandas</a>, <a href="#plotly">Plotly</a>]
 }
 </code></pre></div>
@@ -100,7 +111,7 @@
     main()                      <span class="hljs-comment"># Runs `def main(): ...` function.</span>
 </code></pre></div>
 
-<div><h2 id="list"><a href="#list" name="list">#</a>List</h2><pre><code class="python language-python hljs">&lt;list&gt; = [&lt;el_1&gt;, &lt;el_2&gt;, ...]  <span class="hljs-comment"># Creates new list. Also list(&lt;collection&gt;).</span>
+<div><h2 id="list"><a href="#list" name="list">#</a>List</h2><pre><code class="python language-python hljs">&lt;list&gt; = [&lt;el_1&gt;, &lt;el_2&gt;, ...]  <span class="hljs-comment"># Creates a list object. Also list(&lt;collection&gt;).</span>
 </code></pre></div>
 
 <pre><code class="python language-python hljs">&lt;el&gt;   = &lt;list&gt;[index]          <span class="hljs-comment"># First index is 0. Last -1. Allows assignments.</span>
@@ -109,39 +120,40 @@
 <pre><code class="python language-python hljs">&lt;list&gt;.append(&lt;el&gt;)             <span class="hljs-comment"># Appends element to the end. Also &lt;list&gt; += [&lt;el&gt;].</span>
 &lt;list&gt;.extend(&lt;collection&gt;)     <span class="hljs-comment"># Appends elements to the end. Also &lt;list&gt; += &lt;coll&gt;.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;list&gt;.sort()                   <span class="hljs-comment"># Sorts elements in ascending order.</span>
-&lt;list&gt;.reverse()                <span class="hljs-comment"># Reverses the list in-place.</span>
-&lt;list&gt; = sorted(&lt;collection&gt;)   <span class="hljs-comment"># Returns new list with sorted elements.</span>
+<pre><code class="python language-python hljs">&lt;list&gt;.sort()                   <span class="hljs-comment"># Sorts the elements in ascending order.</span>
+&lt;list&gt;.reverse()                <span class="hljs-comment"># Reverses the order of list's elements.</span>
+&lt;list&gt; = sorted(&lt;collection&gt;)   <span class="hljs-comment"># Returns a new list with sorted elements.</span>
 &lt;iter&gt; = reversed(&lt;list&gt;)       <span class="hljs-comment"># Returns reversed iterator of elements.</span>
 </code></pre>
-<pre><code class="python language-python hljs">sum_of_elements  = sum(&lt;collection&gt;)
-elementwise_sum  = [sum(pair) <span class="hljs-keyword">for</span> pair <span class="hljs-keyword">in</span> zip(list_a, list_b)]
+<pre><code class="python language-python hljs">&lt;el&gt;  = max(&lt;collection&gt;)       <span class="hljs-comment"># Returns largest element. Also min(&lt;el_1&gt;, ...).</span>
+&lt;num&gt; = sum(&lt;collection&gt;)       <span class="hljs-comment"># Returns sum of elements. Also math.prod(&lt;coll&gt;).</span>
+</code></pre>
+<pre><code class="python language-python hljs">elementwise_sum  = [sum(pair) <span class="hljs-keyword">for</span> pair <span class="hljs-keyword">in</span> zip(list_a, list_b)]
 sorted_by_second = sorted(&lt;collection&gt;, key=<span class="hljs-keyword">lambda</span> el: el[<span class="hljs-number">1</span>])
 sorted_by_both   = sorted(&lt;collection&gt;, key=<span class="hljs-keyword">lambda</span> el: (el[<span class="hljs-number">1</span>], el[<span class="hljs-number">0</span>]))
 flatter_list     = list(itertools.chain.from_iterable(&lt;list&gt;))
-product_of_elems = functools.reduce(<span class="hljs-keyword">lambda</span> out, el: out * el, &lt;collection&gt;)
-list_of_chars    = list(&lt;str&gt;)
 </code></pre>
 <ul>
-<li><strong>For details about sorted(), min() and max() see <a href="#sortable">sortable</a>.</strong></li>
-<li><strong>Module <a href="#operator">operator</a> provides functions itemgetter() and mul() that offer the same functionality as <a href="#lambda">lambda</a> expressions above.</strong></li>
+<li><strong>For details about sort(), sorted(), min() and max() see <a href="#sortable">Sortable</a>.</strong></li>
+<li><strong>Module <a href="#operator">operator</a> has function itemgetter() that can replace listed <a href="#lambda">lambdas</a>.</strong></li>
+<li><strong>This text uses the term collection instead of iterable. For rationale see <a href="#collection">Collection</a>.</strong></li>
 </ul>
-<pre><code class="python language-python hljs">&lt;int&gt; = len(&lt;list&gt;)             <span class="hljs-comment"># Returns number of items. Also works on other collections.</span>
+<pre><code class="python language-python hljs">&lt;int&gt; = len(&lt;list&gt;)             <span class="hljs-comment"># Returns number of items. Also works on dict, set and string.</span>
 &lt;int&gt; = &lt;list&gt;.count(&lt;el&gt;)      <span class="hljs-comment"># Returns number of occurrences. Also `if &lt;el&gt; in &lt;coll&gt;: ...`.</span>
 &lt;int&gt; = &lt;list&gt;.index(&lt;el&gt;)      <span class="hljs-comment"># Returns index of the first occurrence or raises ValueError.</span>
 &lt;el&gt;  = &lt;list&gt;.pop()            <span class="hljs-comment"># Removes and returns item from the end or at index if passed.</span>
-&lt;list&gt;.insert(&lt;int&gt;, &lt;el&gt;)      <span class="hljs-comment"># Inserts item at index and moves the rest to the right.</span>
+&lt;list&gt;.insert(&lt;int&gt;, &lt;el&gt;)      <span class="hljs-comment"># Inserts item at passed index and moves the rest to the right.</span>
 &lt;list&gt;.remove(&lt;el&gt;)             <span class="hljs-comment"># Removes first occurrence of the item or raises ValueError.</span>
-&lt;list&gt;.clear()                  <span class="hljs-comment"># Removes all items. Also works on dictionary and set.</span>
+&lt;list&gt;.clear()                  <span class="hljs-comment"># Removes all list's items. Also works on dictionary and set.</span>
 </code></pre>
 <div><h2 id="dictionary"><a href="#dictionary" name="dictionary">#</a>Dictionary</h2><pre><code class="python language-python hljs">&lt;dict&gt; = {key_1: val_1, key_2: val_2, ...}      <span class="hljs-comment"># Use `&lt;dict&gt;[key]` to get or set the value.</span>
 </code></pre></div>
 
-<pre><code class="python language-python hljs">&lt;view&gt; = &lt;dict&gt;.keys()                          <span class="hljs-comment"># Coll. of keys that reflects changes.</span>
-&lt;view&gt; = &lt;dict&gt;.values()                        <span class="hljs-comment"># Coll. of values that reflects changes.</span>
+<pre><code class="python language-python hljs">&lt;view&gt; = &lt;dict&gt;.keys()                          <span class="hljs-comment"># Collection of keys that reflects changes.</span>
+&lt;view&gt; = &lt;dict&gt;.values()                        <span class="hljs-comment"># Collection of values that reflects changes.</span>
 &lt;view&gt; = &lt;dict&gt;.items()                         <span class="hljs-comment"># Coll. of key-value tuples that reflects chgs.</span>
 </code></pre>
-<pre><code class="python language-python hljs">value  = &lt;dict&gt;.get(key, default=<span class="hljs-keyword">None</span>)          <span class="hljs-comment"># Returns default if key is missing.</span>
+<pre><code class="python language-python hljs">value  = &lt;dict&gt;.get(key, default=<span class="hljs-keyword">None</span>)          <span class="hljs-comment"># Returns default argument if key is missing.</span>
 value  = &lt;dict&gt;.setdefault(key, default=<span class="hljs-keyword">None</span>)   <span class="hljs-comment"># Returns and writes default if key is missing.</span>
 &lt;dict&gt; = collections.defaultdict(&lt;type&gt;)        <span class="hljs-comment"># Returns a dict with default value `&lt;type&gt;()`.</span>
 &lt;dict&gt; = collections.defaultdict(<span class="hljs-keyword">lambda</span>: <span class="hljs-number">1</span>)     <span class="hljs-comment"># Returns a dict with default value 1.</span>
@@ -153,7 +165,7 @@
 <pre><code class="python language-python hljs">&lt;dict&gt;.update(&lt;dict&gt;)                           <span class="hljs-comment"># Adds items. Replaces ones with matching keys.</span>
 value = &lt;dict&gt;.pop(key)                         <span class="hljs-comment"># Removes item or raises KeyError if missing.</span>
 {k <span class="hljs-keyword">for</span> k, v <span class="hljs-keyword">in</span> &lt;dict&gt;.items() <span class="hljs-keyword">if</span> v == value}    <span class="hljs-comment"># Returns set of keys that point to the value.</span>
-{k: v <span class="hljs-keyword">for</span> k, v <span class="hljs-keyword">in</span> &lt;dict&gt;.items() <span class="hljs-keyword">if</span> k <span class="hljs-keyword">in</span> keys}  <span class="hljs-comment"># Filters the dictionary by keys.</span>
+{k: v <span class="hljs-keyword">for</span> k, v <span class="hljs-keyword">in</span> &lt;dict&gt;.items() <span class="hljs-keyword">if</span> k <span class="hljs-keyword">in</span> keys}  <span class="hljs-comment"># Filters the dictionary by specified keys.</span>
 </code></pre>
 <div><h3 id="counter">Counter</h3><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> Counter
 <span class="hljs-meta">&gt;&gt;&gt; </span>counter = Counter([<span class="hljs-string">'blue'</span>, <span class="hljs-string">'blue'</span>, <span class="hljs-string">'blue'</span>, <span class="hljs-string">'red'</span>, <span class="hljs-string">'red'</span>])
@@ -194,20 +206,17 @@
 
 <div><h3 id="namedtuple">Named Tuple</h3><p><strong>Tuple's subclass with named elements.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
 <span class="hljs-meta">&gt;&gt;&gt; </span>Point = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>)
-<span class="hljs-meta">&gt;&gt;&gt; </span>p = Point(<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>); p
+<span class="hljs-meta">&gt;&gt;&gt; </span>p = Point(<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>)
+<span class="hljs-meta">&gt;&gt;&gt; </span>print(p)
 Point(x=<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>)
-<span class="hljs-meta">&gt;&gt;&gt; </span>p[<span class="hljs-number">0</span>]
-<span class="hljs-number">1</span>
-<span class="hljs-meta">&gt;&gt;&gt; </span>p.x
-<span class="hljs-number">1</span>
-<span class="hljs-meta">&gt;&gt;&gt; </span>getattr(p, <span class="hljs-string">'y'</span>)
-<span class="hljs-number">2</span>
+<span class="hljs-meta">&gt;&gt;&gt; </span>p.x, p[<span class="hljs-number">1</span>]
+(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>)
 </code></pre></div>
 
 
-<div><h2 id="range"><a href="#range" name="range">#</a>Range</h2><p><strong>Immutable and hashable sequence of integers.</strong></p><pre><code class="python language-python hljs">&lt;range&gt; = range(stop)                      <span class="hljs-comment"># range(to_exclusive)</span>
-&lt;range&gt; = range(start, stop)               <span class="hljs-comment"># range(from_inclusive, to_exclusive)</span>
-&lt;range&gt; = range(start, stop, ±step)        <span class="hljs-comment"># range(from_inclusive, to_exclusive, ±step_size)</span>
+<div><h2 id="range"><a href="#range" name="range">#</a>Range</h2><p><strong>Immutable and hashable sequence of integers.</strong></p><pre><code class="python language-python hljs">&lt;range&gt; = range(stop)                      <span class="hljs-comment"># I.e. range(to_exclusive).</span>
+&lt;range&gt; = range(start, stop)               <span class="hljs-comment"># I.e. range(from_inclusive, to_exclusive).</span>
+&lt;range&gt; = range(start, stop, ±step)        <span class="hljs-comment"># I.e. range(from_inclusive, to_exclusive, ±step).</span>
 </code></pre></div>
 
 
@@ -218,20 +227,21 @@
     ...
 </code></pre></div>
 
-<div><h2 id="iterator"><a href="#iterator" name="iterator">#</a>Iterator</h2><pre><code class="python language-python hljs">&lt;iter&gt; = iter(&lt;collection&gt;)                <span class="hljs-comment"># `iter(&lt;iter&gt;)` returns unmodified iterator.</span>
+<div><h2 id="iterator"><a href="#iterator" name="iterator">#</a>Iterator</h2><p><strong>Potentially endless stream of elements.</strong></p><pre><code class="python language-python hljs">&lt;iter&gt; = iter(&lt;collection&gt;)                <span class="hljs-comment"># `iter(&lt;iter&gt;)` returns unmodified iterator.</span>
 &lt;iter&gt; = iter(&lt;function&gt;, to_exclusive)    <span class="hljs-comment"># A sequence of return values until 'to_exclusive'.</span>
 &lt;el&gt;   = next(&lt;iter&gt; [, default])          <span class="hljs-comment"># Raises StopIteration or returns 'default' on end.</span>
 &lt;list&gt; = list(&lt;iter&gt;)                      <span class="hljs-comment"># Returns a list of iterator's remaining elements.</span>
 </code></pre></div>
 
+
 <div><h3 id="itertools">Itertools</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> itertools <span class="hljs-keyword">as</span> it
 </code></pre></div>
 
 <pre><code class="python language-python hljs">&lt;iter&gt; = it.count(start=<span class="hljs-number">0</span>, step=<span class="hljs-number">1</span>)         <span class="hljs-comment"># Returns updated value endlessly. Accepts floats.</span>
 &lt;iter&gt; = it.repeat(&lt;el&gt; [, times])         <span class="hljs-comment"># Returns element endlessly or 'times' times.</span>
-&lt;iter&gt; = it.cycle(&lt;collection&gt;)            <span class="hljs-comment"># Repeats the sequence endlessly.</span>
+&lt;iter&gt; = it.cycle(&lt;collection&gt;)            <span class="hljs-comment"># Repeats the passed sequence of elements endlessly.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;iter&gt; = it.chain(&lt;coll&gt;, &lt;coll&gt; [, ...])  <span class="hljs-comment"># Empties collections in order (figuratively).</span>
+<pre><code class="python language-python hljs">&lt;iter&gt; = it.chain(&lt;coll&gt;, &lt;coll&gt; [, ...])  <span class="hljs-comment"># Empties collections in order (only figuratively).</span>
 &lt;iter&gt; = it.chain.from_iterable(&lt;coll&gt;)    <span class="hljs-comment"># Empties collections inside a collection in order.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;iter&gt; = it.islice(&lt;coll&gt;, to_exclusive)   <span class="hljs-comment"># Only returns first 'to_exclusive' elements.</span>
@@ -300,21 +310,21 @@
 
 
 <pre><code class="python language-python hljs">&lt;list&gt; = &lt;str&gt;.split()                       <span class="hljs-comment"># Splits on one or more whitespace characters.</span>
-&lt;list&gt; = &lt;str&gt;.split(sep=<span class="hljs-keyword">None</span>, maxsplit=<span class="hljs-number">-1</span>)  <span class="hljs-comment"># Splits on 'sep' str at most 'maxsplit' times.</span>
+&lt;list&gt; = &lt;str&gt;.split(sep=<span class="hljs-keyword">None</span>, maxsplit=<span class="hljs-number">-1</span>)  <span class="hljs-comment"># Splits on 'sep' string at most 'maxsplit' times.</span>
 &lt;list&gt; = &lt;str&gt;.splitlines(keepends=<span class="hljs-keyword">False</span>)    <span class="hljs-comment"># On [\n\r\f\v\x1c-\x1e\x85\u2028\u2029] and \r\n.</span>
-&lt;str&gt;  = &lt;str&gt;.join(&lt;coll_of_strings&gt;)       <span class="hljs-comment"># Joins elements using string as a separator.</span>
+&lt;str&gt;  = &lt;str&gt;.join(&lt;coll_of_strings&gt;)       <span class="hljs-comment"># Joins elements by using string as a separator.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;bool&gt; = &lt;sub_str&gt; <span class="hljs-keyword">in</span> &lt;str&gt;                  <span class="hljs-comment"># Checks if string contains the substring.</span>
 &lt;bool&gt; = &lt;str&gt;.startswith(&lt;sub_str&gt;)         <span class="hljs-comment"># Pass tuple of strings for multiple options.</span>
 &lt;int&gt;  = &lt;str&gt;.find(&lt;sub_str&gt;)               <span class="hljs-comment"># Returns start index of the first match or -1.</span>
-&lt;int&gt;  = &lt;str&gt;.index(&lt;sub_str&gt;)              <span class="hljs-comment"># Same, but raises ValueError if there's no match.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;str&gt;  = &lt;str&gt;.lower()                       <span class="hljs-comment"># Changes the case. Also upper/capitalize/title().</span>
+<pre><code class="python language-python hljs">&lt;str&gt;  = &lt;str&gt;.lower()                       <span class="hljs-comment"># Lowers the case. Also upper/capitalize/title().</span>
+&lt;str&gt;  = &lt;str&gt;.casefold()                    <span class="hljs-comment"># Same, but converts ẞ/ß to ss, Σ/ς to σ, etc.</span>
 &lt;str&gt;  = &lt;str&gt;.replace(old, new [, count])   <span class="hljs-comment"># Replaces 'old' with 'new' at most 'count' times.</span>
 &lt;str&gt;  = &lt;str&gt;.translate(&lt;table&gt;)            <span class="hljs-comment"># Use `str.maketrans(&lt;dict&gt;)` to generate table.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;str&gt;  = chr(&lt;int&gt;)                          <span class="hljs-comment"># Converts int to Unicode character.</span>
-&lt;int&gt;  = ord(&lt;str&gt;)                          <span class="hljs-comment"># Converts Unicode character to int.</span>
+<pre><code class="python language-python hljs">&lt;str&gt;  = chr(&lt;int&gt;)                          <span class="hljs-comment"># Converts passed integer to Unicode character.</span>
+&lt;int&gt;  = ord(&lt;str&gt;)                          <span class="hljs-comment"># Converts passed Unicode character to integer.</span>
 </code></pre>
 <ul>
 <li><strong>Use <code class="python hljs"><span class="hljs-string">'unicodedata.normalize("NFC", &lt;str&gt;)'</span></code> on strings like <code class="python hljs"><span class="hljs-string">'Motörhead'</span></code> before comparing them to other strings, because <code class="python hljs"><span class="hljs-string">'ö'</span></code> can be stored as one or two characters.</strong></li>
@@ -325,12 +335,12 @@
 &lt;bool&gt; = &lt;str&gt;.isnumeric()                   <span class="hljs-comment"># Checks for [¼½¾…], [零〇一…] and isdigit().</span>
 &lt;bool&gt; = &lt;str&gt;.isalnum()                     <span class="hljs-comment"># Checks for [a-zA-Z…] and isnumeric().</span>
 &lt;bool&gt; = &lt;str&gt;.isprintable()                 <span class="hljs-comment"># Checks for [ !#$%…] and isalnum().</span>
-&lt;bool&gt; = &lt;str&gt;.isspace()                     <span class="hljs-comment"># Checks for [ \t\n\r\f\v\x1c-\x1f\x85\xa0…].</span>
+&lt;bool&gt; = &lt;str&gt;.isspace()                     <span class="hljs-comment"># Checks for [ \t\n\r\f\v\x1c-\x1f\x85…].</span>
 </code></pre></div>
 
 <div><h2 id="regex"><a href="#regex" name="regex">#</a>Regex</h2><p><strong>Functions for regular expression matching.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> re
 &lt;str&gt;   = re.sub(<span class="hljs-string">r'&lt;regex&gt;'</span>, new, text, count=<span class="hljs-number">0</span>)  <span class="hljs-comment"># Substitutes all occurrences with 'new'.</span>
-&lt;list&gt;  = re.findall(<span class="hljs-string">r'&lt;regex&gt;'</span>, text)            <span class="hljs-comment"># Returns all occurrences as strings.</span>
+&lt;list&gt;  = re.findall(<span class="hljs-string">r'&lt;regex&gt;'</span>, text)            <span class="hljs-comment"># Returns all occurrences of the pattern.</span>
 &lt;list&gt;  = re.split(<span class="hljs-string">r'&lt;regex&gt;'</span>, text, maxsplit=<span class="hljs-number">0</span>)  <span class="hljs-comment"># Add brackets around regex to keep matches.</span>
 &lt;Match&gt; = re.search(<span class="hljs-string">r'&lt;regex&gt;'</span>, text)             <span class="hljs-comment"># First occurrence of the pattern or None.</span>
 &lt;Match&gt; = re.match(<span class="hljs-string">r'&lt;regex&gt;'</span>, text)              <span class="hljs-comment"># Searches only at the beginning of the text.</span>
@@ -341,16 +351,16 @@
 <ul>
 <li><strong>Raw string literals do not interpret escape sequences, thus enabling us to use regex-specific escape sequences that cause SyntaxWarning in normal string literals (since 3.12).</strong></li>
 <li><strong>Argument 'new' of re.sub() can be a function that accepts Match object and returns a str.</strong></li>
-<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.IGNORECASE'</span></code> can be used with all functions.</strong></li>
+<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.IGNORECASE'</span></code> can be used with all functions that are listed above.</strong></li>
 <li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.MULTILINE'</span></code> makes <code class="python hljs"><span class="hljs-string">'^'</span></code> and <code class="python hljs"><span class="hljs-string">'$'</span></code> match the start/end of each line.</strong></li>
-<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.DOTALL'</span></code> makes <code class="python hljs"><span class="hljs-string">'.'</span></code> also accept the <code class="python hljs"><span class="hljs-string">'\n'</span></code>.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'re.compile(&lt;regex&gt;)'</span></code> returns a Pattern object with methods sub(), findall(), …</strong></li>
+<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.DOTALL'</span></code> makes <code class="python hljs"><span class="hljs-string">'.'</span></code> also accept the <code class="python hljs"><span class="hljs-string">'\n'</span></code> (besides all other chars).</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'re.compile(&lt;regex&gt;)'</span></code> returns a Pattern object with methods sub(), findall(), etc.</strong></li>
 </ul>
 <div><h3 id="matchobject">Match Object</h3><pre><code class="python language-python hljs">&lt;str&gt;   = &lt;Match&gt;.group()                         <span class="hljs-comment"># Returns the whole match. Also group(0).</span>
 &lt;str&gt;   = &lt;Match&gt;.group(<span class="hljs-number">1</span>)                        <span class="hljs-comment"># Returns part inside the first brackets.</span>
-&lt;tuple&gt; = &lt;Match&gt;.groups()                        <span class="hljs-comment"># Returns all bracketed parts.</span>
-&lt;int&gt;   = &lt;Match&gt;.start()                         <span class="hljs-comment"># Returns start index of the match.</span>
-&lt;int&gt;   = &lt;Match&gt;.end()                           <span class="hljs-comment"># Returns exclusive end index of the match.</span>
+&lt;tuple&gt; = &lt;Match&gt;.groups()                        <span class="hljs-comment"># Returns all bracketed parts as strings.</span>
+&lt;int&gt;   = &lt;Match&gt;.start()                         <span class="hljs-comment"># Returns start index of the whole match.</span>
+&lt;int&gt;   = &lt;Match&gt;.end()                           <span class="hljs-comment"># Returns its exclusive end index.</span>
 </code></pre></div>
 
 <div><h3 id="specialsequences">Special Sequences</h3><pre><code class="python language-python hljs"><span class="hljs-string">'\d'</span> == <span class="hljs-string">'[0-9]'</span>                                   <span class="hljs-comment"># Also [०-९…]. Matches a decimal character.</span>
@@ -359,12 +369,11 @@
 </code></pre></div>
 
 <ul>
-<li><strong>By default, decimal characters, alphanumerics and whitespaces from all alphabets are matched unless <code class="python hljs"><span class="hljs-string">'flags=re.ASCII'</span></code> argument is used.</strong></li>
-<li><strong>It restricts special sequence matches to <code class="python hljs"><span class="hljs-string">'[\x00-\x7f]'</span></code> (the first 128 characters) and also prevents <code class="python hljs"><span class="hljs-string">'\s'</span></code> from accepting <code class="python hljs"><span class="hljs-string">'[\x1c-\x1f]'</span></code> (file, table, row, and field separators).</strong></li>
+<li><strong>By default, decimal characters and alphanumerics from all alphabets are matched unless <code class="python hljs"><span class="hljs-string">'flags=re.ASCII'</span></code> is used. It restricts special sequence matches to the first 128 Unicode characters and also prevents <code class="python hljs"><span class="hljs-string">'\s'</span></code> from accepting <code class="python hljs"><span class="hljs-string">'\x1c'</span></code>, <code class="python hljs"><span class="hljs-string">'\x1d'</span></code>, <code class="python hljs"><span class="hljs-string">'\x1e'</span></code> and <code class="python hljs"><span class="hljs-string">'\x1f'</span></code> (non-printable characters that divide text into files, tables, rows and fields, respectively).</strong></li>
 <li><strong>Use a capital letter for negation (all non-ASCII characters will be matched when used in combination with ASCII flag).</strong></li>
 </ul>
-<div><h2 id="format"><a href="#format" name="format">#</a>Format</h2><pre><code class="python hljs">&lt;str&gt; = <span class="hljs-string">f'<span class="hljs-subst">{&lt;el_1&gt;}</span>, <span class="hljs-subst">{&lt;el_2&gt;}</span>'</span>            <span class="hljs-comment"># Curly brackets can also contain expressions.</span>
-&lt;str&gt; = <span class="hljs-string">'{}, {}'</span>.format(&lt;el_1&gt;, &lt;el_2&gt;)  <span class="hljs-comment"># Or: '{0}, {a}'.format(&lt;el_1&gt;, a=&lt;el_2&gt;)</span>
+<div><h2 id="format"><a href="#format" name="format">#</a>Format</h2><pre><code class="python hljs">&lt;str&gt; = <span class="hljs-string">f'<span class="hljs-subst">{&lt;el_1&gt;}</span>, <span class="hljs-subst">{&lt;el_2&gt;}</span>'</span>            <span class="hljs-comment"># Curly braces can also contain expressions.</span>
+&lt;str&gt; = <span class="hljs-string">'{}, {}'</span>.format(&lt;el_1&gt;, &lt;el_2&gt;)  <span class="hljs-comment"># Same as '{0}, {a}'.format(&lt;el_1&gt;, a=&lt;el_2&gt;).</span>
 &lt;str&gt; = <span class="hljs-string">'%s, %s'</span> % (&lt;el_1&gt;, &lt;el_2&gt;)      <span class="hljs-comment"># Redundant and inferior C-style formatting.</span>
 </code></pre></div>
 
@@ -382,8 +391,8 @@
 </code></pre></div>
 
 <ul>
-<li><strong>Objects are rendered using <code class="python hljs"><span class="hljs-string">'format(&lt;el&gt;, "&lt;options&gt;")'</span></code>.</strong></li>
-<li><strong>Options can be generated dynamically: <code class="python hljs"><span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;:{&lt;str/int&gt;}</span>[…]}'</span></code>.</strong></li>
+<li><strong>Objects are rendered by calling the <code class="python hljs"><span class="hljs-string">'format(&lt;el&gt;, "&lt;options&gt;")'</span></code> function.</strong></li>
+<li><strong>Options inside curly braces can be generated dynamically: <code class="python hljs"><span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;:{&lt;str/int&gt;}</span>[…]}'</span></code>.</strong></li>
 <li><strong>Adding <code class="python hljs"><span class="hljs-string">'='</span></code> to the expression prepends it to the output: <code class="python hljs"><span class="hljs-string">f'<span class="hljs-subst">{<span class="hljs-number">1</span>+<span class="hljs-number">1</span>=}</span>'</span></code> returns <code class="python hljs"><span class="hljs-string">'1+1=2'</span></code>.</strong></li>
 <li><strong>Adding <code class="python hljs"><span class="hljs-string">'!r'</span></code> to the expression converts object to string by calling its <a href="#class">repr()</a> method.</strong></li>
 </ul>
@@ -440,80 +449,80 @@
 <li><strong>This rule only effects numbers that can be represented exactly by a float (<code class="python hljs"><span class="hljs-number">.5</span></code>, <code class="python hljs"><span class="hljs-number">.25</span></code>, …).</strong></li>
 </ul>
 <div><h3 id="ints">Ints</h3><pre><code class="python language-python hljs">{<span class="hljs-number">90</span>:c}                                   <span class="hljs-comment"># 'Z'. Unicode character with value 90.</span>
-{<span class="hljs-number">90</span>:b}                                   <span class="hljs-comment"># '1011010'. Number 90 in binary.</span>
-{<span class="hljs-number">90</span>:X}                                   <span class="hljs-comment"># '5A'. Number 90 in uppercase hexadecimal.</span>
+{<span class="hljs-number">90</span>:b}                                   <span class="hljs-comment"># '1011010'. Binary representation of the int.</span>
+{<span class="hljs-number">90</span>:X}                                   <span class="hljs-comment"># '5A'. Hexadecimal with upper-case letters.</span>
 </code></pre></div>
 
-<div><h2 id="numbers"><a href="#numbers" name="numbers">#</a>Numbers</h2><pre><code class="python language-python hljs">&lt;int&gt;      = int(&lt;float/str/bool&gt;)                <span class="hljs-comment"># Or: math.floor(&lt;float&gt;)</span>
-&lt;float&gt;    = float(&lt;int/str/bool&gt;)                <span class="hljs-comment"># Or: &lt;int/float&gt;e±&lt;int&gt;</span>
-&lt;complex&gt;  = complex(real=<span class="hljs-number">0</span>, imag=<span class="hljs-number">0</span>)              <span class="hljs-comment"># Or: &lt;int/float&gt; ± &lt;int/float&gt;j</span>
-&lt;Fraction&gt; = fractions.Fraction(<span class="hljs-number">0</span>, <span class="hljs-number">1</span>)             <span class="hljs-comment"># Or: Fraction(numerator=0, denominator=1)</span>
-&lt;Decimal&gt;  = decimal.Decimal(&lt;str/int&gt;)           <span class="hljs-comment"># Or: Decimal((sign, digits, exponent))</span>
+<div><h2 id="numbers"><a href="#numbers" name="numbers">#</a>Numbers</h2><pre><code class="python language-python hljs">&lt;int&gt;      = int(&lt;float/str/bool&gt;)             <span class="hljs-comment"># Whole number of any size. Truncates floats.</span>
+&lt;float&gt;    = float(&lt;int/str/bool&gt;)             <span class="hljs-comment"># 64-bit decimal number. Also &lt;float&gt;e±&lt;int&gt;.</span>
+&lt;complex&gt;  = complex(real=<span class="hljs-number">0</span>, imag=<span class="hljs-number">0</span>)           <span class="hljs-comment"># A complex number. Also `&lt;float&gt; ± &lt;float&gt;j`.</span>
+&lt;Fraction&gt; = fractions.Fraction(&lt;int&gt;, &lt;int&gt;)  <span class="hljs-comment"># E.g. `Fraction(1, 2) / 3 == Fraction(1, 6)`.</span>
+&lt;Decimal&gt;  = decimal.Decimal(&lt;str/int/tuple&gt;)  <span class="hljs-comment"># E.g. `Decimal((1, (2, 3), 4)) == -230_000`.</span>
 </code></pre></div>
 
 <ul>
-<li><strong><code class="python hljs"><span class="hljs-string">'int(&lt;str&gt;)'</span></code> and <code class="python hljs"><span class="hljs-string">'float(&lt;str&gt;)'</span></code> raise ValueError on malformed strings.</strong></li>
-<li><strong>Decimal numbers are stored exactly, unlike most floats where <code class="python hljs"><span class="hljs-string">'1.1 + 2.2 != 3.3'</span></code>.</strong></li>
-<li><strong>Floats can be compared with: <code class="python hljs"><span class="hljs-string">'math.isclose(&lt;float&gt;, &lt;float&gt;)'</span></code>.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'int(&lt;str&gt;)'</span></code> and <code class="python hljs"><span class="hljs-string">'float(&lt;str&gt;)'</span></code> raise ValueError if passed string is malformed.</strong></li>
+<li><strong>Decimal objects store numbers exactly, unlike most floats where <code class="python hljs"><span class="hljs-string">'1.1 + 2.2 != 3.3'</span></code>.</strong></li>
+<li><strong>Floats can be compared with: <code class="python hljs"><span class="hljs-string">'math.isclose(&lt;float&gt;, &lt;float&gt;, rel_tol=1e-09)'</span></code>.</strong></li>
 <li><strong>Precision of decimal operations is set with: <code class="python hljs"><span class="hljs-string">'decimal.getcontext().prec = &lt;int&gt;'</span></code>.</strong></li>
+<li><strong>Bools can be used anywhere ints can, because bool is a subclass of int: <code class="python hljs"><span class="hljs-string">'True + 1 == 2'</span></code>.</strong></li>
 </ul>
-<div><h3 id="basicfunctions">Basic Functions</h3><pre><code class="python language-python hljs">&lt;num&gt; = pow(&lt;num&gt;, &lt;num&gt;)                         <span class="hljs-comment"># Or: &lt;number&gt; ** &lt;number&gt;</span>
-&lt;num&gt; = abs(&lt;num&gt;)                                <span class="hljs-comment"># &lt;float&gt; = abs(&lt;complex&gt;)</span>
-&lt;num&gt; = round(&lt;num&gt; [, ±ndigits])                 <span class="hljs-comment"># `round(126, -1) == 130`</span>
+<div><h3 id="builtinfunctions">Built-in Functions</h3><pre><code class="python language-python hljs">&lt;num&gt; = pow(&lt;num&gt;, &lt;num&gt;)                      <span class="hljs-comment"># E.g. `pow(2, 3) == 2 ** 3 == 8`.</span>
+&lt;num&gt; = abs(&lt;num&gt;)                             <span class="hljs-comment"># E.g. `abs(complex(3, 4)) == 5`.</span>
+&lt;num&gt; = round(&lt;num&gt; [, ±ndigits])              <span class="hljs-comment"># E.g. `round(123, -1) == 120`.</span>
+&lt;num&gt; = min(&lt;collection&gt;)                      <span class="hljs-comment"># Also max(&lt;num&gt;, &lt;num&gt; [, ...]).</span>
+&lt;num&gt; = sum(&lt;collection&gt;)                      <span class="hljs-comment"># Also math.prod(&lt;collection&gt;).</span>
 </code></pre></div>
 
-<div><h3 id="math">Math</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> e, pi, inf, nan, isinf, isnan    <span class="hljs-comment"># `&lt;el&gt; == nan` is always False.</span>
-<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> sin, cos, tan, asin, acos, atan  <span class="hljs-comment"># Also: degrees, radians.</span>
-<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> log, log10, log2                 <span class="hljs-comment"># Log can accept base as second arg.</span>
+<div><h3 id="math">Math</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> floor, ceil, trunc            <span class="hljs-comment"># They convert floats into integers.</span>
+<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> pi, inf, nan, isnan           <span class="hljs-comment"># `inf * 0` and `nan + 1` return nan.</span>
+<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> sqrt, factorial               <span class="hljs-comment"># `sqrt(-1)` will raise ValueError.</span>
+<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> sin, cos, tan                 <span class="hljs-comment"># Also: asin, acos, degrees, radians.</span>
+<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> log, log10, log2              <span class="hljs-comment"># Log accepts base as second argument.</span>
 </code></pre></div>
 
-<div><h3 id="statistics">Statistics</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> statistics <span class="hljs-keyword">import</span> mean, median, variance     <span class="hljs-comment"># Also: stdev, quantiles, groupby.</span>
+<div><h3 id="statistics">Statistics</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> statistics <span class="hljs-keyword">import</span> mean, median, mode      <span class="hljs-comment"># Mode returns the most common item.</span>
+<span class="hljs-keyword">from</span> statistics <span class="hljs-keyword">import</span> variance, stdev         <span class="hljs-comment"># Also: pvariance, pstdev, quantiles.</span>
 </code></pre></div>
 
-<div><h3 id="random">Random</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> random, randint, choice        <span class="hljs-comment"># Also: shuffle, gauss, triangular, seed.</span>
-&lt;float&gt; = random()                                <span class="hljs-comment"># A float inside [0, 1).</span>
-&lt;int&gt;   = randint(from_inc, to_inc)               <span class="hljs-comment"># An int inside [from_inc, to_inc].</span>
-&lt;el&gt;    = choice(&lt;sequence&gt;)                      <span class="hljs-comment"># Keeps the sequence intact.</span>
+<div><h3 id="random">Random</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> random, randint, uniform    <span class="hljs-comment"># Also: gauss, choice, shuffle, seed.</span>
 </code></pre></div>
 
-<div><h3 id="binhex">Bin, Hex</h3><pre><code class="python language-python hljs">&lt;int&gt; = ±<span class="hljs-number">0b</span>&lt;bin&gt;                                  <span class="hljs-comment"># Or: ±0x&lt;hex&gt;</span>
-&lt;int&gt; = int(<span class="hljs-string">'±&lt;bin&gt;'</span>, <span class="hljs-number">2</span>)                          <span class="hljs-comment"># Or: int('±&lt;hex&gt;', 16)</span>
-&lt;int&gt; = int(<span class="hljs-string">'±0b&lt;bin&gt;'</span>, <span class="hljs-number">0</span>)                        <span class="hljs-comment"># Or: int('±0x&lt;hex&gt;', 0)</span>
-&lt;str&gt; = bin(&lt;int&gt;)                                <span class="hljs-comment"># Returns '[-]0b&lt;bin&gt;'. Also hex().</span>
+<pre><code class="python language-python hljs">&lt;float&gt; = random()                             <span class="hljs-comment"># Returns a float inside [0, 1).</span>
+&lt;num&gt;   = randint/uniform(a, b)                <span class="hljs-comment"># Returns an int/float inside [a, b].</span>
+&lt;float&gt; = gauss(mean, stdev)                   <span class="hljs-comment"># Also triangular(low, high, mode).</span>
+&lt;el&gt;    = choice(&lt;sequence&gt;)                   <span class="hljs-comment"># Keeps it intact. Also sample(p, n).</span>
+shuffle(&lt;list&gt;)                                <span class="hljs-comment"># Works on all mutable sequences.</span>
+</code></pre>
+<div><h3 id="hexadecimalnumbers">Hexadecimal Numbers</h3><pre><code class="python language-python hljs">&lt;int&gt; = <span class="hljs-number">0x</span>&lt;hex&gt;                                <span class="hljs-comment"># E.g. `0xFF == 255`. Also 0b&lt;bin&gt;.</span>
+&lt;int&gt; = int(<span class="hljs-string">'±&lt;hex&gt;'</span>, <span class="hljs-number">16</span>)                      <span class="hljs-comment"># Also int('±0x&lt;hex&gt;/±0b&lt;bin&gt;', 0).</span>
+&lt;str&gt; = hex(&lt;int&gt;)                             <span class="hljs-comment"># Returns '[-]0x&lt;hex&gt;'. Also bin().</span>
 </code></pre></div>
 
-<div><h3 id="bitwiseoperators">Bitwise Operators</h3><pre><code class="python language-python hljs">&lt;int&gt; = &lt;int&gt; &amp; &lt;int&gt;                             <span class="hljs-comment"># And (0b1100 &amp; 0b1010 == 0b1000).</span>
-&lt;int&gt; = &lt;int&gt; | &lt;int&gt;                             <span class="hljs-comment"># Or  (0b1100 | 0b1010 == 0b1110).</span>
-&lt;int&gt; = &lt;int&gt; ^ &lt;int&gt;                             <span class="hljs-comment"># Xor (0b1100 ^ 0b1010 == 0b0110).</span>
-&lt;int&gt; = &lt;int&gt; &lt;&lt; n_bits                           <span class="hljs-comment"># Left shift. Use &gt;&gt; for right.</span>
-&lt;int&gt; = ~&lt;int&gt;                                    <span class="hljs-comment"># Not. Also -&lt;int&gt; - 1.</span>
+<div><h3 id="bitwiseoperators">Bitwise Operators</h3><pre><code class="python language-python hljs">&lt;int&gt; = &lt;int&gt; &amp; &lt;int&gt;                          <span class="hljs-comment"># E.g. `0b1100 &amp; 0b1010 == 0b1000`.</span>
+&lt;int&gt; = &lt;int&gt; | &lt;int&gt;                          <span class="hljs-comment"># E.g. `0b1100 | 0b1010 == 0b1110`.</span>
+&lt;int&gt; = &lt;int&gt; ^ &lt;int&gt;                          <span class="hljs-comment"># E.g. `0b1100 ^ 0b1010 == 0b0110`.</span>
+&lt;int&gt; = &lt;int&gt; &lt;&lt; n_bits                        <span class="hljs-comment"># E.g. `0b1111 &lt;&lt; 4 == 0b11110000`.</span>
+&lt;int&gt; = ~&lt;int&gt;                                 <span class="hljs-comment"># E.g. `~0b1 == -0b10 == -(0b1+1)`.</span>
 </code></pre></div>
 
 <div><h2 id="combinatorics"><a href="#combinatorics" name="combinatorics">#</a>Combinatorics</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> itertools <span class="hljs-keyword">as</span> it
 </code></pre></div>
 
-<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>list(it.product([<span class="hljs-number">0</span>, <span class="hljs-number">1</span>], repeat=<span class="hljs-number">3</span>))
-[(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">1</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>),
- (<span class="hljs-number">1</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">1</span>, <span class="hljs-number">0</span>, <span class="hljs-number">1</span>), (<span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>)]
-</code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>list(it.product(<span class="hljs-string">'abc'</span>, <span class="hljs-string">'abc'</span>))                    <span class="hljs-comment">#   a  b  c</span>
-[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),                  <span class="hljs-comment"># a x  x  x</span>
- (<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),                  <span class="hljs-comment"># b x  x  x</span>
- (<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'c'</span>)]                  <span class="hljs-comment"># c x  x  x</span>
-</code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>list(it.combinations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>))                   <span class="hljs-comment">#   a  b  c</span>
-[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),                              <span class="hljs-comment"># a .  x  x</span>
- (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>)]                                          <span class="hljs-comment"># b .  .  x</span>
+<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>list(it.product(<span class="hljs-string">'abc'</span>, repeat=<span class="hljs-number">2</span>))        <span class="hljs-comment">#   a  b  c</span>
+[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),         <span class="hljs-comment"># a x  x  x</span>
+ (<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),         <span class="hljs-comment"># b x  x  x</span>
+ (<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'c'</span>)]         <span class="hljs-comment"># c x  x  x</span>
 </code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>list(it.combinations_with_replacement(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>))  <span class="hljs-comment">#   a  b  c</span>
-[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),                  <span class="hljs-comment"># a x  x  x</span>
- (<span class="hljs-string">'b'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),                              <span class="hljs-comment"># b .  x  x</span>
- (<span class="hljs-string">'c'</span>, <span class="hljs-string">'c'</span>)]                                          <span class="hljs-comment"># c .  .  x</span>
+<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>list(it.permutations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>))          <span class="hljs-comment">#   a  b  c</span>
+[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),                     <span class="hljs-comment"># a .  x  x</span>
+ (<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),                     <span class="hljs-comment"># b x  .  x</span>
+ (<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>)]                     <span class="hljs-comment"># c x  x  .</span>
 </code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>list(it.permutations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>))                   <span class="hljs-comment">#   a  b  c</span>
-[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),                              <span class="hljs-comment"># a .  x  x</span>
- (<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),                              <span class="hljs-comment"># b x  .  x</span>
- (<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>)]                              <span class="hljs-comment"># c x  x  .</span>
+<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>list(it.combinations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>))          <span class="hljs-comment">#   a  b  c</span>
+[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),                     <span class="hljs-comment"># a .  x  x</span>
+ (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>)                                  <span class="hljs-comment"># b .  .  x</span>
+]                                            <span class="hljs-comment"># c .  .  .</span>
 </code></pre>
 <div><h2 id="datetime"><a href="#datetime" name="datetime">#</a>Datetime</h2><p><strong>Provides 'date', 'time', 'datetime' and 'timedelta' classes. All are immutable and hashable.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install python-dateutil</span>
 <span class="hljs-keyword">from</span> datetime <span class="hljs-keyword">import</span> date, time, datetime, timedelta, timezone
@@ -527,10 +536,10 @@
 &lt;TD&gt; = timedelta(weeks=<span class="hljs-number">0</span>, days=<span class="hljs-number">0</span>, hours=<span class="hljs-number">0</span>)  <span class="hljs-comment"># Also: `minutes=0, seconds=0, microseconds=0`.</span>
 </code></pre>
 <ul>
-<li><strong>Aware <code class="apache hljs"><span class="hljs-section">&lt;a&gt;</span></code> time and datetime objects have defined timezone, while naive <code class="apache hljs"><span class="hljs-section">&lt;n&gt;</span></code> don't. If object is naive, it is presumed to be in the system's timezone!</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'fold=1'</span></code> means the second pass in case of time jumping back for one hour.</strong></li>
+<li><strong>Times and datetimes that have defined timezone are called aware and ones that don't, naive. If time or datetime object is naive, it is presumed to be in the system's timezone!</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'fold=1'</span></code> means the second pass in case of time jumping back (usually for one hour).</strong></li>
 <li><strong>Timedelta normalizes arguments to ±days, seconds (&lt; 86 400) and microseconds (&lt; 1M). Its str() method returns <code class="python hljs"><span class="hljs-string">'[±D, ]H:MM:SS[.…]'</span></code> and total_seconds() a float of all seconds.</strong></li>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'&lt;D/DT&gt;.weekday()'</span></code> to get the day of the week as an int, with Monday being 0.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'&lt;D/DT&gt;.weekday()'</span></code> to get the day of the week as an integer, with Monday being 0.</strong></li>
 </ul>
 <div><h3 id="now">Now</h3><pre><code class="python language-python hljs">&lt;D/DTn&gt; = D/DT.today()                      <span class="hljs-comment"># Current local date or naive DT. Also DT.now().</span>
 &lt;DTa&gt;   = DT.now(&lt;tzinfo&gt;)                  <span class="hljs-comment"># Aware DT from current time in passed timezone.</span>
@@ -539,8 +548,8 @@
 <ul>
 <li><strong>To extract time use <code class="python hljs"><span class="hljs-string">'&lt;DTn&gt;.time()'</span></code>, <code class="python hljs"><span class="hljs-string">'&lt;DTa&gt;.time()'</span></code> or <code class="python hljs"><span class="hljs-string">'&lt;DTa&gt;.timetz()'</span></code>.</strong></li>
 </ul>
-<div><h3 id="timezone">Timezone</h3><pre><code class="python language-python apache hljs">&lt;tzinfo&gt; = timezone.utc                     <span class="hljs-comment"># London without daylight saving time (DST).</span>
-&lt;tzinfo&gt; = timezone(&lt;timedelta&gt;)            <span class="hljs-comment"># Timezone with fixed offset from UTC.</span>
+<div><h3 id="timezones">Timezones</h3><pre><code class="python language-python apache hljs">&lt;tzinfo&gt; = timezone.utc                     <span class="hljs-comment"># Coordinated universal time (UK without DST).</span>
+&lt;tzinfo&gt; = timezone(&lt;timedelta&gt;)            <span class="hljs-comment"># Timezone with fixed offset from universal time.</span>
 &lt;tzinfo&gt; = dateutil.tz.tzlocal()            <span class="hljs-comment"># Local timezone with dynamic offset from UTC.</span>
 &lt;tzinfo&gt; = zoneinfo.ZoneInfo(<span class="hljs-string">'&lt;iana_key&gt;'</span>)  <span class="hljs-comment"># 'Continent/City_Name' zone with dynamic offset.</span>
 &lt;DTa&gt;    = &lt;DT&gt;.astimezone([&lt;tzinfo&gt;])      <span class="hljs-comment"># Converts DT to the passed or local fixed zone.</span>
@@ -552,7 +561,7 @@
 <li><strong>To get ZoneInfo() to work on Windows run <code class="python hljs"><span class="hljs-string">'&gt; pip3 install tzdata'</span></code>.</strong></li>
 </ul>
 <div><h3 id="encode">Encode</h3><pre><code class="python language-python apache hljs">&lt;D/T/DT&gt; = D/T/DT.fromisoformat(&lt;str&gt;)      <span class="hljs-comment"># Object from ISO string. Raises ValueError.</span>
-&lt;DT&gt;     = DT.strptime(&lt;str&gt;, <span class="hljs-string">'&lt;format&gt;'</span>)   <span class="hljs-comment"># Datetime from str, according to format.</span>
+&lt;DT&gt;     = DT.strptime(&lt;str&gt;, <span class="hljs-string">'&lt;format&gt;'</span>)   <span class="hljs-comment"># Datetime from custom string. See Format.</span>
 &lt;D/DTn&gt;  = D/DT.fromordinal(&lt;int&gt;)          <span class="hljs-comment"># D/DT from days since the Gregorian NYE 1.</span>
 &lt;DTn&gt;    = DT.fromtimestamp(&lt;float&gt;)        <span class="hljs-comment"># Local naive DT from seconds since the Epoch.</span>
 &lt;DTa&gt;    = DT.fromtimestamp(&lt;float&gt;, &lt;tz&gt;)  <span class="hljs-comment"># Aware datetime from seconds since the Epoch.</span>
@@ -562,9 +571,9 @@
 <li><strong>ISO strings come in following forms: <code class="python hljs"><span class="hljs-string">'YYYY-MM-DD'</span></code>, <code class="python hljs"><span class="hljs-string">'HH:MM:SS.mmmuuu[±HH:MM]'</span></code>, or both separated by an arbitrary character. All parts following the hours are optional.</strong></li>
 <li><strong>Python uses the Unix Epoch: <code class="python hljs"><span class="hljs-string">'1970-01-01 00:00 UTC'</span></code>, <code class="python hljs"><span class="hljs-string">'1970-01-01 01:00 CET'</span></code>, …</strong></li>
 </ul>
-<div><h3 id="decode">Decode</h3><pre><code class="python language-python hljs">&lt;str&gt;    = &lt;D/T/DT&gt;.isoformat(sep=<span class="hljs-string">'T'</span>)      <span class="hljs-comment"># Also `timespec='auto/hours/minutes/seconds/…'`.</span>
+<div><h3 id="decode">Decode</h3><pre><code class="python language-python hljs">&lt;str&gt;    = &lt;D/T/DT&gt;.isoformat(sep=<span class="hljs-string">'T'</span>)      <span class="hljs-comment"># Also `timespec='auto/hours/minutes/seconds…'`.</span>
 &lt;str&gt;    = &lt;D/T/DT&gt;.strftime(<span class="hljs-string">'&lt;format&gt;'</span>)    <span class="hljs-comment"># Custom string representation of the object.</span>
-&lt;int&gt;    = &lt;D/DT&gt;.toordinal()               <span class="hljs-comment"># Days since Gregorian NYE 1, ignoring time and tz.</span>
+&lt;int&gt;    = &lt;D/DT&gt;.toordinal()               <span class="hljs-comment"># Days since NYE 1. Ignores DT's time and zone.</span>
 &lt;float&gt;  = &lt;DTn&gt;.timestamp()                <span class="hljs-comment"># Seconds since the Epoch, from local naive DT.</span>
 &lt;float&gt;  = &lt;DTa&gt;.timestamp()                <span class="hljs-comment"># Seconds since the Epoch, from aware datetime.</span>
 </code></pre></div>
@@ -575,44 +584,43 @@
 </code></pre></div>
 
 <ul>
-<li><strong><code class="python hljs"><span class="hljs-string">'%z'</span></code> accepts <code class="python hljs"><span class="hljs-string">'±HH[:]MM'</span></code> and returns <code class="python hljs"><span class="hljs-string">'±HHMM'</span></code> or empty string if datetime is naive.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'%Z'</span></code> accepts <code class="python hljs"><span class="hljs-string">'UTC/GMT'</span></code> and local timezone's code and returns timezone's name, <code class="python hljs"><span class="hljs-string">'UTC[±HH:MM]'</span></code> if timezone is nameless, or an empty string if datetime is naive.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'%z'</span></code> accepts <code class="python hljs"><span class="hljs-string">'±HH[:]MM'</span></code> and returns <code class="python hljs"><span class="hljs-string">'±HHMM'</span></code> or empty string if object is naive.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'%Z'</span></code> accepts <code class="python hljs"><span class="hljs-string">'UTC/GMT'</span></code> and local timezone's code and returns timezone's name, <code class="python hljs"><span class="hljs-string">'UTC[±HH:MM]'</span></code> if timezone is nameless, or an empty string if object is naive.</strong></li>
 </ul>
 <div><h3 id="arithmetics">Arithmetics</h3><pre><code class="python language-python apache hljs">&lt;bool&gt;   = &lt;D/T/DTn&gt; &gt; &lt;D/T/DTn&gt;            <span class="hljs-comment"># Ignores time jumps (fold attribute). Also ==.</span>
-&lt;bool&gt;   = &lt;DTa&gt;     &gt; &lt;DTa&gt;                <span class="hljs-comment"># Ignores jumps if they share tz object. Broken ==.</span>
+&lt;bool&gt;   = &lt;DTa&gt;     &gt; &lt;DTa&gt;                <span class="hljs-comment"># Ignores time jumps if they share tzinfo object.</span>
 &lt;TD&gt;     = &lt;D/DTn&gt;   - &lt;D/DTn&gt;              <span class="hljs-comment"># Ignores jumps. Convert to UTC for actual delta.</span>
-&lt;TD&gt;     = &lt;DTa&gt;     - &lt;DTa&gt;                <span class="hljs-comment"># Ignores jumps if they share tzinfo object.</span>
+&lt;TD&gt;     = &lt;DTa&gt;     - &lt;DTa&gt;                <span class="hljs-comment"># Ignores jumps if they share the tzinfo object.</span>
 &lt;D/DT&gt;   = &lt;D/DT&gt;    ± &lt;TD&gt;                 <span class="hljs-comment"># Returned datetime can fall into missing hour.</span>
-&lt;TD&gt;     = &lt;TD&gt;      * &lt;float&gt;              <span class="hljs-comment"># Also: &lt;TD&gt; = abs(&lt;TD&gt;) and &lt;TD&gt; = &lt;TD&gt; ±% &lt;TD&gt;.</span>
-&lt;float&gt;  = &lt;TD&gt;      / &lt;TD&gt;                 <span class="hljs-comment"># E.g. how many hours are in TD. Also //, divmod().</span>
+&lt;TD&gt;     = &lt;TD&gt;      * &lt;float&gt;              <span class="hljs-comment"># Also `&lt;TD&gt; = abs(&lt;TD&gt;)`, `&lt;TD&gt; = &lt;TD&gt; ± &lt;TD&gt;`.</span>
+&lt;float&gt;  = &lt;TD&gt;      / &lt;TD&gt;                 <span class="hljs-comment"># Also `(&lt;int&gt;, &lt;TD&gt;) = divmod(&lt;TD&gt;, &lt;TD&gt;)`.</span>
 </code></pre></div>
 
-<div><h2 id="arguments"><a href="#arguments" name="arguments">#</a>Arguments</h2><div><h3 id="insidefunctioncall">Inside Function Call</h3><pre><code class="python language-python hljs">func(&lt;positional_args&gt;)                           <span class="hljs-comment"># func(0, 0)</span>
-func(&lt;keyword_args&gt;)                              <span class="hljs-comment"># func(x=0, y=0)</span>
-func(&lt;positional_args&gt;, &lt;keyword_args&gt;)           <span class="hljs-comment"># func(0, y=0)</span>
-</code></pre></div></div>
-
-
-<div><h3 id="insidefunctiondefinition">Inside Function Definition</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">func</span><span class="hljs-params">(&lt;nondefault_args&gt;)</span>:</span> ...                  <span class="hljs-comment"># def func(x, y): ...</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">func</span><span class="hljs-params">(&lt;default_args&gt;)</span>:</span> ...                     <span class="hljs-comment"># def func(x=0, y=0): ...</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">func</span><span class="hljs-params">(&lt;nondefault_args&gt;, &lt;default_args&gt;)</span>:</span> ...  <span class="hljs-comment"># def func(x, y=0): ...</span>
+<div><h2 id="function"><a href="#function" name="function">#</a>Function</h2><p><strong>Independent block of code that returns a value when called.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> &lt;<span class="hljs-title">func_name</span>&gt;<span class="hljs-params">(&lt;nondefault_args&gt;)</span>:</span> ...                  <span class="hljs-comment"># E.g. `def func(x, y): ...`.</span>
+<span class="hljs-function"><span class="hljs-keyword">def</span> &lt;<span class="hljs-title">func_name</span>&gt;<span class="hljs-params">(&lt;default_args&gt;)</span>:</span> ...                     <span class="hljs-comment"># E.g. `def func(x=0, y=0): ...`.</span>
+<span class="hljs-function"><span class="hljs-keyword">def</span> &lt;<span class="hljs-title">func_name</span>&gt;<span class="hljs-params">(&lt;nondefault_args&gt;, &lt;default_args&gt;)</span>:</span> ...  <span class="hljs-comment"># E.g. `def func(x, y=0): ...`.</span>
 </code></pre></div>
 
+
 <ul>
-<li><strong>Default values are evaluated when function is first encountered in the scope.</strong></li>
-<li><strong>Any mutation of a mutable default value will persist between invocations!</strong></li>
+<li><strong>Function returns None if it doesn't encounter <code class="python hljs"><span class="hljs-string">'return &lt;obj/exp&gt;'</span></code> statement.</strong></li>
+<li><strong>Run <code class="python hljs"><span class="hljs-string">'global &lt;var_name&gt;'</span></code> inside the function before assigning to global variable.</strong></li>
+<li><strong>Default values are evaluated when function is first encountered in the scope. Any mutation of a mutable default value will persist between invocations!</strong></li>
 </ul>
-<div><h2 id="splatoperator"><a href="#splatoperator" name="splatoperator">#</a>Splat Operator</h2><div><h3 id="insidefunctioncall-1">Inside Function Call</h3><p><strong>Splat expands a collection into positional arguments, while splatty-splat expands a dictionary into keyword arguments.</strong></p><pre><code class="python language-python hljs">args   = (<span class="hljs-number">1</span>, <span class="hljs-number">2</span>)
-kwargs = {<span class="hljs-string">'x'</span>: <span class="hljs-number">3</span>, <span class="hljs-string">'y'</span>: <span class="hljs-number">4</span>, <span class="hljs-string">'z'</span>: <span class="hljs-number">5</span>}
-func(*args, **kwargs)
-</code></pre></div></div>
+<div><h3 id="functioncall">Function Call</h3><pre><code class="python language-python hljs">&lt;obj&gt; = &lt;function&gt;(&lt;positional_args&gt;)                    <span class="hljs-comment"># E.g. `func(0, 0)`.</span>
+&lt;obj&gt; = &lt;function&gt;(&lt;keyword_args&gt;)                       <span class="hljs-comment"># E.g. `func(x=0, y=0)`.</span>
+&lt;obj&gt; = &lt;function&gt;(&lt;positional_args&gt;, &lt;keyword_args&gt;)    <span class="hljs-comment"># E.g. `func(0, y=0)`.</span>
+</code></pre></div>
 
+<div><h2 id="splatoperator"><a href="#splatoperator" name="splatoperator">#</a>Splat Operator</h2><p><strong>Splat expands a collection into positional arguments, while splatty-splat expands a dictionary into keyword arguments.</strong></p><pre><code class="python language-python hljs">args, kwargs = (<span class="hljs-number">1</span>, <span class="hljs-number">2</span>), {<span class="hljs-string">'z'</span>: <span class="hljs-number">3</span>}
+func(*args, **kwargs)
+</code></pre></div>
 
 
-<div><h4 id="isthesameas">Is the same as:</h4><pre><code class="python language-python hljs">func(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, x=<span class="hljs-number">3</span>, y=<span class="hljs-number">4</span>, z=<span class="hljs-number">5</span>)
+<div><h4 id="isthesameas">Is the same as:</h4><pre><code class="python language-python hljs">func(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, z=<span class="hljs-number">3</span>)
 </code></pre></div>
 
-<div><h3 id="insidefunctiondefinition-1">Inside Function Definition</h3><p><strong>Splat combines zero or more positional arguments into a tuple, while splatty-splat combines zero or more keyword arguments into a dictionary.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(*a)</span>:</span>
+<div><h3 id="insidefunctiondefinition">Inside Function Definition</h3><p><strong>Splat combines zero or more positional arguments into a tuple, while splatty-splat combines zero or more keyword arguments into a dictionary.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(*a)</span>:</span>
     <span class="hljs-keyword">return</span> sum(a)
 </code></pre></div>
 
@@ -620,39 +628,32 @@
 <pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>add(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
 <span class="hljs-number">6</span>
 </code></pre>
-<div><h4 id="legalargumentcombinations">Legal argument combinations:</h4><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args)</span>:</span> ...               <span class="hljs-comment"># f(1, 2, 3)</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args)</span>:</span> ...            <span class="hljs-comment"># f(1, 2, 3)</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, z)</span>:</span> ...            <span class="hljs-comment"># f(1, 2, z=3)</span>
+<div><h4 id="allowedcompositionsofargumentsandthewaystheycanbecalled">Allowed compositions of arguments and the ways they can be called:</h4><pre><code class="text language-text">┏━━━━━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┓
+┃                           │  func(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>)  │ func(<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>) │ func(x=<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>) ┃
+┠───────────────────────────┼──────────────┼──────────────┼────────────────┨
+┃ <span class="hljs-title">func</span>(x, *args, **kwargs): │      ✓       │      ✓       │       ✓        ┃
+┃ <span class="hljs-title">func</span>(*args, y, **kwargs): │              │      ✓       │       ✓        ┃
+┃ <span class="hljs-title">func</span>(*, x, **kwargs):     │              │              │       ✓        ┃
+┗━━━━━━━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┛
 </code></pre></div>
 
-<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(**kwargs)</span>:</span> ...            <span class="hljs-comment"># f(x=1, y=2, z=3)</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, **kwargs)</span>:</span> ...         <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3)</span>
-</code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, **kwargs)</span>:</span> ...     <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args, **kwargs)</span>:</span> ...  <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, y, **kwargs)</span>:</span> ...  <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3)</span>
-</code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*, x, y, z)</span>:</span> ...          <span class="hljs-comment"># f(x=1, y=2, z=3)</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *, y, z)</span>:</span> ...          <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3)</span>
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, y, *, z)</span>:</span> ...          <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3)</span>
-</code></pre>
-<div><h3 id="otheruses">Other Uses</h3><pre><code class="python language-python hljs">&lt;list&gt;  = [*&lt;coll.&gt; [, ...]]    <span class="hljs-comment"># Or: list(&lt;collection&gt;) [+ ...]</span>
-&lt;tuple&gt; = (*&lt;coll.&gt;, [...])     <span class="hljs-comment"># Or: tuple(&lt;collection&gt;) [+ ...]</span>
-&lt;set&gt;   = {*&lt;coll.&gt; [, ...]}    <span class="hljs-comment"># Or: set(&lt;collection&gt;) [| ...]</span>
-&lt;dict&gt;  = {**&lt;dict&gt; [, ...]}    <span class="hljs-comment"># Or: &lt;dict&gt; | ...</span>
+<div><h3 id="otheruses">Other Uses</h3><pre><code class="python language-python hljs">&lt;list&gt;  = [*&lt;collection&gt; [, ...]]  <span class="hljs-comment"># Or: list(&lt;coll&gt;) [+ ...]</span>
+&lt;tuple&gt; = (*&lt;collection&gt;, [...])   <span class="hljs-comment"># Or: tuple(&lt;coll&gt;) [+ ...]</span>
+&lt;set&gt;   = {*&lt;collection&gt; [, ...]}  <span class="hljs-comment"># Or: set(&lt;coll&gt;) [| ...]</span>
+&lt;dict&gt;  = {**&lt;dict&gt; [, ...]}       <span class="hljs-comment"># Or: &lt;dict&gt; | ...</span>
 </code></pre></div>
 
-<pre><code class="python language-python hljs">head, *body, tail = &lt;coll.&gt;     <span class="hljs-comment"># Head or tail can be omitted.</span>
+<pre><code class="python language-python hljs">head, *body, tail = &lt;collection&gt;   <span class="hljs-comment"># Head or tail can be omitted.</span>
 </code></pre>
 <div><h2 id="inline"><a href="#inline" name="inline">#</a>Inline</h2><div><h3 id="lambda">Lambda</h3><pre><code class="python language-python hljs">&lt;func&gt; = <span class="hljs-keyword">lambda</span>: &lt;return_value&gt;                     <span class="hljs-comment"># A single statement function.</span>
 &lt;func&gt; = <span class="hljs-keyword">lambda</span> &lt;arg_1&gt;, &lt;arg_2&gt;: &lt;return_value&gt;    <span class="hljs-comment"># Also allows default arguments.</span>
 </code></pre></div></div>
 
 
-<div><h3 id="comprehensions">Comprehensions</h3><pre><code class="python language-python hljs">&lt;list&gt; = [i+<span class="hljs-number">1</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)]                   <span class="hljs-comment"># Or: [1, 2, ..., 10]</span>
-&lt;iter&gt; = (i <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>) <span class="hljs-keyword">if</span> i &gt; <span class="hljs-number">5</span>)            <span class="hljs-comment"># Or: iter([6, 7, 8, 9])</span>
-&lt;set&gt;  = {i+<span class="hljs-number">5</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)}                   <span class="hljs-comment"># Or: {5, 6, ..., 14}</span>
-&lt;dict&gt; = {i: i*<span class="hljs-number">2</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)}                <span class="hljs-comment"># Or: {0: 0, 1: 2, ..., 9: 18}</span>
+<div><h3 id="comprehensions">Comprehensions</h3><pre><code class="python language-python hljs">&lt;list&gt; = [i+<span class="hljs-number">1</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)]                   <span class="hljs-comment"># Returns [1, 2, ..., 10].</span>
+&lt;iter&gt; = (i <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>) <span class="hljs-keyword">if</span> i &gt; <span class="hljs-number">5</span>)            <span class="hljs-comment"># Returns iter([6, 7, 8, 9]).</span>
+&lt;set&gt;  = {i+<span class="hljs-number">5</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)}                   <span class="hljs-comment"># Returns {5, 6, ..., 14}.</span>
+&lt;dict&gt; = {i: i*<span class="hljs-number">2</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)}                <span class="hljs-comment"># Returns {0: 0, 1: 2, ..., 9: 18}.</span>
 </code></pre></div>
 
 <pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>[l+r <span class="hljs-keyword">for</span> l <span class="hljs-keyword">in</span> <span class="hljs-string">'abc'</span> <span class="hljs-keyword">for</span> r <span class="hljs-keyword">in</span> <span class="hljs-string">'abc'</span>]             <span class="hljs-comment"># Inner loop is on the right side.</span>
@@ -661,9 +662,9 @@
 <div><h3 id="mapfilterreduce">Map, Filter, Reduce</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> reduce
 </code></pre></div>
 
-<pre><code class="python language-python hljs">&lt;iter&gt; = map(<span class="hljs-keyword">lambda</span> x: x + <span class="hljs-number">1</span>, range(<span class="hljs-number">10</span>))            <span class="hljs-comment"># Or: iter([1, 2, ..., 10])</span>
-&lt;iter&gt; = filter(<span class="hljs-keyword">lambda</span> x: x &gt; <span class="hljs-number">5</span>, range(<span class="hljs-number">10</span>))         <span class="hljs-comment"># Or: iter([6, 7, 8, 9])</span>
-&lt;obj&gt;  = reduce(<span class="hljs-keyword">lambda</span> out, x: out + x, range(<span class="hljs-number">10</span>))  <span class="hljs-comment"># Or: 45</span>
+<pre><code class="python language-python hljs">&lt;iter&gt; = map(<span class="hljs-keyword">lambda</span> x: x + <span class="hljs-number">1</span>, range(<span class="hljs-number">10</span>))            <span class="hljs-comment"># Returns iter([1, 2, ..., 10]).</span>
+&lt;iter&gt; = filter(<span class="hljs-keyword">lambda</span> x: x &gt; <span class="hljs-number">5</span>, range(<span class="hljs-number">10</span>))         <span class="hljs-comment"># Returns iter([6, 7, 8, 9]).</span>
+&lt;obj&gt;  = reduce(<span class="hljs-keyword">lambda</span> out, x: out + x, range(<span class="hljs-number">10</span>))  <span class="hljs-comment"># Returns 45.</span>
 </code></pre>
 <div><h3 id="anyall">Any, All</h3><pre><code class="python language-python hljs">&lt;bool&gt; = any(&lt;collection&gt;)                          <span class="hljs-comment"># Is `bool(&lt;el&gt;)` True for any el?</span>
 &lt;bool&gt; = all(&lt;collection&gt;)                          <span class="hljs-comment"># True for all? Also True if empty.</span>
@@ -672,22 +673,30 @@
 <div><h3 id="conditionalexpression">Conditional Expression</h3><pre><code class="python language-python hljs">&lt;obj&gt; = &lt;exp&gt; <span class="hljs-keyword">if</span> &lt;condition&gt; <span class="hljs-keyword">else</span> &lt;exp&gt;             <span class="hljs-comment"># Only one expression is evaluated.</span>
 </code></pre></div>
 
-<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>[a <span class="hljs-keyword">if</span> a <span class="hljs-keyword">else</span> <span class="hljs-string">'zero'</span> <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)]      <span class="hljs-comment"># `any([0, '', [], None]) == False`</span>
+<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>[i <span class="hljs-keyword">if</span> i <span class="hljs-keyword">else</span> <span class="hljs-string">'zero'</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)]      <span class="hljs-comment"># `any([0, '', [], None]) == False`</span>
 [<span class="hljs-string">'zero'</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]
 </code></pre>
+<div><h3 id="andor">And, Or</h3><pre><code class="python language-python hljs">&lt;obj&gt; = &lt;exp&gt; <span class="hljs-keyword">and</span> &lt;exp&gt; [<span class="hljs-keyword">and</span> ...]                   <span class="hljs-comment"># Returns first false or last object.</span>
+&lt;obj&gt; = &lt;exp&gt; <span class="hljs-keyword">or</span> &lt;exp&gt; [<span class="hljs-keyword">or</span> ...]                     <span class="hljs-comment"># Returns first true or last object.</span>
+</code></pre></div>
+
+<div><h3 id="walrusoperator">Walrus Operator</h3><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>[i <span class="hljs-keyword">for</span> ch <span class="hljs-keyword">in</span> <span class="hljs-string">'0123'</span> <span class="hljs-keyword">if</span> (i := int(ch)) &gt; <span class="hljs-number">0</span>]      <span class="hljs-comment"># Assigns to variable mid-sentence.</span>
+[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]
+</code></pre></div>
+
 <div><h3 id="namedtupleenumdataclass">Named Tuple, Enum, Dataclass</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
-Point = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>)                  <span class="hljs-comment"># Creates a tuple's subclass.</span>
+Point = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>)                  <span class="hljs-comment"># Creates tuple's subclass.</span>
 point = Point(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>)                                 <span class="hljs-comment"># Returns its instance.</span>
-</code></pre></div>
 
-<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum
-Direction = Enum(<span class="hljs-string">'Direction'</span>, <span class="hljs-string">'N E S W'</span>)            <span class="hljs-comment"># Creates an enum.</span>
+<span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum
+Direction = Enum(<span class="hljs-string">'Direction'</span>, <span class="hljs-string">'N E S W'</span>)            <span class="hljs-comment"># Creates Enum's subclass.</span>
 direction = Direction.N                             <span class="hljs-comment"># Returns its member.</span>
-</code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> dataclasses <span class="hljs-keyword">import</span> make_dataclass
+
+<span class="hljs-keyword">from</span> dataclasses <span class="hljs-keyword">import</span> make_dataclass
 Player = make_dataclass(<span class="hljs-string">'Player'</span>, [<span class="hljs-string">'loc'</span>, <span class="hljs-string">'dir'</span>])   <span class="hljs-comment"># Creates a class.</span>
 player = Player(point, direction)                   <span class="hljs-comment"># Returns its instance.</span>
-</code></pre>
+</code></pre></div>
+
 <div><h2 id="imports"><a href="#imports" name="imports">#</a>Imports</h2><p><strong>Mechanism that makes code in one file available to another file.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> &lt;module&gt;            <span class="hljs-comment"># Imports a built-in or '&lt;module&gt;.py'.</span>
 <span class="hljs-keyword">import</span> &lt;package&gt;           <span class="hljs-comment"># Imports a built-in or '&lt;package&gt;/__init__.py'.</span>
 <span class="hljs-keyword">import</span> &lt;package&gt;.&lt;module&gt;  <span class="hljs-comment"># Imports a built-in or '&lt;package&gt;/&lt;module&gt;.py'.</span>
@@ -695,13 +704,13 @@
 
 
 <ul>
-<li><strong>Package is a collection of modules, but it can also define its own objects.</strong></li>
+<li><strong>Package is a collection of modules, but it can also define its own functions, classes, etc.</strong></li>
 <li><strong>On a filesystem this corresponds to a directory of Python files with an optional init script.</strong></li>
-<li><strong>Running <code class="python hljs"><span class="hljs-string">'import &lt;package&gt;'</span></code> does not automatically provide access to the package's modules unless they are explicitly imported in its init script.</strong></li>
+<li><strong>Running <code class="python hljs"><span class="hljs-string">'import &lt;package&gt;'</span></code> does not automatically provide access to the package's modules unless they are explicitly imported in the <code class="python hljs"><span class="hljs-string">'&lt;package&gt;/__init__.py'</span></code> script.</strong></li>
 <li><strong>Directory of the file that is passed to python command serves as a root of local imports.</strong></li>
 <li><strong>For relative imports use <code class="python hljs"><span class="hljs-string">'from .[…][&lt;pkg/module&gt;[.…]] import &lt;obj&gt;'</span></code>.</strong></li>
 </ul>
-<div><h2 id="closure"><a href="#closure" name="closure">#</a>Closure</h2><p><strong>We have/get a closure in Python when a nested function references a value of its enclosing function and then the enclosing function returns the nested function.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_multiplier</span><span class="hljs-params">(a)</span>:</span>
+<div><h2 id="closure"><a href="#closure" name="closure">#</a>Closure</h2><p><strong>We have/get a closure in Python when a nested function references a value of its enclosing function and then the enclosing function returns its nested function.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_multiplier</span><span class="hljs-params">(a)</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(b)</span>:</span>
         <span class="hljs-keyword">return</span> a * b
     <span class="hljs-keyword">return</span> out
@@ -726,8 +735,7 @@
 <span class="hljs-number">30</span>
 </code></pre>
 <ul>
-<li><strong>Partial is also useful in cases when a function needs to be passed as an argument because it enables us to set its arguments beforehand.</strong></li>
-<li><strong>A few examples being: <code class="python hljs"><span class="hljs-string">'defaultdict(&lt;func&gt;)'</span></code>, <code class="python hljs"><span class="hljs-string">'iter(&lt;func&gt;, to_exc)'</span></code> and dataclass's <code class="python hljs"><span class="hljs-string">'field(default_factory=&lt;func&gt;)'</span></code>.</strong></li>
+<li><strong>Partial is also useful in cases when a function needs to be passed as an argument because it enables us to set its arguments beforehand (<code class="python hljs"><span class="hljs-string">'collections.defaultdict(&lt;func&gt;)'</span></code>, <code class="python hljs"><span class="hljs-string">'iter(&lt;func&gt;, to_exc)'</span></code> and <code class="python hljs"><span class="hljs-string">'dataclasses.field(default_factory=&lt;func&gt;)'</span></code>).</strong></li>
 </ul>
 <div><h3 id="nonlocal">Non-Local</h3><p><strong>If variable is being assigned to anywhere in the scope, it is regarded as a local variable, unless it is declared as a 'global' or a 'nonlocal'.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_counter</span><span class="hljs-params">()</span>:</span>
     i = <span class="hljs-number">0</span>
@@ -743,10 +751,7 @@
 <span class="hljs-meta">&gt;&gt;&gt; </span>counter(), counter(), counter()
 (<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
 </code></pre>
-<div class="pagebreak"></div><div><h2 id="decorator"><a href="#decorator" name="decorator">#</a>Decorator</h2><ul>
-<li><strong>A decorator takes a function, adds some functionality and returns it.</strong></li>
-<li><strong>It can be any <a href="#callable">callable</a>, but is usually implemented as a function that returns a <a href="#closure">closure</a>.</strong></li>
-</ul><pre><code class="python language-python hljs"><span class="hljs-meta">@decorator_name</span>
+<div class="pagebreak"></div><div><h2 id="decorator"><a href="#decorator" name="decorator">#</a>Decorator</h2><p><strong>A decorator takes a function, adds some functionality and returns it. It can be any <a href="#callable">callable</a>, but is usually implemented as a function that returns a <a href="#closure">closure</a>.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">@decorator_name</span>
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">function_that_gets_passed_to_decorator</span><span class="hljs-params">()</span>:</span>
     ...
 </code></pre></div>
@@ -778,7 +783,7 @@
 
 
 <ul>
-<li><strong>Potential problem with cache is that it can grow indefinitely. To clear its stored values run <code class="python hljs"><span class="hljs-string">'fib.cache_clear()'</span></code>, or use <code class="python hljs"><span class="hljs-string">'@lru_cache(maxsize=&lt;int&gt;)'</span></code> decorator instead.</strong></li>
+<li><strong>Potential problem with cache is that it can grow indefinitely. To clear stored values run <code class="python hljs"><span class="hljs-string">'&lt;func&gt;.cache_clear()'</span></code>, or use <code class="python hljs"><span class="hljs-string">'@lru_cache(maxsize=&lt;int&gt;)'</span></code> decorator instead.</strong></li>
 <li><strong>CPython interpreter limits recursion depth to 3000 by default. To increase it run <code class="python hljs"><span class="hljs-string">'sys.setrecursionlimit(&lt;int&gt;)'</span></code>.</strong></li>
 </ul>
 <div><h3 id="parametrizeddecorator">Parametrized Decorator</h3><p><strong>A decorator that accepts arguments and returns a normal decorator that accepts a function.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> wraps
@@ -817,56 +822,59 @@
 </code></pre></div>
 
 
-<ul>
-<li><strong>Return value of str() should be readable and of repr() unambiguous.</strong></li>
-<li><strong>If only repr() is defined, it will also be used for str().</strong></li>
-<li><strong>Methods decorated with <code class="python hljs"><span class="hljs-string">'@staticmethod'</span></code> do not receive 'self' nor 'cls' as their first arg.</strong></li>
-</ul>
 <pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>obj = MyClass(<span class="hljs-number">1</span>)
 <span class="hljs-meta">&gt;&gt;&gt; </span>obj.a, str(obj), repr(obj)
 (<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>, <span class="hljs-string">'MyClass(1)'</span>)
 </code></pre>
+<ul>
+<li><strong>Methods whose names start and end with two underscores are called special methods. They are executed when object is passed to a built-in function or used as an operand, for&nbsp;example, <code class="python hljs"><span class="hljs-string">'print(a)'</span></code> calls <code class="python hljs"><span class="hljs-string">'a.__str__()'</span></code> and <code class="python hljs"><span class="hljs-string">'a + b'</span></code> calls <code class="python hljs"><span class="hljs-string">'a.__add__(b)'</span></code>.</strong></li>
+<li><strong>Methods decorated with <code class="python hljs"><span class="hljs-string">'@staticmethod'</span></code> receive neither 'self' nor 'cls' argument.</strong></li>
+<li><strong>Return value of str() special method should be readable and of repr() unambiguous. If only repr() is defined, it will also be used for str().</strong></li>
+</ul>
 <div><h4 id="expressionsthatcallthestrmethod">Expressions that call the str() method:</h4><pre><code class="python language-python hljs">print(&lt;obj&gt;)
 <span class="hljs-string">f'<span class="hljs-subst">{&lt;obj&gt;}</span>'</span>
 logging.warning(&lt;obj&gt;)
 csv.writer(&lt;file&gt;).writerow([&lt;obj&gt;])
-<span class="hljs-keyword">raise</span> Exception(&lt;obj&gt;)
 </code></pre></div>
 
 <div><h4 id="expressionsthatcallthereprmethod">Expressions that call the repr() method:</h4><pre><code class="python language-python hljs">print/str/repr([&lt;obj&gt;])
 print/str/repr({&lt;obj&gt;: &lt;obj&gt;})
 <span class="hljs-string">f'<span class="hljs-subst">{&lt;obj&gt;!r}</span>'</span>
-Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span class="hljs-string">'a'</span>]); print/str/repr(Z(&lt;obj&gt;))
-<span class="hljs-meta">&gt;&gt;&gt; </span>&lt;obj&gt;
+Z = make_dataclass(<span class="hljs-string">'Z'</span>, [<span class="hljs-string">'a'</span>]); print/str/repr(Z(&lt;obj&gt;))
 </code></pre></div>
 
-<div><h3 id="inheritance">Inheritance</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
+<div><h3 id="subclass">Subclass</h3><ul>
+<li><strong>Inheritance is a mechanism that enables a class to extend some other class (that is, subclass to extend its parent), and by doing so inherit all of its methods and attributes.</strong></li>
+<li><strong>Subclass can then add its own methods and attributes or override inherited ones by reusing their names.</strong></li>
+</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name)</span>:</span>
         self.name = name
+    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__repr__</span><span class="hljs-params">(self)</span>:</span>
+        <span class="hljs-keyword">return</span> <span class="hljs-string">f'Person(<span class="hljs-subst">{self.name!r}</span>)'</span>
+    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__lt__</span><span class="hljs-params">(self, other)</span>:</span>
+        <span class="hljs-keyword">return</span> self.name &lt; other.name
 
 <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Employee</span><span class="hljs-params">(Person)</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name, staff_num)</span>:</span>
         super().__init__(name)
         self.staff_num = staff_num
+    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__repr__</span><span class="hljs-params">(self)</span>:</span>
+        <span class="hljs-keyword">return</span> <span class="hljs-string">f'Employee(<span class="hljs-subst">{self.name!r}</span>, <span class="hljs-subst">{self.staff_num}</span>)'</span>
 </code></pre></div>
 
-<div><h4 id="multipleinheritance">Multiple inheritance:</h4><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">A</span>:</span> <span class="hljs-keyword">pass</span>
-<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">B</span>:</span> <span class="hljs-keyword">pass</span>
-<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">C</span><span class="hljs-params">(A, B)</span>:</span> <span class="hljs-keyword">pass</span>
-</code></pre></div>
 
-<p><strong>MRO determines the order in which parent classes are traversed when searching for a method or an attribute:</strong></p>
-<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>C.mro()
-[&lt;<span class="hljs-class"><span class="hljs-title">class</span> '<span class="hljs-title">C</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">A</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">B</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">object</span>'&gt;]
-</span></code></pre>
+<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>people = {Person(<span class="hljs-string">'Ann'</span>), Employee(<span class="hljs-string">'Bob'</span>, <span class="hljs-number">0</span>)}
+<span class="hljs-meta">&gt;&gt;&gt; </span>sorted(people)
+[Person(<span class="hljs-string">'Ann'</span>), Employee(<span class="hljs-string">'Bob'</span>, <span class="hljs-number">0</span>)]
+</code></pre>
 <div><h3 id="typeannotations">Type Annotations</h3><ul>
 <li><strong>They add type hints to variables, arguments and functions (<code class="python hljs"><span class="hljs-string">'def f() -&gt; &lt;type&gt;:'</span></code>).</strong></li>
 <li><strong>Hints are used by type checkers like <a href="https://pypi.org/project/mypy/">mypy</a>, data validation libraries such as <a href="https://pypi.org/project/pydantic/">Pydantic</a> and lately also by <a href="https://pypi.org/project/Cython/">Cython</a> compiler. However, they are not enforced by CPython interpreter.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> abc
 
-&lt;name&gt;: &lt;type&gt; [| ...] [= &lt;obj&gt;]                              <span class="hljs-comment"># `|` since 3.10.</span>
-&lt;name&gt;: list/set/abc.Iterable/abc.Sequence[&lt;type&gt;] [= &lt;obj&gt;]  <span class="hljs-comment"># Since 3.9.</span>
-&lt;name&gt;: dict/tuple[&lt;type&gt;, ...] [= &lt;obj&gt;]                     <span class="hljs-comment"># Since 3.9.</span>
+&lt;name&gt;: &lt;type&gt; [| ...] [= &lt;obj&gt;]
+&lt;name&gt;: list/set/abc.Iterable/abc.Sequence[&lt;type&gt;] [= &lt;obj&gt;]
+&lt;name&gt;: tuple/dict[&lt;type&gt;, ...] [= &lt;obj&gt;]
 </code></pre></div>
 
 
@@ -883,12 +891,13 @@
 <ul>
 <li><strong>Objects can be made <a href="#sortable">sortable</a> with <code class="python hljs"><span class="hljs-string">'order=True'</span></code> and immutable with <code class="python hljs"><span class="hljs-string">'frozen=True'</span></code>.</strong></li>
 <li><strong>For object to be <a href="#hashable">hashable</a>, all attributes must be hashable and 'frozen' must be True.</strong></li>
-<li><strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">'&lt;attr_name&gt;: list = []'</span></code> would make a list that is shared among all instances. Its 'default_factory' argument can be any <a href="#callable">callable</a>.</strong></li>
+<li><strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">'&lt;attr_name&gt;: list = []'</span></code> would make a list that is shared among all instances. Its 'default_factory' argument accepts any <a href="#callable">callable</a> object.</strong></li>
 <li><strong>For attributes of arbitrary type use <code class="python hljs"><span class="hljs-string">'typing.Any'</span></code>.</strong></li>
 </ul>
-<pre><code class="python language-python hljs">&lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_attribute_names&gt;)
-&lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_tuples&gt;)
-&lt;tuple&gt; = (<span class="hljs-string">'&lt;attr_name&gt;'</span>, &lt;type&gt; [, &lt;default_value&gt;])</code></pre>
+<pre><code class="python language-python hljs">P = make_dataclass(<span class="hljs-string">'P'</span>, [<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>])
+P = make_dataclass(<span class="hljs-string">'P'</span>, [(<span class="hljs-string">'x'</span>, float), (<span class="hljs-string">'y'</span>, float)])
+P = make_dataclass(<span class="hljs-string">'P'</span>, [(<span class="hljs-string">'x'</span>, float, <span class="hljs-number">0</span>), (<span class="hljs-string">'y'</span>, float, <span class="hljs-number">0</span>)])
+</code></pre>
 <div><h3 id="property">Property</h3><p><strong>Pythonic way of implementing getters and setters.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
 <span class="hljs-meta">    @property</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">name</span><span class="hljs-params">(self)</span>:</span>
@@ -905,7 +914,7 @@
 <span class="hljs-meta">&gt;&gt;&gt; </span>person.name
 <span class="hljs-string">'Guido van Rossum'</span>
 </code></pre>
-<div><h3 id="slots">Slots</h3><p><strong>Mechanism that restricts objects to attributes listed in 'slots', reduces their memory footprint.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClassWithSlots</span>:</span>
+<div><h3 id="slots">Slots</h3><p><strong>Mechanism that restricts objects to attributes listed in 'slots'.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClassWithSlots</span>:</span>
     __slots__ = [<span class="hljs-string">'a'</span>]
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
         self.a = <span class="hljs-number">1</span>
@@ -917,9 +926,8 @@
 </code></pre></div>
 
 <div><h2 id="ducktypes"><a href="#ducktypes" name="ducktypes">#</a>Duck Types</h2><p><strong>A duck type is an implicit type that prescribes a set of special methods. Any object that has those methods defined is considered a member of that duck type.</strong></p><div><h3 id="comparable">Comparable</h3><ul>
-<li><strong>If eq() method is not overridden, it returns <code class="python hljs"><span class="hljs-string">'id(self) == id(other)'</span></code>, which is the same as <code class="python hljs"><span class="hljs-string">'self is other'</span></code>.</strong></li>
-<li><strong>That means all objects compare not equal by default.</strong></li>
-<li><strong>Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted. False is returned if both return NotImplemented.</strong></li>
+<li><strong>If eq() method is not overridden, it returns <code class="python hljs"><span class="hljs-string">'id(self) == id(other)'</span></code>, which is the same as <code class="python hljs"><span class="hljs-string">'self is other'</span></code>. That means all user-defined objects compare not equal by default (because id() returns object's memory address that is guaranteed to be unique).</strong></li>
+<li><strong>Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted. Result is False if both return NotImplemented.</strong></li>
 <li><strong>Ne() automatically works on any object that has eq() defined.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyComparable</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
@@ -934,9 +942,8 @@
 
 
 <div><h3 id="hashable">Hashable</h3><ul>
-<li><strong>Hashable object needs both hash() and eq() methods and its hash value should never change.</strong></li>
-<li><strong>Hashable objects that compare equal must have the same hash value, meaning default hash() that returns <code class="python hljs"><span class="hljs-string">'id(self)'</span></code> will not do.</strong></li>
-<li><strong>That is why Python automatically makes classes unhashable if you only implement eq().</strong></li>
+<li><strong>Hashable object needs both hash() and eq() methods and its hash value must not change.</strong></li>
+<li><strong>Hashable objects that compare equal must have the same hash value, meaning default hash() that returns <code class="python hljs"><span class="hljs-string">'id(self)'</span></code> will not do. That is why Python automatically makes classes unhashable if you only implement eq().</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyHashable</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
         self._a = a
@@ -953,7 +960,7 @@
 
 
 <div><h3 id="sortable">Sortable</h3><ul>
-<li><strong>With 'total_ordering' decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods and the rest will be automatically generated.</strong></li>
+<li><strong>With 'total_ordering' decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods (used by &lt;, &gt;, &lt;=, &gt;=) and the rest will be automatically generated.</strong></li>
 <li><strong>Functions sorted() and min() only require lt() method, while max() only requires gt(). However, it is best to define them all so that confusion doesn't arise in other contexts.</strong></li>
 <li><strong>When two lists, strings or dataclasses are compared, their values get compared in order until a pair of unequal values is found. The comparison of this two values is then returned. The shorter sequence is considered smaller in case of all values being equal.</strong></li>
 <li><strong>To sort collection of strings in proper alphabetical order pass <code class="python hljs"><span class="hljs-string">'key=locale.strxfrm'</span></code> to sorted() after running <code class="python hljs"><span class="hljs-string">'locale.setlocale(locale.LC_COLLATE, "en_US.UTF-8")'</span></code>.</strong></li>
@@ -977,7 +984,8 @@
 <div><h3 id="iterator-1">Iterator</h3><ul>
 <li><strong>Any object that has methods next() and iter() is an iterator.</strong></li>
 <li><strong>Next() should return next item or raise StopIteration exception.</strong></li>
-<li><strong>Iter() should return 'self'.</strong></li>
+<li><strong>Iter() should return an iterator of remaining items, i.e. 'self'.</strong></li>
+<li><strong>Any object that has iter() method can be used in a for loop.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Counter</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
         self.i = <span class="hljs-number">0</span>
@@ -994,13 +1002,13 @@
 (<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
 </code></pre>
 <div><h4 id="pythonhasmanydifferentiteratorobjects">Python has many different iterator objects:</h4><ul>
-<li><strong>Sequence iterators returned by the <a href="#iterator">iter()</a> function, such as list_iterator and set_iterator.</strong></li>
+<li><strong>Sequence iterators returned by the <a href="#iterator">iter()</a> function, such as list_iterator, etc.</strong></li>
 <li><strong>Objects returned by the <a href="#itertools">itertools</a> module, such as count, repeat and cycle.</strong></li>
 <li><strong>Generators returned by the <a href="#generator">generator functions</a> and <a href="#comprehensions">generator expressions</a>.</strong></li>
 <li><strong>File objects returned by the <a href="#open">open()</a> function, etc.</strong></li>
 </ul><div><h3 id="callable">Callable</h3><ul>
-<li><strong>All functions and classes have a call() method, hence are callable.</strong></li>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'callable(&lt;obj&gt;)'</span></code> or <code class="python hljs"><span class="hljs-string">'isinstance(&lt;obj&gt;, collections.abc.Callable)'</span></code> to check if object is callable.</strong></li>
+<li><strong>All functions and classes have a call() method that is executed when they are called.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'callable(&lt;obj&gt;)'</span></code> or <code class="python hljs"><span class="hljs-string">'isinstance(&lt;obj&gt;, collections.abc.Callable)'</span></code> to check if object is callable. You can also call the object and check if it raised TypeError.</strong></li>
 <li><strong>When this cheatsheet uses <code class="python hljs"><span class="hljs-string">'&lt;function&gt;'</span></code> as an argument, it means <code class="python hljs"><span class="hljs-string">'&lt;callable&gt;'</span></code>.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Counter</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
@@ -1019,8 +1027,8 @@
 </code></pre>
 <div><h3 id="contextmanager">Context Manager</h3><ul>
 <li><strong>With statements only work on objects that have enter() and exit() special methods.</strong></li>
-<li><strong>Enter() should lock the resources and optionally return an object.</strong></li>
-<li><strong>Exit() should release the resources.</strong></li>
+<li><strong>Enter() should lock the resources and optionally return an object (file, lock, etc.).</strong></li>
+<li><strong>Exit() should release the resources (for example close a file, release a lock, etc.).</strong></li>
 <li><strong>Any exception that happens inside the with block is passed to the exit() method.</strong></li>
 <li><strong>The exit() method can suppress the exception by returning a true value.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyOpen</span>:</span>
@@ -1062,7 +1070,7 @@
 </code></pre>
 <div><h3 id="collection">Collection</h3><ul>
 <li><strong>Only required methods are iter() and len(). Len() should return the number of items.</strong></li>
-<li><strong>This cheatsheet actually means <code class="python hljs"><span class="hljs-string">'&lt;iterable&gt;'</span></code> when it uses <code class="python hljs"><span class="hljs-string">'&lt;collection&gt;'</span></code>.</strong></li>
+<li><strong>This cheatsheet actually means <code class="python hljs"><span class="hljs-string">'&lt;iterable&gt;'</span></code> when it uses the <code class="python hljs"><span class="hljs-string">'&lt;collection&gt;'</span></code>.</strong></li>
 <li><strong>I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'. The main drawback of this decision is that the reader could think a certain function doesn't accept iterators when it does, since iterators are the only built-in objects that are iterable but are not collections.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyCollection</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
@@ -1077,8 +1085,7 @@
 
 
 <div><h3 id="sequence">Sequence</h3><ul>
-<li><strong>Only required methods are getitem() and len().</strong></li>
-<li><strong>Getitem() should return an item at the passed index or raise IndexError.</strong></li>
+<li><strong>Only required methods are getitem() and len(). Getitem() should return the item at the passed index or raise IndexError (it may also support negative indices and/or slices).</strong></li>
 <li><strong>Iter() and contains() automatically work on any object that has getitem() defined.</strong></li>
 <li><strong>Reversed() automatically works on any object that has getitem() and len() defined. It returns reversed iterator of object's items.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MySequence</span>:</span>
@@ -1098,16 +1105,16 @@
 
 
 <div><h4 id="discrepanciesbetweenglossarydefinitionsandabstractbaseclasses">Discrepancies between glossary definitions and abstract base classes:</h4><ul>
-<li><strong>Glossary on Python's website defines iterable as any object with iter() or getitem() and sequence as any object with getitem() and len(). It does not define collection.</strong></li>
-<li><strong>Passing ABC Iterable to isinstance() or issubclass() checks whether object/class has method iter(), while ABC Collection checks for iter(), contains() and len().</strong></li>
+<li><strong>Python's glossary defines iterable as any object with special methods iter() and/or getitem() and sequence as any object with getitem() and len(). It doesn't define collection.</strong></li>
+<li><strong>Passing ABC Iterable to isinstance() or issubclass() only checks whether object/class has special method iter(), while ABC Collection checks for iter(), contains() and len().</strong></li>
 </ul></div>
 
 
 
 
 <div><h3 id="abcsequence">ABC Sequence</h3><ul>
-<li><strong>It's a richer interface than the basic sequence.</strong></li>
-<li><strong>Extending it generates iter(), contains(), reversed(), index() and count().</strong></li>
+<li><strong>It's a richer interface than the basic sequence that also requires just getitem() and len().</strong></li>
+<li><strong>Extending it generates iter(), contains(), reversed(), index() and count() special methods.</strong></li>
 <li><strong>Unlike <code class="python hljs"><span class="hljs-string">'abc.Iterable'</span></code> and <code class="python hljs"><span class="hljs-string">'abc.Collection'</span></code>, it is not a duck type. That is why <code class="python hljs"><span class="hljs-string">'issubclass(MySequence, abc.Sequence)'</span></code> would return False even if MySequence had all the methods defined. It however recognizes list, tuple, range, str, bytes, bytearray, array, memoryview and deque, since they are registered as Sequence's virtual subclasses.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> abc
 
@@ -1141,8 +1148,8 @@
 
 <pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">enum_name</span>&gt;<span class="hljs-params">(Enum)</span>:</span>
     &lt;member_name&gt; = auto()              <span class="hljs-comment"># Increment of the last numeric value or 1.</span>
-    &lt;member_name&gt; = &lt;value&gt;             <span class="hljs-comment"># Values don't have to be hashable.</span>
-    &lt;member_name&gt; = &lt;el_1&gt;, &lt;el_2&gt;      <span class="hljs-comment"># Values can be collections (this is a tuple).</span>
+    &lt;member_name&gt; = &lt;value&gt;             <span class="hljs-comment"># Values don't have to be hashable or unique.</span>
+    &lt;member_name&gt; = &lt;el_1&gt;, &lt;el_2&gt;      <span class="hljs-comment"># Values can be collections. This is a tuple.</span>
 </code></pre>
 <ul>
 <li><strong>Methods receive the member they were called on as the 'self' argument.</strong></li>
@@ -1151,16 +1158,16 @@
 <pre><code class="python language-python hljs">&lt;member&gt; = &lt;enum&gt;.&lt;member_name&gt;         <span class="hljs-comment"># Returns a member. Raises AttributeError.</span>
 &lt;member&gt; = &lt;enum&gt;[<span class="hljs-string">'&lt;member_name&gt;'</span>]      <span class="hljs-comment"># Returns a member. Raises KeyError.</span>
 &lt;member&gt; = &lt;enum&gt;(&lt;value&gt;)              <span class="hljs-comment"># Returns a member. Raises ValueError.</span>
-&lt;str&gt;    = &lt;member&gt;.name                <span class="hljs-comment"># Returns member's name.</span>
-&lt;obj&gt;    = &lt;member&gt;.value               <span class="hljs-comment"># Returns member's value.</span>
+&lt;str&gt;    = &lt;member&gt;.name                <span class="hljs-comment"># Returns the member's name.</span>
+&lt;obj&gt;    = &lt;member&gt;.value               <span class="hljs-comment"># Returns the member's value.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;list&gt;   = list(&lt;enum&gt;)                 <span class="hljs-comment"># Returns enum's members.</span>
-&lt;list&gt;   = [a.name <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> &lt;enum&gt;]     <span class="hljs-comment"># Returns enum's member names.</span>
-&lt;list&gt;   = [a.value <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> &lt;enum&gt;]    <span class="hljs-comment"># Returns enum's member values.</span>
+<pre><code class="python language-python hljs">&lt;list&gt;   = list(&lt;enum&gt;)                 <span class="hljs-comment"># Returns a list of enum's members.</span>
+&lt;list&gt;   = &lt;enum&gt;._member_names_        <span class="hljs-comment"># Returns a list of member names.</span>
+&lt;list&gt;   = [m.value <span class="hljs-keyword">for</span> m <span class="hljs-keyword">in</span> &lt;enum&gt;]    <span class="hljs-comment"># Returns a list of member values.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;enum&gt;   = type(&lt;member&gt;)               <span class="hljs-comment"># Returns member's enum.</span>
-&lt;iter&gt;   = itertools.cycle(&lt;enum&gt;)      <span class="hljs-comment"># Returns endless iterator of members.</span>
-&lt;member&gt; = random.choice(list(&lt;enum&gt;))  <span class="hljs-comment"># Returns a random member.</span>
+<pre><code class="python language-python hljs">&lt;enum&gt;   = type(&lt;member&gt;)               <span class="hljs-comment"># Returns an enum. Also &lt;memb&gt;.__class__.</span>
+&lt;iter&gt;   = itertools.cycle(&lt;enum&gt;)      <span class="hljs-comment"># Returns an endless iterator of members.</span>
+&lt;member&gt; = random.choice(list(&lt;enum&gt;))  <span class="hljs-comment"># Randomly selects one of the members.</span>
 </code></pre>
 <div><h3 id="inline-1">Inline</h3><pre><code class="python language-python hljs">Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, <span class="hljs-string">'FORK KNIFE SPOON'</span>)
 Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, [<span class="hljs-string">'FORK'</span>, <span class="hljs-string">'KNIFE'</span>, <span class="hljs-string">'SPOON'</span>])
@@ -1193,8 +1200,8 @@
 <ul>
 <li><strong>Code inside the <code class="python hljs"><span class="hljs-string">'else'</span></code> block will only be executed if <code class="python hljs"><span class="hljs-string">'try'</span></code> block had no exceptions.</strong></li>
 <li><strong>Code inside the <code class="python hljs"><span class="hljs-string">'finally'</span></code> block will always be executed (unless a signal is received).</strong></li>
-<li><strong>All variables that are initialized in executed blocks are also visible in all subsequent blocks, as well as outside the try statement (only function block delimits scope).</strong></li>
-<li><strong>To catch signals use <code class="python hljs"><span class="hljs-string">'signal.signal(signal_number, &lt;func&gt;)'</span></code>.</strong></li>
+<li><strong>All variables that are initialized in executed blocks are also visible in all subsequent blocks, as well as outside the try statement (only the function block delimits scope).</strong></li>
+<li><strong>To catch signals use <code class="python hljs"><span class="hljs-string">'signal.signal(signal_number, handler_function)'</span></code>.</strong></li>
 </ul>
 <div><h3 id="catchingexceptions">Catching Exceptions</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">except</span> &lt;exception&gt;: ...
 <span class="hljs-keyword">except</span> &lt;exception&gt; <span class="hljs-keyword">as</span> &lt;name&gt;: ...
@@ -1203,10 +1210,10 @@
 </code></pre></div>
 
 <ul>
-<li><strong>Also catches subclasses of the exception.</strong></li>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'traceback.print_exc()'</span></code> to print the full error message to stderr.</strong></li>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'print(&lt;name&gt;)'</span></code> to print just the cause of the exception (its arguments).</strong></li>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'logging.exception(&lt;str&gt;)'</span></code> to log the passed message, followed by the full error message of the caught exception. For details see <a href="#logging">logging</a>.</strong></li>
+<li><strong>Also catches subclasses, e.g. <code class="python hljs"><span class="hljs-string">'IndexError'</span></code> is caught by <code class="python hljs"><span class="hljs-string">'except LookupError:'</span></code>.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'traceback.print_exc()'</span></code> to print the full error message to standard error stream.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'print(&lt;name&gt;)'</span></code> to print just the cause of the exception (that is, its arguments).</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'logging.exception(&lt;str&gt;)'</span></code> to log the passed message, followed by the full error message of the caught exception. For details about setting up the logger see <a href="#logging">Logging</a>.</strong></li>
 <li><strong>Use <code class="python hljs"><span class="hljs-string">'sys.exc_info()'</span></code> to get exception type, object, and traceback of caught exception.</strong></li>
 </ul>
 <div><h3 id="raisingexceptions">Raising Exceptions</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">raise</span> &lt;exception&gt;
@@ -1223,31 +1230,31 @@
 exc_type  = &lt;name&gt;.__class__
 filename  = &lt;name&gt;.__traceback__.tb_frame.f_code.co_filename
 func_name = &lt;name&gt;.__traceback__.tb_frame.f_code.co_name
-line      = linecache.getline(filename, &lt;name&gt;.__traceback__.tb_lineno)
+line_str  = linecache.getline(filename, &lt;name&gt;.__traceback__.tb_lineno)
 trace_str = <span class="hljs-string">''</span>.join(traceback.format_tb(&lt;name&gt;.__traceback__))
 error_msg = <span class="hljs-string">''</span>.join(traceback.format_exception(type(&lt;name&gt;), &lt;name&gt;, &lt;name&gt;.__traceback__))
 </code></pre></div>
 
 <div><h3 id="builtinexceptions">Built-in Exceptions</h3><pre><code class="text language-text">BaseException
- ├── SystemExit                   <span class="hljs-comment"># Raised by the sys.exit() function.</span>
- ├── KeyboardInterrupt            <span class="hljs-comment"># Raised when the user hits the interrupt key (ctrl-c).</span>
+ ├── SystemExit                   <span class="hljs-comment"># Raised by the sys.exit() function (see #Exit for details).</span>
+ ├── KeyboardInterrupt            <span class="hljs-comment"># Raised when the user hits the interrupt key (control-c).</span>
  └── Exception                    <span class="hljs-comment"># User-defined exceptions should be derived from this class.</span>
       ├── ArithmeticError         <span class="hljs-comment"># Base class for arithmetic errors such as ZeroDivisionError.</span>
       ├── AssertionError          <span class="hljs-comment"># Raised by `assert &lt;exp&gt;` if expression returns false value.</span>
       ├── AttributeError          <span class="hljs-comment"># Raised when object doesn't have requested attribute/method.</span>
       ├── EOFError                <span class="hljs-comment"># Raised by input() when it hits an end-of-file condition.</span>
       ├── LookupError             <span class="hljs-comment"># Base class for errors when a collection can't find an item.</span>
-      │    ├── IndexError         <span class="hljs-comment"># Raised when a sequence index is out of range.</span>
+      │    ├── IndexError         <span class="hljs-comment"># Raised when index of a sequence (list/str) is out of range.</span>
       │    └── KeyError           <span class="hljs-comment"># Raised when a dictionary key or set element is missing.</span>
       ├── MemoryError             <span class="hljs-comment"># Out of memory. May be too late to start deleting variables.</span>
       ├── NameError               <span class="hljs-comment"># Raised when nonexistent name (variable/func/class) is used.</span>
       │    └── UnboundLocalError  <span class="hljs-comment"># Raised when local name is used before it's being defined.</span>
-      ├── OSError                 <span class="hljs-comment"># Errors such as FileExistsError/TimeoutError (see #Open).</span>
-      │    └── ConnectionError    <span class="hljs-comment"># Errors such as BrokenPipeError/ConnectionAbortedError.</span>
+      ├── OSError                 <span class="hljs-comment"># Errors such as FileExistsError, TimeoutError (see #Open).</span>
+      │    └── ConnectionError    <span class="hljs-comment"># Errors such as BrokenPipeError and ConnectionAbortedError.</span>
       ├── RuntimeError            <span class="hljs-comment"># Raised by errors that don't fall into other categories.</span>
       │    ├── NotImplementedEr…  <span class="hljs-comment"># Can be raised by abstract methods or by unfinished code.</span>
-      │    └── RecursionError     <span class="hljs-comment"># Raised when the maximum recursion depth is exceeded.</span>
-      ├── StopIteration           <span class="hljs-comment"># Raised when an empty iterator is passed to next().</span>
+      │    └── RecursionError     <span class="hljs-comment"># Raised if max recursion depth is exceeded (3k by default).</span>
+      ├── StopIteration           <span class="hljs-comment"># Raised when exhausted (empty) iterator is passed to next().</span>
       ├── TypeError               <span class="hljs-comment"># When an argument of the wrong type is passed to function.</span>
       └── ValueError              <span class="hljs-comment"># When argument has the right type but inappropriate value.</span>
 </code></pre></div>
@@ -1282,7 +1289,7 @@
 </code></pre></div>
 
 <ul>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'file=sys.stderr'</span></code> for messages about errors.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'file=sys.stderr'</span></code> for messages about errors so they can be processed separately.</strong></li>
 <li><strong>Stdout and stderr streams hold output in a buffer until they receive a string containing '\n' or '\r', buffer reaches 4096 characters, <code class="python hljs"><span class="hljs-string">'flush=True'</span></code> is used, or program exits.</strong></li>
 </ul>
 <div><h3 id="prettyprint">Pretty Print</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> pprint <span class="hljs-keyword">import</span> pprint
@@ -1293,13 +1300,13 @@
 <li><strong>Each item is printed on its own line if collection exceeds 'width' characters.</strong></li>
 <li><strong>Nested collections that are 'depth' levels deep get printed as '…'.</strong></li>
 </ul>
-<div><h2 id="input"><a href="#input" name="input">#</a>Input</h2><pre><code class="python language-python hljs">&lt;str&gt; = input(prompt=<span class="hljs-keyword">None</span>)
+<div><h2 id="input"><a href="#input" name="input">#</a>Input</h2><pre><code class="python language-python hljs">&lt;str&gt; = input()
 </code></pre></div>
 
 <ul>
 <li><strong>Reads a line from the user input or pipe if present (trailing newline gets stripped).</strong></li>
-<li><strong>Prompt string is printed to the standard output before input is read.</strong></li>
-<li><strong>Raises EOFError when user hits EOF (ctrl-d/ctrl-z⏎) or input stream gets exhausted.</strong></li>
+<li><strong>If argument is passed, it gets printed to the standard output before input is read.</strong></li>
+<li><strong>EOFError is raised if user hits EOF (ctrl-d/ctrl-z⏎) or if stream is already exhausted.</strong></li>
 </ul>
 <div><h2 id="commandlinearguments"><a href="#commandlinearguments" name="commandlinearguments">#</a>Command Line Arguments</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> sys
 scripts_path = sys.argv[<span class="hljs-number">0</span>]
@@ -1307,7 +1314,7 @@
 </code></pre></div>
 
 <div><h3 id="argumentparser">Argument Parser</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> argparse <span class="hljs-keyword">import</span> ArgumentParser, FileType
-p = ArgumentParser(description=&lt;str&gt;)                             <span class="hljs-comment"># Returns a parser.</span>
+p = ArgumentParser(description=&lt;str&gt;)                             <span class="hljs-comment"># Returns a parser object.</span>
 p.add_argument(<span class="hljs-string">'-&lt;short_name&gt;'</span>, <span class="hljs-string">'--&lt;name&gt;'</span>, action=<span class="hljs-string">'store_true'</span>)  <span class="hljs-comment"># Flag (defaults to False).</span>
 p.add_argument(<span class="hljs-string">'-&lt;short_name&gt;'</span>, <span class="hljs-string">'--&lt;name&gt;'</span>, type=&lt;type&gt;)          <span class="hljs-comment"># Option (defaults to None).</span>
 p.add_argument(<span class="hljs-string">'&lt;name&gt;'</span>, type=&lt;type&gt;, nargs=<span class="hljs-number">1</span>)                    <span class="hljs-comment"># Mandatory first argument.</span>
@@ -1319,15 +1326,15 @@
 
 <ul>
 <li><strong>Use <code class="python hljs"><span class="hljs-string">'help=&lt;str&gt;'</span></code> to set argument description that will be displayed in help message.</strong></li>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'default=&lt;obj&gt;'</span></code> to set option's or optional argument's default value.</strong></li>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'type=FileType(&lt;mode&gt;)'</span></code> for files. Accepts 'encoding', but 'newline' is None.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'default=&lt;obj&gt;'</span></code> to override None as option's or optional argument's default value.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'type=FileType(&lt;mode&gt;)'</span></code> for files. It accepts 'encoding', but 'newline' is None.</strong></li>
 </ul>
-<div><h2 id="open"><a href="#open" name="open">#</a>Open</h2><p><strong>Opens the file and returns a corresponding file object.</strong></p><pre><code class="python language-python hljs">&lt;file&gt; = open(&lt;path&gt;, mode=<span class="hljs-string">'r'</span>, encoding=<span class="hljs-keyword">None</span>, newline=<span class="hljs-keyword">None</span>)
+<div><h2 id="open"><a href="#open" name="open">#</a>Open</h2><p><strong>Opens a file and returns the corresponding file object.</strong></p><pre><code class="python language-python hljs">&lt;file&gt; = open(&lt;path&gt;, mode=<span class="hljs-string">'r'</span>, encoding=<span class="hljs-keyword">None</span>, newline=<span class="hljs-keyword">None</span>)
 </code></pre></div>
 
 
 <ul>
-<li><strong><code class="python hljs"><span class="hljs-string">'encoding=None'</span></code> means that the default encoding is used, which is platform dependent. Best practice is to use <code class="python hljs"><span class="hljs-string">'encoding="utf-8"'</span></code> whenever possible.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'encoding=None'</span></code> means that the default encoding is used, which is platform dependent. Best practice is to use <code class="python hljs"><span class="hljs-string">'encoding="utf-8"'</span></code> until it becomes the default (Python 3.15).</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'newline=None'</span></code> means all different end of line combinations are converted to '\n' on read, while on write all '\n' characters are converted to system's default line separator.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'newline=""'</span></code> means no conversions take place, but input is still broken into chunks by readline() and readlines() on every '\n', '\r' and '\r\n'.</strong></li>
 </ul>
@@ -1339,15 +1346,15 @@
 <li><strong><code class="python hljs"><span class="hljs-string">'w+'</span></code> - Read and write. Deletes existing contents.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'r+'</span></code> - Read and write from the start.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'a+'</span></code> - Read and write from the end.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'b'</span></code>  - Binary mode (<code class="python hljs"><span class="hljs-string">'rb'</span></code>, <code class="python hljs"><span class="hljs-string">'wb'</span></code>, <code class="python hljs"><span class="hljs-string">'xb'</span></code>, …)</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'b'</span></code>  - Binary mode (<code class="python hljs"><span class="hljs-string">'rb'</span></code>, <code class="python hljs"><span class="hljs-string">'wb'</span></code>, <code class="python hljs"><span class="hljs-string">'xb'</span></code>, …).</strong></li>
 </ul><div><h3 id="exceptions-1">Exceptions</h3><ul>
 <li><strong><code class="python hljs"><span class="hljs-string">'FileNotFoundError'</span></code> can be raised when reading with <code class="python hljs"><span class="hljs-string">'r'</span></code> or <code class="python hljs"><span class="hljs-string">'r+'</span></code>.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'FileExistsError'</span></code> can be raised when writing with <code class="python hljs"><span class="hljs-string">'x'</span></code>.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'IsADirectoryError'</span></code> and <code class="python hljs"><span class="hljs-string">'PermissionError'</span></code> can be raised by any.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'OSError'</span></code> is the parent class of all listed exceptions.</strong></li>
-</ul><div><h3 id="fileobject">File Object</h3><pre><code class="python language-python hljs">&lt;file&gt;.seek(<span class="hljs-number">0</span>)                      <span class="hljs-comment"># Moves to the start of the file.</span>
+</ul><div><h3 id="fileobject">File Object</h3><pre><code class="python language-python hljs">&lt;file&gt;.seek(<span class="hljs-number">0</span>)                      <span class="hljs-comment"># Moves current position to the start of file.</span>
 &lt;file&gt;.seek(offset)                 <span class="hljs-comment"># Moves 'offset' chars/bytes from the start.</span>
-&lt;file&gt;.seek(<span class="hljs-number">0</span>, <span class="hljs-number">2</span>)                   <span class="hljs-comment"># Moves to the end of the file.</span>
+&lt;file&gt;.seek(<span class="hljs-number">0</span>, <span class="hljs-number">2</span>)                   <span class="hljs-comment"># Moves current position to the end of file.</span>
 &lt;bin_file&gt;.seek(±offset, origin)    <span class="hljs-comment"># Origin: 0 start, 1 current position, 2 end.</span>
 </code></pre></div></div></div>
 
@@ -1355,12 +1362,12 @@
 
 
 
-<pre><code class="python language-python hljs">&lt;str/bytes&gt; = &lt;file&gt;.read(size=<span class="hljs-number">-1</span>)  <span class="hljs-comment"># Reads 'size' chars/bytes or until EOF.</span>
+<pre><code class="python language-python hljs">&lt;str/bytes&gt; = &lt;file&gt;.read(size=<span class="hljs-number">-1</span>)  <span class="hljs-comment"># Reads 'size' chars/bytes or until the EOF.</span>
 &lt;str/bytes&gt; = &lt;file&gt;.readline()     <span class="hljs-comment"># Returns a line or empty string/bytes on EOF.</span>
-&lt;list&gt;      = &lt;file&gt;.readlines()    <span class="hljs-comment"># Returns a list of remaining lines.</span>
-&lt;str/bytes&gt; = next(&lt;file&gt;)          <span class="hljs-comment"># Returns a line using buffer. Do not mix.</span>
+&lt;list&gt;      = &lt;file&gt;.readlines()    <span class="hljs-comment"># Returns remaining lines. Also list(&lt;file&gt;).</span>
+&lt;str/bytes&gt; = next(&lt;file&gt;)          <span class="hljs-comment"># Returns a line using a read-ahead buffer.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;file&gt;.write(&lt;str/bytes&gt;)           <span class="hljs-comment"># Writes a string or bytes object.</span>
+<pre><code class="python language-python hljs">&lt;file&gt;.write(&lt;str/bytes&gt;)           <span class="hljs-comment"># Writes a str or bytes object to write buffer.</span>
 &lt;file&gt;.writelines(&lt;collection&gt;)     <span class="hljs-comment"># Writes a coll. of strings or bytes objects.</span>
 &lt;file&gt;.flush()                      <span class="hljs-comment"># Flushes write buffer. Runs every 4096/8192 B.</span>
 &lt;file&gt;.close()                      <span class="hljs-comment"># Closes the file after flushing write buffer.</span>
@@ -1383,27 +1390,27 @@
 </code></pre></div>
 
 <pre><code class="python language-python hljs">&lt;str&gt;  = os.getcwd()                <span class="hljs-comment"># Returns working dir. Starts as shell's $PWD.</span>
-&lt;str&gt;  = os.path.join(&lt;path&gt;, ...)  <span class="hljs-comment"># Joins two or more pathname components.</span>
+&lt;str&gt;  = os.path.join(&lt;path&gt;, ...)  <span class="hljs-comment"># Uses os.sep to join strings or Path objects.</span>
 &lt;str&gt;  = os.path.realpath(&lt;path&gt;)   <span class="hljs-comment"># Resolves symlinks and calls path.abspath().</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;str&gt;  = os.path.basename(&lt;path&gt;)   <span class="hljs-comment"># Returns final component of the path.</span>
 &lt;str&gt;  = os.path.dirname(&lt;path&gt;)    <span class="hljs-comment"># Returns path without the final component.</span>
 &lt;tup.&gt; = os.path.splitext(&lt;path&gt;)   <span class="hljs-comment"># Splits on last period of the final component.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;list&gt; = os.listdir(path=<span class="hljs-string">'.'</span>)       <span class="hljs-comment"># Returns filenames located at the path.</span>
+<pre><code class="python language-python hljs">&lt;list&gt; = os.listdir(path=<span class="hljs-string">'.'</span>)       <span class="hljs-comment"># Returns all filenames located at the path.</span>
 &lt;list&gt; = glob.glob(<span class="hljs-string">'&lt;pattern&gt;'</span>)     <span class="hljs-comment"># Returns paths matching the wildcard pattern.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;bool&gt; = os.path.exists(&lt;path&gt;)     <span class="hljs-comment"># Or: &lt;Path&gt;.exists()</span>
-&lt;bool&gt; = os.path.isfile(&lt;path&gt;)     <span class="hljs-comment"># Or: &lt;DirEntry/Path&gt;.is_file()</span>
-&lt;bool&gt; = os.path.isdir(&lt;path&gt;)      <span class="hljs-comment"># Or: &lt;DirEntry/Path&gt;.is_dir()</span>
+<pre><code class="python language-python hljs">&lt;bool&gt; = os.path.exists(&lt;path&gt;)     <span class="hljs-comment"># Checks if path exists. Also &lt;Path&gt;.exists().</span>
+&lt;bool&gt; = os.path.isfile(&lt;path&gt;)     <span class="hljs-comment"># Also &lt;Path&gt;.is_file() and &lt;DirEntry&gt;.is_file().</span>
+&lt;bool&gt; = os.path.isdir(&lt;path&gt;)      <span class="hljs-comment"># Also &lt;Path&gt;.is_dir() and &lt;DirEntry&gt;.is_dir().</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;stat&gt; = os.stat(&lt;path&gt;)            <span class="hljs-comment"># Or: &lt;DirEntry/Path&gt;.stat()</span>
-&lt;num&gt;  = &lt;stat&gt;.st_mtime/st_size/…  <span class="hljs-comment"># Modification time, size in bytes, ...</span>
+<pre><code class="python language-python hljs">&lt;stat&gt; = os.stat(&lt;path&gt;)            <span class="hljs-comment"># File's status. Also &lt;Path/DirEntry&gt;.stat().</span>
+&lt;num&gt;  = &lt;stat&gt;.st_mtime/st_size/…  <span class="hljs-comment"># Returns modification time, size in bytes, etc.</span>
 </code></pre>
 <div><h3 id="direntry">DirEntry</h3><p><strong>Unlike listdir(), scandir() returns DirEntry objects that cache isfile, isdir, and on Windows also stat information, thus significantly increasing the performance of code that requires it.</strong></p><pre><code class="python language-python hljs">&lt;iter&gt; = os.scandir(path=<span class="hljs-string">'.'</span>)       <span class="hljs-comment"># Returns DirEntry objects located at the path.</span>
-&lt;str&gt;  = &lt;DirEntry&gt;.path            <span class="hljs-comment"># Returns the whole path as a string.</span>
-&lt;str&gt;  = &lt;DirEntry&gt;.name            <span class="hljs-comment"># Returns final component as a string.</span>
-&lt;file&gt; = open(&lt;DirEntry&gt;)           <span class="hljs-comment"># Opens the file and returns a file object.</span>
+&lt;str&gt;  = &lt;DirEntry&gt;.path            <span class="hljs-comment"># Is absolute if 'path' argument was absolute.</span>
+&lt;str&gt;  = &lt;DirEntry&gt;.name            <span class="hljs-comment"># Returns path's final component as a string.</span>
+&lt;file&gt; = open(&lt;DirEntry&gt;)           <span class="hljs-comment"># Opens the file and returns its file object.</span>
 </code></pre></div>
 
 
@@ -1412,27 +1419,27 @@
 &lt;Path&gt; = &lt;Path&gt;.resolve()           <span class="hljs-comment"># Returns absolute path with resolved symlinks.</span>
 </code></pre></div>
 
-<pre><code class="python language-python hljs">&lt;Path&gt; = Path()                     <span class="hljs-comment"># Returns relative CWD. Also Path('.').</span>
+<pre><code class="python language-python hljs">&lt;Path&gt; = Path()                     <span class="hljs-comment"># Returns current working dir. Also Path('.').</span>
 &lt;Path&gt; = Path.cwd()                 <span class="hljs-comment"># Returns absolute CWD. Also Path().resolve().</span>
 &lt;Path&gt; = Path.home()                <span class="hljs-comment"># Returns user's home directory (absolute).</span>
-&lt;Path&gt; = Path(__file__).resolve()   <span class="hljs-comment"># Returns script's path if CWD wasn't changed.</span>
+&lt;Path&gt; = Path(__file__).resolve()   <span class="hljs-comment"># Returns module's path if CWD wasn't changed.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;Path&gt; = &lt;Path&gt;.parent              <span class="hljs-comment"># Returns Path without the final component.</span>
-&lt;str&gt;  = &lt;Path&gt;.name                <span class="hljs-comment"># Returns final component as a string.</span>
-&lt;str&gt;  = &lt;Path&gt;.stem                <span class="hljs-comment"># Returns final component without extension.</span>
-&lt;str&gt;  = &lt;Path&gt;.suffix              <span class="hljs-comment"># Returns final component's extension.</span>
-&lt;tup.&gt; = &lt;Path&gt;.parts               <span class="hljs-comment"># Returns all components as strings.</span>
+&lt;str&gt;  = &lt;Path&gt;.name                <span class="hljs-comment"># Returns path's final component as a string.</span>
+&lt;str&gt;  = &lt;Path&gt;.suffix              <span class="hljs-comment"># Returns name's last extension, e.g. '.gz'.</span>
+&lt;str&gt;  = &lt;Path&gt;.stem                <span class="hljs-comment"># Returns name without the last extension.</span>
+&lt;tup.&gt; = &lt;Path&gt;.parts               <span class="hljs-comment"># Returns all path's components as strings.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;iter&gt; = &lt;Path&gt;.iterdir()           <span class="hljs-comment"># Returns directory contents as Path objects.</span>
 &lt;iter&gt; = &lt;Path&gt;.glob(<span class="hljs-string">'&lt;pattern&gt;'</span>)   <span class="hljs-comment"># Returns Paths matching the wildcard pattern.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;str&gt;  = str(&lt;Path&gt;)                <span class="hljs-comment"># Returns path as a string.</span>
-&lt;file&gt; = open(&lt;Path&gt;)               <span class="hljs-comment"># Also &lt;Path&gt;.read/write_text/bytes(&lt;args&gt;).</span>
+<pre><code class="python language-python hljs">&lt;str&gt;  = str(&lt;Path&gt;)                <span class="hljs-comment"># Returns path as string. Also &lt;Path&gt;.as_uri().</span>
+&lt;file&gt; = open(&lt;Path&gt;)               <span class="hljs-comment"># Also &lt;Path&gt;.read_text/write_bytes(&lt;args&gt;).</span>
 </code></pre>
 <div><h2 id="oscommands"><a href="#oscommands" name="oscommands">#</a>OS Commands</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> os, shutil, subprocess
 </code></pre></div>
 
-<pre><code class="python language-python hljs">os.chdir(&lt;path&gt;)                    <span class="hljs-comment"># Changes the current working directory.</span>
+<pre><code class="python language-python hljs">os.chdir(&lt;path&gt;)                    <span class="hljs-comment"># Changes the current working directory (CWD).</span>
 os.mkdir(&lt;path&gt;, mode=<span class="hljs-number">0o777</span>)        <span class="hljs-comment"># Creates a directory. Permissions are in octal.</span>
 os.makedirs(&lt;path&gt;, mode=<span class="hljs-number">0o777</span>)     <span class="hljs-comment"># Creates all path's dirs. Also `exist_ok=False`.</span>
 </code></pre>
@@ -1440,24 +1447,24 @@
 shutil.copy2(from, to)              <span class="hljs-comment"># Also copies creation and modification time.</span>
 shutil.copytree(from, to)           <span class="hljs-comment"># Copies the directory. 'to' must not exist.</span>
 </code></pre>
-<pre><code class="python language-python hljs">os.rename(from, to)                 <span class="hljs-comment"># Renames/moves the file or directory.</span>
+<pre><code class="python language-python hljs">os.rename(from, to)                 <span class="hljs-comment"># Renames or moves the file or directory 'from'.</span>
 os.replace(from, to)                <span class="hljs-comment"># Same, but overwrites file 'to' even on Windows.</span>
 shutil.move(from, to)               <span class="hljs-comment"># Rename() that moves into 'to' if it's a dir.</span>
 </code></pre>
-<pre><code class="python language-python hljs">os.remove(&lt;path&gt;)                   <span class="hljs-comment"># Deletes the file.</span>
-os.rmdir(&lt;path&gt;)                    <span class="hljs-comment"># Deletes the empty directory.</span>
-shutil.rmtree(&lt;path&gt;)               <span class="hljs-comment"># Deletes the directory.</span>
+<pre><code class="python language-python hljs">os.remove(&lt;path&gt;)                   <span class="hljs-comment"># Deletes the file. Or `pip3 install send2trash`.</span>
+os.rmdir(&lt;path&gt;)                    <span class="hljs-comment"># Deletes the empty directory or raises OSError.</span>
+shutil.rmtree(&lt;path&gt;)               <span class="hljs-comment"># Deletes the directory and all of its contents.</span>
 </code></pre>
 <ul>
-<li><strong>Paths can be either strings, Paths, or DirEntry objects.</strong></li>
-<li><strong>Functions report OS related errors by raising either OSError or one of its <a href="#exceptions-1">subclasses</a>.</strong></li>
+<li><strong>Paths can be either strings, Path objects, or DirEntry objects.</strong></li>
+<li><strong>Functions report OS related errors by raising OSError or one of its <a href="#exceptions-1">subclasses</a>.</strong></li>
 </ul>
 <div><h3 id="shellcommands">Shell Commands</h3><pre><code class="python language-python hljs">&lt;pipe&gt; = os.popen(<span class="hljs-string">'&lt;commands&gt;'</span>)     <span class="hljs-comment"># Executes commands in sh/cmd. Returns combined stdout.</span>
 &lt;str&gt;  = &lt;pipe&gt;.read(size=<span class="hljs-number">-1</span>)       <span class="hljs-comment"># Reads 'size' chars or until EOF. Also readline/s().</span>
 &lt;int&gt;  = &lt;pipe&gt;.close()             <span class="hljs-comment"># Returns None if last command exited with returncode 0.</span>
 </code></pre></div>
 
-<div><h4 id="sends11tothebasiccalculatorandcapturesitsoutput">Sends '1 + 1' to the basic calculator and captures its output:</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>subprocess.run(<span class="hljs-string">'bc'</span>, input=<span class="hljs-string">'1 + 1\n'</span>, capture_output=<span class="hljs-keyword">True</span>, text=<span class="hljs-keyword">True</span>)
+<div><h4 id="sends11tothebasiccalculatorandcapturesitsoutput">Sends "1 + 1" to the basic calculator and captures its output:</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>subprocess.run(<span class="hljs-string">'bc'</span>, input=<span class="hljs-string">'1 + 1\n'</span>, capture_output=<span class="hljs-keyword">True</span>, text=<span class="hljs-keyword">True</span>)
 CompletedProcess(args=<span class="hljs-string">'bc'</span>, returncode=<span class="hljs-number">0</span>, stdout=<span class="hljs-string">'2\n'</span>, stderr=<span class="hljs-string">''</span>)
 </code></pre></div>
 
@@ -1470,19 +1477,19 @@
 </code></pre></div>
 
 <div><h2 id="json"><a href="#json" name="json">#</a>JSON</h2><p><strong>Text file format for storing collections of strings and numbers.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> json
-&lt;str&gt;    = json.dumps(&lt;object&gt;)     <span class="hljs-comment"># Converts object to JSON string.</span>
-&lt;object&gt; = json.loads(&lt;str&gt;)        <span class="hljs-comment"># Converts JSON string to object.</span>
+&lt;str&gt;  = json.dumps(&lt;list/dict&gt;)    <span class="hljs-comment"># Converts collection to JSON string.</span>
+&lt;coll&gt; = json.loads(&lt;str&gt;)          <span class="hljs-comment"># Converts JSON string to collection.</span>
 </code></pre></div>
 
 
-<div><h3 id="readobjectfromjsonfile">Read Object from JSON File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_json_file</span><span class="hljs-params">(filename)</span>:</span>
+<div><h3 id="readcollectionfromjsonfile">Read Collection from JSON File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_json_file</span><span class="hljs-params">(filename)</span>:</span>
     <span class="hljs-keyword">with</span> open(filename, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
         <span class="hljs-keyword">return</span> json.load(file)
 </code></pre></div>
 
-<div><h3 id="writeobjecttojsonfile">Write Object to JSON File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_json_file</span><span class="hljs-params">(filename, an_object)</span>:</span>
+<div><h3 id="writecollectiontojsonfile">Write Collection to JSON File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_json_file</span><span class="hljs-params">(filename, collection)</span>:</span>
     <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'w'</span>, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
-        json.dump(an_object, file, ensure_ascii=<span class="hljs-keyword">False</span>, indent=<span class="hljs-number">2</span>)
+        json.dump(collection, file, ensure_ascii=<span class="hljs-keyword">False</span>, indent=<span class="hljs-number">2</span>)
 </code></pre></div>
 
 <div><h2 id="pickle"><a href="#pickle" name="pickle">#</a>Pickle</h2><p><strong>Binary file format for storing Python objects.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> pickle
@@ -1491,12 +1498,12 @@
 </code></pre></div>
 
 
-<div><h3 id="readobjectfromfile">Read Object from File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_pickle_file</span><span class="hljs-params">(filename)</span>:</span>
+<div><h3 id="readobjectfrompicklefile">Read Object from Pickle File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_pickle_file</span><span class="hljs-params">(filename)</span>:</span>
     <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'rb'</span>) <span class="hljs-keyword">as</span> file:
         <span class="hljs-keyword">return</span> pickle.load(file)
 </code></pre></div>
 
-<div><h3 id="writeobjecttofile">Write Object to File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_pickle_file</span><span class="hljs-params">(filename, an_object)</span>:</span>
+<div><h3 id="writeobjecttopicklefile">Write Object to Pickle File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_pickle_file</span><span class="hljs-params">(filename, an_object)</span>:</span>
     <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'wb'</span>) <span class="hljs-keyword">as</span> file:
         pickle.dump(an_object, file)
 </code></pre></div>
@@ -1505,33 +1512,34 @@
 </code></pre></div>
 
 
-<div><h3 id="read">Read</h3><pre><code class="python language-python hljs">&lt;reader&gt; = csv.reader(&lt;file&gt;)       <span class="hljs-comment"># Also: `dialect='excel', delimiter=','`.</span>
-&lt;list&gt;   = next(&lt;reader&gt;)           <span class="hljs-comment"># Returns next row as a list of strings.</span>
-&lt;list&gt;   = list(&lt;reader&gt;)           <span class="hljs-comment"># Returns a list of remaining rows.</span>
-</code></pre></div>
-
+<pre><code class="python language-python hljs">&lt;file&gt;   = open(&lt;path&gt;, newline=<span class="hljs-string">''</span>)       <span class="hljs-comment"># Opens the CSV (text) file for reading.</span>
+&lt;reader&gt; = csv.reader(&lt;file&gt;)             <span class="hljs-comment"># Also: `dialect='excel', delimiter=','`.</span>
+&lt;list&gt;   = next(&lt;reader&gt;)                 <span class="hljs-comment"># Returns next row as a list of strings.</span>
+&lt;list&gt;   = list(&lt;reader&gt;)                 <span class="hljs-comment"># Returns a list of all remaining rows.</span>
+</code></pre>
 <ul>
-<li><strong>File must be opened with a <code class="python hljs"><span class="hljs-string">'newline=""'</span></code> argument, or newlines embedded inside quoted fields will not be interpreted correctly!</strong></li>
-<li><strong>To print the spreadsheet to the console use <a href="#table">Tabulate</a> library.</strong></li>
-<li><strong>For XML and binary Excel files (xlsx, xlsm and xlsb) use <a href="#dataframeplotencodedecode">Pandas</a> library.</strong></li>
-<li><strong>Reader accepts any iterator of strings, not just files.</strong></li>
+<li><strong>Without the <code class="python hljs"><span class="hljs-string">'newline=""'</span></code> argument, every '\r\n' sequence that is embedded inside a quoted field will get converted to '\n'! For details about newline argument see <a href="#open">Open</a>.</strong></li>
+<li><strong>To print the spreadsheet to the console use <a href="#table">Tabulate</a> or PrettyTable library.</strong></li>
+<li><strong>For XML and binary Excel files (xlsx, xlsm and xlsb) use <a href="#fileformats">Pandas</a> library.</strong></li>
+<li><strong>Reader accepts any iterator (or collection) of strings, not just files.</strong></li>
 </ul>
-<div><h3 id="write">Write</h3><pre><code class="python language-python hljs">&lt;writer&gt; = csv.writer(&lt;file&gt;)       <span class="hljs-comment"># Also: `dialect='excel', delimiter=','`.</span>
-&lt;writer&gt;.writerow(&lt;collection&gt;)     <span class="hljs-comment"># Encodes objects using `str(&lt;el&gt;)`.</span>
-&lt;writer&gt;.writerows(&lt;coll_of_coll&gt;)  <span class="hljs-comment"># Appends multiple rows.</span>
+<div><h3 id="write">Write</h3><pre><code class="python language-python hljs">&lt;file&gt;   = open(&lt;path&gt;, <span class="hljs-string">'w'</span>, newline=<span class="hljs-string">''</span>)  <span class="hljs-comment"># Opens the CSV (text) file for writing.</span>
+&lt;writer&gt; = csv.writer(&lt;file&gt;)             <span class="hljs-comment"># Also: `dialect='excel', delimiter=','`.</span>
+&lt;writer&gt;.writerow(&lt;collection&gt;)           <span class="hljs-comment"># Encodes each object using `str(&lt;el&gt;)`.</span>
+&lt;writer&gt;.writerows(&lt;coll_of_coll&gt;)        <span class="hljs-comment"># Appends multiple rows to the file.</span>
 </code></pre></div>
 
 <ul>
-<li><strong>File must be opened with a <code class="python hljs"><span class="hljs-string">'newline=""'</span></code> argument, or '\r' will be added in front of every '\n' on platforms that use '\r\n' line endings!</strong></li>
+<li><strong>If file is opened without the <code class="python hljs"><span class="hljs-string">'newline=""'</span></code> argument, '\r' will be added in front of every '\n' on platforms that use '\r\n' line endings (i.e., newlines may get doubled on Windows)!</strong></li>
 <li><strong>Open existing file with <code class="python hljs"><span class="hljs-string">'mode="a"'</span></code> to append to it or <code class="python hljs"><span class="hljs-string">'mode="w"'</span></code> to overwrite it.</strong></li>
 </ul>
 <div><h3 id="parameters">Parameters</h3><ul>
 <li><strong><code class="python hljs"><span class="hljs-string">'dialect'</span></code> - Master parameter that sets the default values. String or a 'csv.Dialect' object.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'delimiter'</span></code> - A one-character string used to separate fields.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'lineterminator'</span></code> - How writer terminates rows. Reader is hardcoded to '\n', '\r', '\r\n'.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'quotechar'</span></code> - Character for quoting fields that contain special characters.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'escapechar'</span></code> - Character for escaping quotechars.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'doublequote'</span></code> - Whether quotechars inside fields are/get doubled or escaped.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'delimiter'</span></code> - A one-character string that separates fields (comma, tab, semicolon, etc.).</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'lineterminator'</span></code> - How writer terminates rows. Reader looks for '\n', '\r' and '\r\n'.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'quotechar'</span></code> - Character for quoting fields containing delimiters, quotechars, '\n' or '\r'.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'escapechar'</span></code> - Character for escaping quotechars (not needed if doublequote is True).</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'doublequote'</span></code> - Whether quotechars inside fields are/get doubled instead of escaped.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'quoting'</span></code> - 0: As necessary, 1: All, 2: All but numbers which are read as floats, 3: None.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'skipinitialspace'</span></code> - Is space character at the start of the field stripped by the reader.</strong></li>
 </ul><div><h3 id="dialects">Dialects</h3><pre><code class="text language-text">┏━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┓
@@ -1560,49 +1568,49 @@
         writer.writerows(rows)
 </code></pre></div>
 
-<div><h2 id="sqlite"><a href="#sqlite" name="sqlite">#</a>SQLite</h2><p><strong>A server-less database engine that stores each database into a separate file.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> sqlite3
-&lt;conn&gt; = sqlite3.connect(&lt;path&gt;)                <span class="hljs-comment"># Opens existing or new file. Also ':memory:'.</span>
-&lt;conn&gt;.close()                                  <span class="hljs-comment"># Closes connection. Discards uncommitted data.</span>
+<div><h2 id="sqlite"><a href="#sqlite" name="sqlite">#</a>SQLite</h2><p><strong>A server-less database engine that stores each database into its own file.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> sqlite3
+&lt;conn&gt; = sqlite3.connect(&lt;path&gt;)               <span class="hljs-comment"># Opens existing or new file. Also ':memory:'.</span>
+&lt;conn&gt;.close()                                 <span class="hljs-comment"># Closes connection. Discards uncommitted data.</span>
 </code></pre></div>
 
 
-<div><h3 id="read-1">Read</h3><pre><code class="python language-python hljs">&lt;cursor&gt; = &lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)            <span class="hljs-comment"># Can raise a subclass of sqlite3.Error.</span>
-&lt;tuple&gt;  = &lt;cursor&gt;.fetchone()                  <span class="hljs-comment"># Returns next row. Also next(&lt;cursor&gt;).</span>
-&lt;list&gt;   = &lt;cursor&gt;.fetchall()                  <span class="hljs-comment"># Returns remaining rows. Also list(&lt;cursor&gt;).</span>
+<div><h3 id="read">Read</h3><pre><code class="python language-python hljs">&lt;cursor&gt; = &lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)           <span class="hljs-comment"># Can raise a subclass of sqlite3.Error.</span>
+&lt;tuple&gt;  = &lt;cursor&gt;.fetchone()                 <span class="hljs-comment"># Returns the next row. Also next(&lt;cursor&gt;).</span>
+&lt;list&gt;   = &lt;cursor&gt;.fetchall()                 <span class="hljs-comment"># Returns remaining rows. Also list(&lt;cursor&gt;).</span>
 </code></pre></div>
 
-<div><h3 id="write-1">Write</h3><pre><code class="python language-python hljs">&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)                       <span class="hljs-comment"># Can raise a subclass of sqlite3.Error.</span>
-&lt;conn&gt;.commit()                                 <span class="hljs-comment"># Saves all changes since the last commit.</span>
-&lt;conn&gt;.rollback()                               <span class="hljs-comment"># Discards all changes since the last commit.</span>
+<div><h3 id="write-1">Write</h3><pre><code class="python language-python hljs">&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)                      <span class="hljs-comment"># Can raise a subclass of sqlite3.Error.</span>
+&lt;conn&gt;.commit()                                <span class="hljs-comment"># Saves all changes since the last commit.</span>
+&lt;conn&gt;.rollback()                              <span class="hljs-comment"># Discards all changes since the last commit.</span>
 </code></pre></div>
 
-<div><h4 id="or">Or:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">with</span> &lt;conn&gt;:                                    <span class="hljs-comment"># Exits the block with commit() or rollback(),</span>
-    &lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)                   <span class="hljs-comment"># depending on whether any exception occurred.</span>
+<div><h4 id="or">Or:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">with</span> &lt;conn&gt;:                                   <span class="hljs-comment"># Exits the block with commit() or rollback(),</span>
+    &lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)                  <span class="hljs-comment"># depending on whether any exception occurred.</span>
 </code></pre></div>
 
-<div><h3 id="placeholders">Placeholders</h3><pre><code class="python language-python hljs">&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;list/tuple&gt;)         <span class="hljs-comment"># Replaces '?'s in query with values.</span>
-&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;dict/namedtuple&gt;)    <span class="hljs-comment"># Replaces ':&lt;key&gt;'s with values.</span>
-&lt;conn&gt;.executemany(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;coll_of_above&gt;)  <span class="hljs-comment"># Runs execute() multiple times.</span>
+<div><h3 id="placeholders">Placeholders</h3><pre><code class="python language-python hljs">&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;list/tuple&gt;)        <span class="hljs-comment"># Replaces every question mark with an item.</span>
+&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;dict/namedtuple&gt;)   <span class="hljs-comment"># Replaces every :&lt;key&gt; with a matching value.</span>
+&lt;conn&gt;.executemany(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;coll_of_coll&gt;)  <span class="hljs-comment"># Runs execute() once for each collection.</span>
 </code></pre></div>
 
 <ul>
-<li><strong>Passed values can be of type str, int, float, bytes, None or bool (stored as 1 or 0).</strong></li>
+<li><strong>Passed values can be of type str, int, float, bytes, None, or bool (stored as 1 or 0).</strong></li>
+<li><strong>SQLite does not restrict columns to any type unless table is declared as strict.</strong></li>
 </ul>
 <div><h3 id="example-1">Example</h3><p><strong>Values are not actually saved in this example because <code class="python hljs"><span class="hljs-string">'conn.commit()'</span></code> is omitted!</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>conn = sqlite3.connect(<span class="hljs-string">'test.db'</span>)
-<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'CREATE TABLE person (person_id INTEGER PRIMARY KEY, name, height)'</span>)
-<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'INSERT INTO person VALUES (NULL, ?, ?)'</span>, (<span class="hljs-string">'Jean-Luc'</span>, <span class="hljs-number">187</span>)).lastrowid
-<span class="hljs-number">1</span>
-<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'SELECT * FROM person'</span>).fetchall()
+<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'CREATE TABLE person (name TEXT, height INTEGER) STRICT'</span>)
+<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'INSERT INTO person VALUES (?, ?)'</span>, (<span class="hljs-string">'Jean-Luc'</span>, <span class="hljs-number">187</span>))
+<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'SELECT rowid, * FROM person'</span>).fetchall()
 [(<span class="hljs-number">1</span>, <span class="hljs-string">'Jean-Luc'</span>, <span class="hljs-number">187</span>)]
 </code></pre></div>
 
 
 <div><h3 id="sqlalchemy">SQLAlchemy</h3><p><strong>Library for interacting with various DB systems via SQL, method chaining, or ORM.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install sqlalchemy</span>
 <span class="hljs-keyword">from</span> sqlalchemy <span class="hljs-keyword">import</span> create_engine, text
-&lt;engine&gt; = create_engine(<span class="hljs-string">'&lt;url&gt;'</span>)               <span class="hljs-comment"># Url: 'dialect://user:password@host/dbname'.</span>
-&lt;conn&gt;   = &lt;engine&gt;.connect()                   <span class="hljs-comment"># Creates a connection. Also &lt;conn&gt;.close().</span>
-&lt;cursor&gt; = &lt;conn&gt;.execute(text(<span class="hljs-string">'&lt;query&gt;'</span>), …)   <span class="hljs-comment"># Replaces ':&lt;key&gt;'s with keyword arguments.</span>
-<span class="hljs-keyword">with</span> &lt;conn&gt;.begin(): ...                        <span class="hljs-comment"># Exits the block with commit or rollback.</span>
+&lt;engine&gt; = create_engine(<span class="hljs-string">'&lt;url&gt;'</span>)              <span class="hljs-comment"># Url: 'dialect://user:password@host/dbname'.</span>
+&lt;conn&gt;   = &lt;engine&gt;.connect()                  <span class="hljs-comment"># Creates a connection. Also &lt;conn&gt;.close().</span>
+&lt;cursor&gt; = &lt;conn&gt;.execute(text(<span class="hljs-string">'&lt;query&gt;'</span>), …)  <span class="hljs-comment"># `&lt;dict&gt;`. Replaces every :&lt;key&gt; with value.</span>
+<span class="hljs-keyword">with</span> &lt;conn&gt;.begin(): ...                       <span class="hljs-comment"># Exits the block with commit or rollback.</span>
 </code></pre></div>
 
 
@@ -1616,19 +1624,19 @@
 ┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
 </code></pre>
 <div><h2 id="bytes"><a href="#bytes" name="bytes">#</a>Bytes</h2><p><strong>A bytes object is an immutable sequence of single bytes. Mutable version is called bytearray.</strong></p><pre><code class="python language-python hljs">&lt;bytes&gt; = <span class="hljs-string">b'&lt;str&gt;'</span>                       <span class="hljs-comment"># Only accepts ASCII characters and \x00-\xff.</span>
-&lt;int&gt;   = &lt;bytes&gt;[index]                 <span class="hljs-comment"># Returns an int in range from 0 to 255.</span>
+&lt;int&gt;   = &lt;bytes&gt;[index]                 <span class="hljs-comment"># Returns an integer in range from 0 to 255.</span>
 &lt;bytes&gt; = &lt;bytes&gt;[&lt;slice&gt;]               <span class="hljs-comment"># Returns bytes even if it has only one element.</span>
-&lt;bytes&gt; = &lt;bytes&gt;.join(&lt;coll_of_bytes&gt;)  <span class="hljs-comment"># Joins elements using bytes as a separator.</span>
+&lt;bytes&gt; = &lt;bytes&gt;.join(&lt;coll_of_bytes&gt;)  <span class="hljs-comment"># Joins elements by using bytes as a separator.</span>
 </code></pre></div>
 
 
-<div><h3 id="encode-1">Encode</h3><pre><code class="python language-python hljs">&lt;bytes&gt; = bytes(&lt;coll_of_ints&gt;)          <span class="hljs-comment"># Ints must be in range from 0 to 255.</span>
+<div><h3 id="encode-1">Encode</h3><pre><code class="python language-python hljs">&lt;bytes&gt; = bytes(&lt;coll_of_ints&gt;)          <span class="hljs-comment"># Integers must be in range from 0 to 255.</span>
 &lt;bytes&gt; = bytes(&lt;str&gt;, <span class="hljs-string">'utf-8'</span>)          <span class="hljs-comment"># Encodes the string. Also &lt;str&gt;.encode().</span>
 &lt;bytes&gt; = bytes.fromhex(<span class="hljs-string">'&lt;hex&gt;'</span>)         <span class="hljs-comment"># Hex pairs can be separated by whitespaces.</span>
 &lt;bytes&gt; = &lt;int&gt;.to_bytes(n_bytes, …)     <span class="hljs-comment"># `byteorder='big/little', signed=False`.</span>
 </code></pre></div>
 
-<div><h3 id="decode-1">Decode</h3><pre><code class="python language-python hljs">&lt;list&gt;  = list(&lt;bytes&gt;)                  <span class="hljs-comment"># Returns ints in range from 0 to 255.</span>
+<div><h3 id="decode-1">Decode</h3><pre><code class="python language-python hljs">&lt;list&gt;  = list(&lt;bytes&gt;)                  <span class="hljs-comment"># Returns integers in range from 0 to 255.</span>
 &lt;str&gt;   = str(&lt;bytes&gt;, <span class="hljs-string">'utf-8'</span>)          <span class="hljs-comment"># Returns a string. Also &lt;bytes&gt;.decode().</span>
 &lt;str&gt;   = &lt;bytes&gt;.hex()                  <span class="hljs-comment"># Returns hex pairs. Accepts `sep=&lt;str&gt;`.</span>
 &lt;int&gt;   = int.from_bytes(&lt;bytes&gt;, …)     <span class="hljs-comment"># `byteorder='big/little', signed=False`.</span>
@@ -1649,7 +1657,7 @@
 <li><strong>System’s type sizes, byte order, and alignment rules are used by default.</strong></li>
 </ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> struct <span class="hljs-keyword">import</span> pack, unpack
 
-&lt;bytes&gt; = pack(<span class="hljs-string">'&lt;format&gt;'</span>, &lt;el_1&gt; [, ...])  <span class="hljs-comment"># Packs objects according to format string.</span>
+&lt;bytes&gt; = pack(<span class="hljs-string">'&lt;format&gt;'</span>, &lt;el_1&gt; [, ...])  <span class="hljs-comment"># Packs numbers according to format string.</span>
 &lt;tuple&gt; = unpack(<span class="hljs-string">'&lt;format&gt;'</span>, &lt;bytes&gt;)       <span class="hljs-comment"># Use iter_unpack() to get iterator of tuples.</span>
 </code></pre></div>
 
@@ -1684,20 +1692,20 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 
 
 
-<div><h2 id="array"><a href="#array" name="array">#</a>Array</h2><p><strong>List that can only hold numbers of a predefined type. Available types and their minimum sizes in bytes are listed above. Type sizes and byte order are always determined by the system, however bytes of each element can be reversed with byteswap() method.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> array <span class="hljs-keyword">import</span> array
+<div><h2 id="array"><a href="#array" name="array">#</a>Array</h2><p><strong>List that can only hold numbers of a predefined type. Available types and their minimum sizes in bytes are listed above. Type sizes and byte order are always determined by the system, however bytes of each element can be reversed (by calling the byteswap() method).</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> array <span class="hljs-keyword">import</span> array
 </code></pre></div>
 
 
-<pre><code class="python language-python hljs">&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;coll_of_nums&gt;)  <span class="hljs-comment"># Array from collection of numbers.</span>
-&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;bytes&gt;)         <span class="hljs-comment"># Copies bytes to array's memory.</span>
-&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;array&gt;)         <span class="hljs-comment"># Treats array as a sequence of numbers.</span>
-&lt;array&gt;.fromfile(&lt;file&gt;, n_items)              <span class="hljs-comment"># Appends items from the binary file.</span>
+<pre><code class="python language-python hljs">&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;coll_of_nums&gt;)  <span class="hljs-comment"># Creates an array from collection of numbers.</span>
+&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;bytes&gt;)         <span class="hljs-comment"># Writes passed bytes to the array's memory.</span>
+&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;array&gt;)         <span class="hljs-comment"># Treats passed array as a sequence of numbers.</span>
+&lt;array&gt;.fromfile(&lt;file&gt;, n_items)              <span class="hljs-comment"># Appends file contents to the array's memory.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;bytes&gt; = bytes(&lt;array&gt;)                       <span class="hljs-comment"># Returns a copy of array's memory.</span>
-&lt;file&gt;.write(&lt;array&gt;)                          <span class="hljs-comment"># Writes array's memory to binary file.</span>
+<pre><code class="python language-python hljs">&lt;bytes&gt; = bytes(&lt;array&gt;)                       <span class="hljs-comment"># Returns a copy of array's memory as bytes.</span>
+&lt;file&gt;.write(&lt;array&gt;)                          <span class="hljs-comment"># Writes array's memory to the binary file.</span>
 </code></pre>
 <div><h2 id="memoryview"><a href="#memoryview" name="memoryview">#</a>Memory View</h2><p><strong>A sequence object that points to the memory of another bytes-like object. Each element can reference a single or multiple consecutive bytes, depending on format. Order and number of elements can be changed with slicing.</strong></p><pre><code class="python language-python hljs">&lt;mview&gt; = memoryview(&lt;bytes/bytearray/array&gt;)  <span class="hljs-comment"># Immutable if bytes is passed, else mutable.</span>
-&lt;obj&gt;   = &lt;mview&gt;[index]                       <span class="hljs-comment"># Returns int or float. Bytes if format is 'c'.</span>
+&lt;obj&gt;   = &lt;mview&gt;[index]                       <span class="hljs-comment"># Returns ints/floats. Bytes if format is 'c'.</span>
 &lt;mview&gt; = &lt;mview&gt;[&lt;slice&gt;]                     <span class="hljs-comment"># Returns memoryview with rearranged elements.</span>
 &lt;mview&gt; = &lt;mview&gt;.cast(<span class="hljs-string">'&lt;typecode&gt;'</span>)           <span class="hljs-comment"># Only works between B/b/c and other types.</span>
 &lt;mview&gt;.release()                              <span class="hljs-comment"># Releases memory buffer of the base object.</span>
@@ -1710,94 +1718,42 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 &lt;file&gt;.write(&lt;mview&gt;)                          <span class="hljs-comment"># Writes `bytes(&lt;mview&gt;)` to the binary file.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;list&gt;  = list(&lt;mview&gt;)                        <span class="hljs-comment"># Returns a list of ints, floats or bytes.</span>
-&lt;str&gt;   = str(&lt;mview&gt;, <span class="hljs-string">'utf-8'</span>)                <span class="hljs-comment"># Treats memoryview as a bytes object.</span>
+&lt;str&gt;   = str(&lt;mview&gt;, <span class="hljs-string">'utf-8'</span>)                <span class="hljs-comment"># Treats passed memoryview as a bytes object.</span>
 &lt;str&gt;   = &lt;mview&gt;.hex()                        <span class="hljs-comment"># Returns hex pairs. Accepts `sep=&lt;str&gt;`.</span>
 </code></pre>
-<div><h2 id="deque"><a href="#deque" name="deque">#</a>Deque</h2><p><strong>A thread-safe list with efficient appends and pops from either side. Pronounced "deck".</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> deque
+<div><h2 id="deque"><a href="#deque" name="deque">#</a>Deque</h2><p><strong>List with efficient appends and pops from either side.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> deque
 </code></pre></div>
 
 
 <pre><code class="python language-python hljs">&lt;deque&gt; = deque(&lt;collection&gt;)                  <span class="hljs-comment"># Use `maxlen=&lt;int&gt;` to set size limit.</span>
 &lt;deque&gt;.appendleft(&lt;el&gt;)                       <span class="hljs-comment"># Opposite element is dropped if full.</span>
-&lt;deque&gt;.extendleft(&lt;collection&gt;)               <span class="hljs-comment"># Passed collection gets reversed.</span>
-&lt;deque&gt;.rotate(n=<span class="hljs-number">1</span>)                            <span class="hljs-comment"># Last element becomes first.</span>
+&lt;deque&gt;.extendleft(&lt;collection&gt;)               <span class="hljs-comment"># Prepends reversed coll. to the deque.</span>
+&lt;deque&gt;.rotate(n=<span class="hljs-number">1</span>)                            <span class="hljs-comment"># Last element becomes the first one.</span>
 &lt;el&gt; = &lt;deque&gt;.popleft()                       <span class="hljs-comment"># Raises IndexError if deque is empty.</span>
 </code></pre>
-<div><h2 id="threading"><a href="#threading" name="threading">#</a>Threading</h2><p><strong>CPython interpreter can only run a single thread at a time. Using multiple threads won't result in a faster execution, unless at least one of the threads contains an I/O operation.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> threading <span class="hljs-keyword">import</span> Thread, Lock, RLock, Semaphore, Event, Barrier
-<span class="hljs-keyword">from</span> concurrent.futures <span class="hljs-keyword">import</span> ThreadPoolExecutor, as_completed
-</code></pre></div>
-
-
-<div><h3 id="thread">Thread</h3><pre><code class="python language-python hljs">&lt;Thread&gt; = Thread(target=&lt;function&gt;)           <span class="hljs-comment"># Use `args=&lt;collection&gt;` to set the arguments.</span>
-&lt;Thread&gt;.start()                               <span class="hljs-comment"># Starts the thread. Also &lt;Thread&gt;.is_alive().</span>
-&lt;Thread&gt;.join()                                <span class="hljs-comment"># Waits for the thread to finish.</span>
-</code></pre></div>
-
-<ul>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'kwargs=&lt;dict&gt;'</span></code> to pass keyword arguments to the function.</strong></li>
-<li><strong>Use <code class="python hljs"><span class="hljs-string">'daemon=True'</span></code>, or the program will not be able to exit while the thread is alive.</strong></li>
-</ul>
-<div><h3 id="lock">Lock</h3><pre><code class="python language-python hljs">&lt;lock&gt; = Lock/RLock()                          <span class="hljs-comment"># RLock can only be released by acquirer.</span>
-&lt;lock&gt;.acquire()                               <span class="hljs-comment"># Waits for the lock to be available.</span>
-&lt;lock&gt;.release()                               <span class="hljs-comment"># Makes the lock available again.</span>
-</code></pre></div>
-
-<div><h4 id="or-1">Or:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">with</span> &lt;lock&gt;:                                   <span class="hljs-comment"># Enters the block by calling acquire() and</span>
-    ...                                        <span class="hljs-comment"># exits it with release(), even on error.</span>
-</code></pre></div>
-
-<div><h3 id="semaphoreeventbarrier">Semaphore, Event, Barrier</h3><pre><code class="python language-python hljs">&lt;Semaphore&gt; = Semaphore(value=<span class="hljs-number">1</span>)               <span class="hljs-comment"># Lock that can be acquired by 'value' threads.</span>
-&lt;Event&gt;     = Event()                          <span class="hljs-comment"># Method wait() blocks until set() is called.</span>
-&lt;Barrier&gt;   = Barrier(n_times)                 <span class="hljs-comment"># Wait() blocks until it's called n_times.</span>
-</code></pre></div>
-
-<div><h3 id="queue">Queue</h3><pre><code class="python language-python hljs">&lt;Queue&gt; = queue.Queue(maxsize=<span class="hljs-number">0</span>)               <span class="hljs-comment"># A thread-safe first-in-first-out queue.</span>
-&lt;Queue&gt;.put(&lt;el&gt;)                              <span class="hljs-comment"># Blocks until queue stops being full.</span>
-&lt;Queue&gt;.put_nowait(&lt;el&gt;)                       <span class="hljs-comment"># Raises queue.Full exception if full.</span>
-&lt;el&gt; = &lt;Queue&gt;.get()                           <span class="hljs-comment"># Blocks until queue stops being empty.</span>
-&lt;el&gt; = &lt;Queue&gt;.get_nowait()                    <span class="hljs-comment"># Raises queue.Empty exception if empty.</span>
-</code></pre></div>
-
-<div><h3 id="threadpoolexecutor">Thread Pool Executor</h3><pre><code class="python language-python hljs">&lt;Exec&gt; = ThreadPoolExecutor(max_workers=<span class="hljs-keyword">None</span>)  <span class="hljs-comment"># Or: `with ThreadPoolExecutor() as &lt;name&gt;: ...`</span>
-&lt;iter&gt; = &lt;Exec&gt;.map(&lt;func&gt;, &lt;args_1&gt;, ...)     <span class="hljs-comment"># Multithreaded and non-lazy map(). Keeps order.</span>
-&lt;Futr&gt; = &lt;Exec&gt;.submit(&lt;func&gt;, &lt;arg_1&gt;, ...)   <span class="hljs-comment"># Creates a thread and returns its Future obj.</span>
-&lt;Exec&gt;.shutdown()                              <span class="hljs-comment"># Blocks until all threads finish executing.</span>
-</code></pre></div>
-
-<pre><code class="python language-python hljs">&lt;bool&gt; = &lt;Future&gt;.done()                       <span class="hljs-comment"># Checks if the thread has finished executing.</span>
-&lt;obj&gt;  = &lt;Future&gt;.result(timeout=<span class="hljs-keyword">None</span>)         <span class="hljs-comment"># Waits for thread to finish and returns result.</span>
-&lt;bool&gt; = &lt;Future&gt;.cancel()                     <span class="hljs-comment"># Cancels or returns False if running/finished.</span>
-&lt;iter&gt; = as_completed(&lt;coll_of_Futures&gt;)       <span class="hljs-comment"># `next(&lt;iter&gt;)` returns next completed Future.</span>
-</code></pre>
-<ul>
-<li><strong>Map() and as_completed() also accept 'timeout'. It causes futures.TimeoutError when next() is called/blocking. Map() times from original call and as_completed() from first call to next(). As_completed() fails if next() is called too late, even if all threads are done.</strong></li>
-<li><strong>Exceptions that happen inside threads are raised when map iterator's next() or Future's result() are called. Future's exception() method returns exception object or None.</strong></li>
-<li><strong>ProcessPoolExecutor provides true parallelism but: everything sent to/from workers must be <a href="#pickle">pickable</a>, queues must be sent using executor's 'initargs' and 'initializer' parameters, and executor should only be reachable via <code class="python hljs"><span class="hljs-string">'if __name__ == "__main__": ...'</span></code>.</strong></li>
-</ul>
-<div><h2 id="operator"><a href="#operator" name="operator">#</a>Operator</h2><p><strong>Module of functions that provide the functionality of operators. Functions are ordered by operator precedence, starting with least binding.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> operator <span class="hljs-keyword">as</span> op
+<div><h2 id="operator"><a href="#operator" name="operator">#</a>Operator</h2><p><strong>Module of functions that provide the functionality of operators. Functions are grouped by operator precedence, from least to most binding. Functions and operators in first, third and fifth line are also ordered by precedence within a group.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> operator <span class="hljs-keyword">as</span> op
 </code></pre></div>
 
 
 <pre><code class="python language-python hljs">&lt;bool&gt; = op.not_(&lt;obj&gt;)                                        <span class="hljs-comment"># or, and, not (or/and missing)</span>
 &lt;bool&gt; = op.eq/ne/lt/ge/is_/is_not/contains(&lt;obj&gt;, &lt;obj&gt;)      <span class="hljs-comment"># ==, !=, &lt;, &gt;=, is, is not, in</span>
-&lt;obj&gt;  = op.or_/xor/and_(&lt;int/set&gt;, &lt;int/set&gt;)                 <span class="hljs-comment"># |, ^, &amp;</span>
-&lt;int&gt;  = op.lshift/rshift(&lt;int&gt;, &lt;int&gt;)                        <span class="hljs-comment"># &lt;&lt;, &gt;&gt;</span>
-&lt;obj&gt;  = op.add/sub/mul/truediv/floordiv/mod(&lt;obj&gt;, &lt;obj&gt;)     <span class="hljs-comment"># +, -, *, /, //, %</span>
-&lt;num&gt;  = op.neg/invert(&lt;num&gt;)                                  <span class="hljs-comment"># -, ~</span>
-&lt;num&gt;  = op.pow(&lt;num&gt;, &lt;num&gt;)                                  <span class="hljs-comment"># **</span>
+&lt;obj&gt;  = op.or_/xor/and_(&lt;int/set&gt;, &lt;int/set&gt;)                 <span class="hljs-comment"># |, ^, &amp; (sorted by precedence)</span>
+&lt;int&gt;  = op.lshift/rshift(&lt;int&gt;, &lt;int&gt;)                        <span class="hljs-comment"># &lt;&lt;, &gt;&gt; (i.e. &lt;int&gt; &lt;&lt; n_bits)</span>
+&lt;obj&gt;  = op.add/sub/mul/truediv/floordiv/mod(&lt;obj&gt;, &lt;obj&gt;)     <span class="hljs-comment"># +, -, *, /, //, % (two groups)</span>
+&lt;num&gt;  = op.neg/invert(&lt;num&gt;)                                  <span class="hljs-comment"># -, ~ (negate and bitwise not)</span>
+&lt;num&gt;  = op.pow(&lt;num&gt;, &lt;num&gt;)                                  <span class="hljs-comment"># ** (pow() accepts 3 arguments)</span>
 &lt;func&gt; = op.itemgetter/attrgetter/methodcaller(&lt;obj&gt; [, ...])  <span class="hljs-comment"># [index/key], .name, .name([…])</span>
 </code></pre>
 <pre><code class="python language-python hljs">elementwise_sum  = map(op.add, list_a, list_b)
-sorted_by_second = sorted(&lt;coll.&gt;, key=op.itemgetter(<span class="hljs-number">1</span>))
-sorted_by_both   = sorted(&lt;coll.&gt;, key=op.itemgetter(<span class="hljs-number">1</span>, <span class="hljs-number">0</span>))
-product_of_elems = functools.reduce(op.mul, &lt;collection&gt;)
+sorted_by_second = sorted(&lt;coll&gt;, key=op.itemgetter(<span class="hljs-number">1</span>))
+sorted_by_both   = sorted(&lt;coll&gt;, key=op.itemgetter(<span class="hljs-number">1</span>, <span class="hljs-number">0</span>))
 first_element    = op.methodcaller(<span class="hljs-string">'pop'</span>, <span class="hljs-number">0</span>)(&lt;list&gt;)
 </code></pre>
 <ul>
 <li><strong>Most operators call the object's special method that is named after them (second object is passed as an argument), while logical operators call their own code that relies on bool().</strong></li>
 <li><strong>Comparisons can be chained: <code class="python hljs"><span class="hljs-string">'x &lt; y &lt; z'</span></code> gets converted to <code class="python hljs"><span class="hljs-string">'(x &lt; y) and (y &lt; z)</span></code>'.</strong></li>
 </ul>
-<div><h2 id="matchstatement"><a href="#matchstatement" name="matchstatement">#</a>Match Statement</h2><p><strong>Executes the first block with matching pattern. Added in Python 3.10.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">match</span> &lt;object/expression&gt;:
+<div><h2 id="matchstatement"><a href="#matchstatement" name="matchstatement">#</a>Match Statement</h2><p><strong>Executes the first block with matching pattern.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">match</span> &lt;object/expression&gt;:
     <span class="hljs-keyword">case</span> &lt;pattern&gt; [<span class="hljs-keyword">if</span> &lt;condition&gt;]:
         &lt;code&gt;
     ...
@@ -1809,19 +1765,18 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 &lt;wildcard_patt&gt; = _                                <span class="hljs-comment"># Matches any object. Useful in last case.</span>
 &lt;capture_patt&gt;  = &lt;name&gt;                           <span class="hljs-comment"># Matches any object and binds it to name.</span>
 &lt;as_pattern&gt;    = &lt;pattern&gt; <span class="hljs-keyword">as</span> &lt;name&gt;              <span class="hljs-comment"># Binds match to name. Also &lt;type&gt;(&lt;name&gt;).</span>
-&lt;or_pattern&gt;    = &lt;pattern&gt; | &lt;pattern&gt; [| ...]    <span class="hljs-comment"># Matches any of the patterns.</span>
-&lt;sequence_patt&gt; = [&lt;pattern&gt;, ...]                 <span class="hljs-comment"># Matches sequence with matching items.</span>
-&lt;mapping_patt&gt;  = {&lt;value_pattern&gt;: &lt;patt&gt;, ...}   <span class="hljs-comment"># Matches dictionary with matching items.</span>
-&lt;class_pattern&gt; = &lt;type&gt;(&lt;attr_name&gt;=&lt;patt&gt;, ...)  <span class="hljs-comment"># Matches object with matching attributes.</span>
+&lt;or_pattern&gt;    = &lt;pattern&gt; | &lt;pattern&gt; [| ...]    <span class="hljs-comment"># Matches if any of listed patterns match.</span>
+&lt;sequence_patt&gt; = [&lt;pattern&gt;, ...]                 <span class="hljs-comment"># Matches a sequence. All items must match.</span>
+&lt;mapping_patt&gt;  = {&lt;value_pattern&gt;: &lt;patt&gt;, ...}   <span class="hljs-comment"># Matches a dict that has matching items.</span>
+&lt;class_pattern&gt; = &lt;type&gt;(&lt;attr_name&gt;=&lt;patt&gt;, ...)  <span class="hljs-comment"># Matches an object if attributes match.</span>
 </code></pre></div>
 
 <ul>
-<li><strong>Sequence pattern can also be written as a tuple.</strong></li>
+<li><strong>Sequence pattern can also be written as a tuple, either with or without the brackets.</strong></li>
 <li><strong>Use <code class="python hljs"><span class="hljs-string">'*&lt;name&gt;'</span></code> and <code class="python hljs"><span class="hljs-string">'**&lt;name&gt;'</span></code> in sequence/mapping patterns to bind remaining items.</strong></li>
 <li><strong>Sequence pattern must match all items of the collection, while mapping pattern does not.</strong></li>
-<li><strong>Patterns can be surrounded with brackets to override precedence (<code class="python hljs"><span class="hljs-string">'|'</span></code> &gt; <code class="python hljs"><span class="hljs-string">'as'</span></code> &gt; <code class="python hljs"><span class="hljs-string">','</span></code>).</strong></li>
-<li><strong>Built-in types allow a single positional pattern that is matched against the entire object.</strong></li>
-<li><strong>All names that are bound in the matching case, as well as variables initialized in its block, are visible after the match statement.</strong></li>
+<li><strong>Patterns can be surrounded with brackets to override their precedence: <code class="python hljs"><span class="hljs-string">'|'</span></code> &gt; <code class="python hljs"><span class="hljs-string">'as'</span></code> &gt; <code class="python hljs"><span class="hljs-string">','</span></code>. For example, <code class="python hljs"><span class="hljs-string">'[1, 2]'</span></code> is matched by the <code class="python hljs"><span class="hljs-string">'case 1|2, 2|3 as x if x == 2:'</span></code> block.</strong></li>
+<li><strong>All names that are bound in the matching case, as well as variables initialized in its body, are visible after the match statement (only function block delimits scope).</strong></li>
 </ul>
 <div><h3 id="example-2">Example</h3><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> pathlib <span class="hljs-keyword">import</span> Path
 <span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">match</span> Path(<span class="hljs-string">'/home/gto/python-cheatsheet/README.md'</span>):
@@ -1829,16 +1784,16 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 <span class="hljs-meta">... </span>        parts=[<span class="hljs-string">'/'</span>, <span class="hljs-string">'home'</span>, user, *_]
 <span class="hljs-meta">... </span>    ) <span class="hljs-keyword">as</span> p <span class="hljs-keyword">if</span> p.name.lower().startswith(<span class="hljs-string">'readme'</span>) <span class="hljs-keyword">and</span> p.is_file():
 <span class="hljs-meta">... </span>        print(<span class="hljs-string">f'<span class="hljs-subst">{p.name}</span> is a readme file that belongs to user <span class="hljs-subst">{user}</span>.'</span>)
-<span class="hljs-string">'README.md is a readme file that belongs to user gto.'</span>
+README.md is a readme file that belongs to user gto.
 </code></pre></div>
 
 <div><h2 id="logging"><a href="#logging" name="logging">#</a>Logging</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> logging <span class="hljs-keyword">as</span> log
 </code></pre></div>
 
 <pre><code class="python language-python hljs">log.basicConfig(filename=&lt;path&gt;, level=<span class="hljs-string">'DEBUG'</span>)   <span class="hljs-comment"># Configures the root logger (see Setup).</span>
-log.debug/info/warning/error/critical(&lt;str&gt;)      <span class="hljs-comment"># Sends message to the root logger.</span>
-&lt;Logger&gt; = log.getLogger(__name__)                <span class="hljs-comment"># Returns logger named after the module.</span>
-&lt;Logger&gt;.&lt;level&gt;(&lt;str&gt;)                           <span class="hljs-comment"># Sends message to the logger.</span>
+log.debug/info/warning/error/critical(&lt;str&gt;)      <span class="hljs-comment"># Sends passed message to the root logger.</span>
+&lt;Logger&gt; = log.getLogger(__name__)                <span class="hljs-comment"># Returns a logger named after the module.</span>
+&lt;Logger&gt;.&lt;level&gt;(&lt;str&gt;)                           <span class="hljs-comment"># Sends the message. Same levels as above.</span>
 &lt;Logger&gt;.exception(&lt;str&gt;)                         <span class="hljs-comment"># Error() that appends caught exception.</span>
 </code></pre>
 <div><h3 id="setup">Setup</h3><pre><code class="python language-python hljs">log.basicConfig(
@@ -1849,11 +1804,11 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 )
 </code></pre></div>
 
-<pre><code class="python language-python hljs">&lt;Formatter&gt; = log.Formatter(<span class="hljs-string">'&lt;format&gt;'</span>)           <span class="hljs-comment"># Creates a Formatter.</span>
-&lt;Handler&gt; = log.FileHandler(&lt;path&gt;, mode=<span class="hljs-string">'a'</span>)     <span class="hljs-comment"># Creates a Handler. Also `encoding=None`.</span>
-&lt;Handler&gt;.setFormatter(&lt;Formatter&gt;)               <span class="hljs-comment"># Adds Formatter to the Handler.</span>
-&lt;Handler&gt;.setLevel(&lt;int/str&gt;)                     <span class="hljs-comment"># Processes all messages by default.</span>
-&lt;Logger&gt;.addHandler(&lt;Handler&gt;)                    <span class="hljs-comment"># Adds Handler to the Logger.</span>
+<pre><code class="python language-python hljs">&lt;Formatter&gt; = log.Formatter(<span class="hljs-string">'&lt;format&gt;'</span>)           <span class="hljs-comment"># Formats messages according to format str.</span>
+&lt;Handler&gt; = log.FileHandler(&lt;path&gt;, mode=<span class="hljs-string">'a'</span>)     <span class="hljs-comment"># Appends to file. Also `encoding=None`.</span>
+&lt;Handler&gt;.setFormatter(&lt;Formatter&gt;)               <span class="hljs-comment"># Only outputs bare messages by default.</span>
+&lt;Handler&gt;.setLevel(&lt;int/str&gt;)                     <span class="hljs-comment"># Prints or saves every message by default.</span>
+&lt;Logger&gt;.addHandler(&lt;Handler&gt;)                    <span class="hljs-comment"># Logger can have more than one handler.</span>
 &lt;Logger&gt;.setLevel(&lt;int/str&gt;)                      <span class="hljs-comment"># What is sent to its/ancestors' handlers.</span>
 &lt;Logger&gt;.propagate = &lt;bool&gt;                       <span class="hljs-comment"># Cuts off ancestors' handlers if False.</span>
 </code></pre>
@@ -1877,23 +1832,74 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 2023-02-07 23:21:01,430 CRITICAL:my_module:Running out of disk space.
 </code></pre></div>
 
-<div><h2 id="introspection"><a href="#introspection" name="introspection">#</a>Introspection</h2><pre><code class="python language-python hljs">&lt;list&gt; = dir()                      <span class="hljs-comment"># List of of local names (including functions and classes).</span>
+<div><h2 id="introspection"><a href="#introspection" name="introspection">#</a>Introspection</h2><pre><code class="python language-python hljs">&lt;list&gt; = dir()                      <span class="hljs-comment"># Local names of variables, functions, classes and modules.</span>
 &lt;dict&gt; = vars()                     <span class="hljs-comment"># Dict of local names and their objects. Also locals().</span>
-&lt;dict&gt; = globals()                  <span class="hljs-comment"># Dict of global names (for instance '__builtin__' module).</span>
+&lt;dict&gt; = globals()                  <span class="hljs-comment"># Dict of global names and their objects, e.g. __builtin__.</span>
 </code></pre></div>
 
-<pre><code class="python language-python hljs">&lt;list&gt; = dir(&lt;obj&gt;)                 <span class="hljs-comment"># Returns names of all object's attributes (incl. methods).</span>
+<pre><code class="python language-python hljs">&lt;list&gt; = dir(&lt;obj&gt;)                 <span class="hljs-comment"># Returns names of object's attributes (including methods).</span>
 &lt;dict&gt; = vars(&lt;obj&gt;)                <span class="hljs-comment"># Returns dict of writable attributes. Also &lt;obj&gt;.__dict__.</span>
 &lt;bool&gt; = hasattr(&lt;obj&gt;, <span class="hljs-string">'&lt;name&gt;'</span>)   <span class="hljs-comment"># Checks if object possesses attribute with passed name.</span>
-value  = getattr(&lt;obj&gt;, <span class="hljs-string">'&lt;name&gt;'</span>)   <span class="hljs-comment"># Returns object's attribute or raises AttributeError.</span>
-setattr(&lt;obj&gt;, <span class="hljs-string">'&lt;name&gt;'</span>, value)     <span class="hljs-comment"># Sets attribute. Only works on objects with __dict__.</span>
+value  = getattr(&lt;obj&gt;, <span class="hljs-string">'&lt;name&gt;'</span>)   <span class="hljs-comment"># Returns the object's attribute or raises AttributeError.</span>
+setattr(&lt;obj&gt;, <span class="hljs-string">'&lt;name&gt;'</span>, value)     <span class="hljs-comment"># Sets attribute. Only works on objects with __dict__ attr.</span>
 delattr(&lt;obj&gt;, <span class="hljs-string">'&lt;name&gt;'</span>)            <span class="hljs-comment"># Deletes attribute from __dict__. Also `del &lt;obj&gt;.&lt;name&gt;`.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;Sig&gt;  = inspect.signature(&lt;func&gt;)  <span class="hljs-comment"># Returns function's Signature object. Can accept a class.</span>
+<pre><code class="python language-python hljs">&lt;Sig&gt;  = inspect.signature(&lt;func&gt;)  <span class="hljs-comment"># Returns Signature object of the passed function or class.</span>
 &lt;dict&gt; = &lt;Sig&gt;.parameters           <span class="hljs-comment"># Returns dict of Parameters. Also &lt;Sig&gt;.return_annotation.</span>
 &lt;memb&gt; = &lt;Param&gt;.kind               <span class="hljs-comment"># Returns ParameterKind member (Parameter.KEYWORD_ONLY, …).</span>
 &lt;type&gt; = &lt;Param&gt;.annotation         <span class="hljs-comment"># Returns Parameter.empty if missing. Also &lt;Param&gt;.default.</span>
 </code></pre>
+<div><h2 id="threading"><a href="#threading" name="threading">#</a>Threading</h2><p><strong>CPython interpreter can only run a single thread at a time. Using multiple threads won't result in a faster execution, unless at least one of the threads contains an I/O operation.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> threading <span class="hljs-keyword">import</span> Thread, Lock, RLock, Semaphore, Event, Barrier
+<span class="hljs-keyword">from</span> concurrent.futures <span class="hljs-keyword">import</span> ThreadPoolExecutor, as_completed
+</code></pre></div>
+
+
+<div><h3 id="thread">Thread</h3><pre><code class="python language-python hljs">&lt;Thread&gt; = Thread(target=&lt;function&gt;)           <span class="hljs-comment"># Use `args=&lt;collection&gt;` to set the arguments.</span>
+&lt;Thread&gt;.start()                               <span class="hljs-comment"># Starts the thread. Also &lt;Thread&gt;.is_alive().</span>
+&lt;Thread&gt;.join()                                <span class="hljs-comment"># Waits for the thread to finish executing.</span>
+</code></pre></div>
+
+<ul>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'kwargs=&lt;dict&gt;'</span></code> to pass keyword arguments to the function.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'daemon=True'</span></code>, or the program won't be able to exit while the thread is alive.</strong></li>
+</ul>
+<div><h3 id="lock">Lock</h3><pre><code class="python language-python hljs">&lt;lock&gt; = Lock/RLock()                          <span class="hljs-comment"># RLock can only be released by acquirer.</span>
+&lt;lock&gt;.acquire()                               <span class="hljs-comment"># Waits for the lock to be available.</span>
+&lt;lock&gt;.release()                               <span class="hljs-comment"># Makes the lock available again.</span>
+</code></pre></div>
+
+<div><h4 id="or-1">Or:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">with</span> &lt;lock&gt;:                                   <span class="hljs-comment"># Enters the block by calling acquire() and</span>
+    ...                                        <span class="hljs-comment"># exits it with release(), even on error.</span>
+</code></pre></div>
+
+<div><h3 id="semaphoreeventbarrier">Semaphore, Event, Barrier</h3><pre><code class="python language-python hljs">&lt;Semaphore&gt; = Semaphore(value=<span class="hljs-number">1</span>)               <span class="hljs-comment"># Lock that can be acquired by 'value' threads.</span>
+&lt;Event&gt;     = Event()                          <span class="hljs-comment"># Method wait() blocks until set() is called.</span>
+&lt;Barrier&gt;   = Barrier(n_times)                 <span class="hljs-comment"># Wait() blocks until it's called n times.</span>
+</code></pre></div>
+
+<div><h3 id="queue">Queue</h3><pre><code class="python language-python hljs">&lt;Queue&gt; = queue.Queue(maxsize=<span class="hljs-number">0</span>)               <span class="hljs-comment"># A thread-safe first-in-first-out queue.</span>
+&lt;Queue&gt;.put(&lt;el&gt;)                              <span class="hljs-comment"># Blocks until queue stops being full.</span>
+&lt;Queue&gt;.put_nowait(&lt;el&gt;)                       <span class="hljs-comment"># Raises queue.Full exception if full.</span>
+&lt;el&gt; = &lt;Queue&gt;.get()                           <span class="hljs-comment"># Blocks until queue stops being empty.</span>
+&lt;el&gt; = &lt;Queue&gt;.get_nowait()                    <span class="hljs-comment"># Raises queue.Empty exception if empty.</span>
+</code></pre></div>
+
+<div><h3 id="threadpoolexecutor">Thread Pool Executor</h3><pre><code class="python language-python hljs">&lt;Exec&gt; = ThreadPoolExecutor(max_workers=<span class="hljs-keyword">None</span>)  <span class="hljs-comment"># Also `with ThreadPoolExecutor() as &lt;name&gt;: …`.</span>
+&lt;iter&gt; = &lt;Exec&gt;.map(&lt;func&gt;, &lt;args_1&gt;, ...)     <span class="hljs-comment"># Multithreaded and non-lazy map(). Keeps order.</span>
+&lt;Futr&gt; = &lt;Exec&gt;.submit(&lt;func&gt;, &lt;arg_1&gt;, ...)   <span class="hljs-comment"># Creates a thread and returns its Future obj.</span>
+&lt;Exec&gt;.shutdown()                              <span class="hljs-comment"># Waits for all submitted threads to finish.</span>
+</code></pre></div>
+
+<pre><code class="python language-python hljs">&lt;bool&gt; = &lt;Future&gt;.done()                       <span class="hljs-comment"># Checks if the thread has finished executing.</span>
+&lt;obj&gt;  = &lt;Future&gt;.result(timeout=<span class="hljs-keyword">None</span>)         <span class="hljs-comment"># Waits for thread to finish and returns result.</span>
+&lt;bool&gt; = &lt;Future&gt;.cancel()                     <span class="hljs-comment"># Cancels or returns False if running/finished.</span>
+&lt;iter&gt; = as_completed(&lt;coll_of_Futures&gt;)       <span class="hljs-comment"># `next(&lt;iter&gt;)` returns next completed Future.</span>
+</code></pre>
+<ul>
+<li><strong>Map() and as_completed() also accept 'timeout'. It causes futures.TimeoutError when next() is called/blocking. Map() times from original call and as_completed() from first call to next(). As_completed() fails if next() is called too late, even if all threads are done.</strong></li>
+<li><strong>Exceptions that happen inside threads are raised when map iterator's next() or Future's result() are called. Future's exception() method returns an exception object or None.</strong></li>
+<li><strong>ProcessPoolExecutor provides true parallelism but: everything sent to/from workers must be <a href="#pickle">pickable</a>, queues must be sent using executor's 'initargs' and 'initializer' parameters, and executor should only be reachable via <code class="python hljs"><span class="hljs-string">'if __name__ == "__main__": ...'</span></code>.</strong></li>
+</ul>
 <div><h2 id="coroutines"><a href="#coroutines" name="coroutines">#</a>Coroutines</h2><ul>
 <li><strong>Coroutines have a lot in common with threads, but unlike threads, they only give up control when they call another coroutine and they don’t use as much memory.</strong></li>
 <li><strong>Coroutine definition starts with <code class="python hljs"><span class="hljs-string">'async'</span></code> and its call with <code class="python hljs"><span class="hljs-string">'await'</span></code>.</strong></li>
@@ -1902,25 +1908,25 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 </code></pre></div>
 
 
-<pre><code class="python language-python hljs">&lt;coro&gt; = &lt;async_function&gt;(&lt;args&gt;)         <span class="hljs-comment"># Creates a coroutine by calling async def function.</span>
-&lt;obj&gt;  = <span class="hljs-keyword">await</span> &lt;coroutine&gt;                <span class="hljs-comment"># Starts the coroutine and returns its result.</span>
-&lt;task&gt; = aio.create_task(&lt;coroutine&gt;)     <span class="hljs-comment"># Schedules the coroutine for execution.</span>
-&lt;obj&gt;  = <span class="hljs-keyword">await</span> &lt;task&gt;                     <span class="hljs-comment"># Returns coroutine's result. Also &lt;task&gt;.cancel().</span>
+<pre><code class="python language-python hljs">&lt;coro&gt; = &lt;async_function&gt;(&lt;args&gt;)          <span class="hljs-comment"># Creates a coroutine by calling async def function.</span>
+&lt;obj&gt;  = <span class="hljs-keyword">await</span> &lt;coroutine&gt;                 <span class="hljs-comment"># Starts the coroutine and waits for its result.</span>
+&lt;task&gt; = aio.create_task(&lt;coroutine&gt;)      <span class="hljs-comment"># Schedules it for execution. Always keep the task.</span>
+&lt;obj&gt;  = <span class="hljs-keyword">await</span> &lt;task&gt;                      <span class="hljs-comment"># Returns coroutine's result. Also &lt;task&gt;.cancel().</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;coro&gt; = aio.gather(&lt;coro/task&gt;, ...)     <span class="hljs-comment"># Schedules coros. Returns list of results on await.</span>
-&lt;coro&gt; = aio.wait(&lt;tasks&gt;, …)             <span class="hljs-comment"># `aio.ALL/FIRST_COMPLETED`. Returns (done, pending).</span>
-&lt;iter&gt; = aio.as_completed(&lt;coros/tasks&gt;)  <span class="hljs-comment"># Iterator of coros. All return next result on await.</span>
+<pre><code class="python language-python hljs">&lt;coro&gt; = aio.gather(&lt;coro/task&gt;, ...)      <span class="hljs-comment"># Schedules coros. Returns list of results on await.</span>
+&lt;coro&gt; = aio.wait(&lt;tasks&gt;, return_when=…)  <span class="hljs-comment"># `'ALL/FIRST_COMPLETED'`. Returns (done, pending).</span>
+&lt;iter&gt; = aio.as_completed(&lt;coros/tasks&gt;)   <span class="hljs-comment"># Iter of coros that return next result on await.</span>
 </code></pre>
 <div><h4 id="runsaterminalgamewhereyoucontrolanasteriskthatmustavoidnumbers">Runs a terminal game where you control an asterisk that must avoid numbers:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> asyncio, collections, curses, curses.textpad, enum, random
 
-P = collections.namedtuple(<span class="hljs-string">'P'</span>, <span class="hljs-string">'x y'</span>)    <span class="hljs-comment"># Position</span>
-D = enum.Enum(<span class="hljs-string">'D'</span>, <span class="hljs-string">'n e s w'</span>)             <span class="hljs-comment"># Direction</span>
-W, H = <span class="hljs-number">15</span>, <span class="hljs-number">7</span>                              <span class="hljs-comment"># Width, Height</span>
+P = collections.namedtuple(<span class="hljs-string">'P'</span>, <span class="hljs-string">'x y'</span>)     <span class="hljs-comment"># Position (x and y coordinates).</span>
+D = enum.Enum(<span class="hljs-string">'D'</span>, <span class="hljs-string">'n e s w'</span>)              <span class="hljs-comment"># Direction (north, east, etc.).</span>
+W, H = <span class="hljs-number">15</span>, <span class="hljs-number">7</span>                               <span class="hljs-comment"># Width and height constants.</span>
 
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">(screen)</span>:</span>
-    curses.curs_set(<span class="hljs-number">0</span>)                    <span class="hljs-comment"># Makes cursor invisible.</span>
-    screen.nodelay(<span class="hljs-keyword">True</span>)                  <span class="hljs-comment"># Makes getch() non-blocking.</span>
-    asyncio.run(main_coroutine(screen))   <span class="hljs-comment"># Starts running asyncio code.</span>
+    curses.curs_set(<span class="hljs-number">0</span>)                     <span class="hljs-comment"># Makes the cursor invisible.</span>
+    screen.nodelay(<span class="hljs-keyword">True</span>)                   <span class="hljs-comment"># Makes getch() non-blocking.</span>
+    asyncio.run(main_coroutine(screen))    <span class="hljs-comment"># Starts running asyncio code.</span>
 
 <span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main_coroutine</span><span class="hljs-params">(screen)</span>:</span>
     moves = asyncio.Queue()
@@ -1979,9 +1985,8 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 plt.plot/bar/scatter(x_data, y_data [, label=&lt;str&gt;])  <span class="hljs-comment"># Also plt.plot(y_data).</span>
 plt.legend()                                          <span class="hljs-comment"># Adds a legend.</span>
 plt.title/xlabel/ylabel(&lt;str&gt;)                        <span class="hljs-comment"># Adds a title or label.</span>
-plt.savefig(&lt;path&gt;)                                   <span class="hljs-comment"># Saves the figure.</span>
-plt.show()                                            <span class="hljs-comment"># Displays the figure.</span>
-plt.clf()                                             <span class="hljs-comment"># Clears the figure.</span>
+plt.show()                                            <span class="hljs-comment"># Also plt.savefig(&lt;path&gt;).</span>
+plt.clf()                                             <span class="hljs-comment"># Clears the plot.</span>
 </code></pre></div>
 
 <div><h2 id="table"><a href="#table" name="table">#</a>Table</h2><div><h4 id="printsacsvspreadsheettotheconsole">Prints a CSV spreadsheet to the console:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install tabulate</span>
@@ -1994,7 +1999,7 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 
 <div><h2 id="consoleapp"><a href="#consoleapp" name="consoleapp">#</a>Console App</h2><div><h4 id="runsabasicfileexplorerintheconsole">Runs a basic file explorer in the console:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install windows-curses</span>
 <span class="hljs-keyword">import</span> curses, os
-<span class="hljs-keyword">from</span> curses <span class="hljs-keyword">import</span> A_REVERSE, KEY_DOWN, KEY_UP, KEY_LEFT, KEY_RIGHT, KEY_ENTER
+<span class="hljs-keyword">from</span> curses <span class="hljs-keyword">import</span> A_REVERSE, KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT
 
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">(screen)</span>:</span>
     ch, first, selected, paths = <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, os.listdir()
@@ -2005,10 +2010,11 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
             color = A_REVERSE <span class="hljs-keyword">if</span> filename == paths[selected] <span class="hljs-keyword">else</span> <span class="hljs-number">0</span>
             screen.addnstr(y, <span class="hljs-number">0</span>, filename, width-<span class="hljs-number">1</span>, color)
         ch = screen.getch()
-        selected += (ch == KEY_DOWN) - (ch == KEY_UP)
-        selected = max(<span class="hljs-number">0</span>, min(len(paths)-<span class="hljs-number">1</span>, selected))
-        first += (selected &gt;= first + height) - (selected &lt; first)
-        <span class="hljs-keyword">if</span> ch <span class="hljs-keyword">in</span> [KEY_LEFT, KEY_RIGHT, KEY_ENTER, ord(<span class="hljs-string">'\n'</span>), ord(<span class="hljs-string">'\r'</span>)]:
+        selected -= (ch == KEY_UP) <span class="hljs-keyword">and</span> (selected &gt; <span class="hljs-number">0</span>)
+        selected += (ch == KEY_DOWN) <span class="hljs-keyword">and</span> (selected &lt; len(paths)-<span class="hljs-number">1</span>)
+        first -= (first &gt; selected)
+        first += (first &lt; selected-(height-<span class="hljs-number">1</span>))
+        <span class="hljs-keyword">if</span> ch <span class="hljs-keyword">in</span> [KEY_LEFT, KEY_RIGHT, ord(<span class="hljs-string">'\n'</span>)]:
             new_dir = <span class="hljs-string">'..'</span> <span class="hljs-keyword">if</span> ch == KEY_LEFT <span class="hljs-keyword">else</span> paths[selected]
             <span class="hljs-keyword">if</span> os.path.isdir(new_dir):
                 os.chdir(new_dir)
@@ -2022,9 +2028,9 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 <div><h2 id="guiapp"><a href="#guiapp" name="guiapp">#</a>GUI App</h2><div><h4 id="aweightconverterguiapplication">A weight converter GUI application:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install PySimpleGUI</span>
 <span class="hljs-keyword">import</span> PySimpleGUI <span class="hljs-keyword">as</span> sg
 
-text_box = sg.Input(default_text=<span class="hljs-string">'100'</span>, enable_events=<span class="hljs-keyword">True</span>, key=<span class="hljs-string">'-QUANTITY-'</span>)
-dropdown = sg.InputCombo([<span class="hljs-string">'g'</span>, <span class="hljs-string">'kg'</span>, <span class="hljs-string">'t'</span>], <span class="hljs-string">'kg'</span>, readonly=<span class="hljs-keyword">True</span>, enable_events=<span class="hljs-keyword">True</span>, k=<span class="hljs-string">'-UNIT-'</span>)
-label    = sg.Text(<span class="hljs-string">'100 kg is 220.462 lbs.'</span>, key=<span class="hljs-string">'-OUTPUT-'</span>)
+text_box = sg.Input(default_text=<span class="hljs-string">'100'</span>, enable_events=<span class="hljs-keyword">True</span>, key=<span class="hljs-string">'QUANTITY'</span>)
+dropdown = sg.InputCombo([<span class="hljs-string">'g'</span>, <span class="hljs-string">'kg'</span>, <span class="hljs-string">'t'</span>], <span class="hljs-string">'kg'</span>, readonly=<span class="hljs-keyword">True</span>, enable_events=<span class="hljs-keyword">True</span>, k=<span class="hljs-string">'UNIT'</span>)
+label    = sg.Text(<span class="hljs-string">'100 kg is 220.462 lbs.'</span>, key=<span class="hljs-string">'OUTPUT'</span>)
 button   = sg.Button(<span class="hljs-string">'Close'</span>)
 window   = sg.Window(<span class="hljs-string">'Weight Converter'</span>, [[text_box, dropdown], [label], [button]])
 
@@ -2033,13 +2039,13 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
     <span class="hljs-keyword">if</span> event <span class="hljs-keyword">in</span> [sg.WIN_CLOSED, <span class="hljs-string">'Close'</span>]:
         <span class="hljs-keyword">break</span>
     <span class="hljs-keyword">try</span>:
-        quantity = float(values[<span class="hljs-string">'-QUANTITY-'</span>])
+        quantity = float(values[<span class="hljs-string">'QUANTITY'</span>])
     <span class="hljs-keyword">except</span> ValueError:
         <span class="hljs-keyword">continue</span>
-    unit = values[<span class="hljs-string">'-UNIT-'</span>]
+    unit = values[<span class="hljs-string">'UNIT'</span>]
     factors = {<span class="hljs-string">'g'</span>: <span class="hljs-number">0.001</span>, <span class="hljs-string">'kg'</span>: <span class="hljs-number">1</span>, <span class="hljs-string">'t'</span>: <span class="hljs-number">1000</span>}
     lbs = quantity * factors[unit] / <span class="hljs-number">0.45359237</span>
-    window[<span class="hljs-string">'-OUTPUT-'</span>].update(value=<span class="hljs-string">f'<span class="hljs-subst">{quantity}</span> <span class="hljs-subst">{unit}</span> is <span class="hljs-subst">{lbs:g}</span> lbs.'</span>)
+    window[<span class="hljs-string">'OUTPUT'</span>].update(value=<span class="hljs-string">f'<span class="hljs-subst">{quantity}</span> <span class="hljs-subst">{unit}</span> is <span class="hljs-subst">{lbs:g}</span> lbs.'</span>)
 window.close()
 </code></pre></div></div>
 
@@ -2052,10 +2058,9 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 table      = document.find(<span class="hljs-string">'table'</span>, class_=<span class="hljs-string">'infobox vevent'</span>)
 python_url = table.find(<span class="hljs-string">'th'</span>, text=<span class="hljs-string">'Website'</span>).next_sibling.a[<span class="hljs-string">'href'</span>]
 logo_url   = table.find(<span class="hljs-string">'img'</span>)[<span class="hljs-string">'src'</span>]
-logo       = requests.get(<span class="hljs-string">f'https:<span class="hljs-subst">{logo_url}</span>'</span>).content
 filename   = os.path.basename(logo_url)
 <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'wb'</span>) <span class="hljs-keyword">as</span> file:
-    file.write(logo)
+    file.write(requests.get(<span class="hljs-string">f'https:<span class="hljs-subst">{logo_url}</span>'</span>).content)
 print(<span class="hljs-string">f'<span class="hljs-subst">{python_url}</span>, file://<span class="hljs-subst">{os.path.abspath(filename)}</span>'</span>)
 </code></pre></div></div>
 
@@ -2065,6 +2070,7 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 
 &lt;WebDrv&gt; = webdriver.Chrome/Firefox/Safari/Edge()     <span class="hljs-comment"># Opens a browser. Also &lt;WebDrv&gt;.quit().</span>
 &lt;WebDrv&gt;.get(<span class="hljs-string">'&lt;url&gt;'</span>)                                 <span class="hljs-comment"># Also &lt;WebDrv&gt;.implicitly_wait(seconds).</span>
+&lt;str&gt;  = &lt;WebDrv&gt;.page_source                         <span class="hljs-comment"># Returns HTML of fully rendered page.</span>
 &lt;El&gt;   = &lt;WebDrv/El&gt;.find_element(<span class="hljs-string">'css selector'</span>, …)  <span class="hljs-comment"># '&lt;tag&gt;#&lt;id&gt;.&lt;class&gt;[&lt;attr&gt;="&lt;val&gt;"]…'.</span>
 &lt;list&gt; = &lt;WebDrv/El&gt;.find_elements(<span class="hljs-string">'xpath'</span>, …)        <span class="hljs-comment"># '//&lt;tag&gt;[@&lt;attr&gt;="&lt;val&gt;"]…'. See XPath.</span>
 &lt;str&gt;  = &lt;El&gt;.get_attribute(&lt;str&gt;)                    <span class="hljs-comment"># Property if exists. Also &lt;El&gt;.text.</span>
@@ -2087,19 +2093,19 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 
 
 <pre><code class="python language-python hljs">app = fl.Flask(__name__)                   <span class="hljs-comment"># Returns the app object. Put at the top.</span>
-app.run(host=<span class="hljs-keyword">None</span>, port=<span class="hljs-keyword">None</span>, debug=<span class="hljs-keyword">None</span>)  <span class="hljs-comment"># Or: $ flask --app FILE run [--ARG[=VAL] …]</span>
+app.run(host=<span class="hljs-keyword">None</span>, port=<span class="hljs-keyword">None</span>, debug=<span class="hljs-keyword">None</span>)  <span class="hljs-comment"># Or: $ flask --app FILE run [--ARG[=VAL]]…</span>
 </code></pre>
 <ul>
 <li><strong>Starts the app at <code class="python hljs"><span class="hljs-string">'http://localhost:5000'</span></code>. Use <code class="python hljs"><span class="hljs-string">'host="0.0.0.0"'</span></code> to run externally.</strong></li>
 <li><strong>Install a WSGI server like <a href="https://flask.palletsprojects.com/en/latest/deploying/waitress/">Waitress</a> and a HTTP server such as <a href="https://flask.palletsprojects.com/en/latest/deploying/nginx/">Nginx</a> for better security.</strong></li>
 <li><strong>Debug mode restarts the app whenever script changes and displays errors in the browser.</strong></li>
 </ul>
-<div><h3 id="staticrequest">Static Request</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@app.route('/img/&lt;path:filename&gt;')</span>
+<div><h3 id="servingfiles">Serving Files</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@app.route('/img/&lt;path:filename&gt;')</span>
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">serve_file</span><span class="hljs-params">(filename)</span>:</span>
-    <span class="hljs-keyword">return</span> fl.send_from_directory(<span class="hljs-string">'dirname/'</span>, filename)
+    <span class="hljs-keyword">return</span> fl.send_from_directory(<span class="hljs-string">'DIRNAME'</span>, filename)
 </code></pre></div>
 
-<div><h3 id="dynamicrequest">Dynamic Request</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@app.route('/&lt;sport&gt;')</span>
+<div><h3 id="servinghtml">Serving HTML</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@app.route('/&lt;sport&gt;')</span>
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">serve_html</span><span class="hljs-params">(sport)</span>:</span>
     <span class="hljs-keyword">return</span> fl.render_template_string(<span class="hljs-string">'&lt;h1&gt;{{title}}&lt;/h1&gt;'</span>, title=sport)
 </code></pre></div>
@@ -2107,10 +2113,10 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 <ul>
 <li><strong><code class="python hljs"><span class="hljs-string">'fl.render_template(filename, &lt;kwargs&gt;)'</span></code> renders a file located in 'templates' dir.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'fl.abort(&lt;int&gt;)'</span></code> returns error code and <code class="python hljs"><span class="hljs-string">'return fl.redirect(&lt;url&gt;)'</span></code> redirects.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'fl.request.args[&lt;str&gt;]'</span></code> returns parameter from the query string (URL right of '?').</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'fl.request.args[&lt;str&gt;]'</span></code> returns parameter from query string (URL part right of '?').</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'fl.session[&lt;str&gt;] = &lt;obj&gt;'</span></code> stores session data. It requires secret key to be set at the startup with <code class="python hljs"><span class="hljs-string">'app.secret_key = &lt;str&gt;'</span></code>.</strong></li>
 </ul>
-<div><h3 id="restrequest">REST Request</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@app.post('/&lt;sport&gt;/odds')</span>
+<div><h3 id="servingjson">Serving JSON</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@app.post('/&lt;sport&gt;/odds')</span>
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">serve_json</span><span class="hljs-params">(sport)</span>:</span>
     team = fl.request.form[<span class="hljs-string">'team'</span>]
     <span class="hljs-keyword">return</span> {<span class="hljs-string">'team'</span>: team, <span class="hljs-string">'odds'</span>: [<span class="hljs-number">2.09</span>, <span class="hljs-number">3.74</span>, <span class="hljs-number">3.68</span>]}
@@ -2181,7 +2187,7 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 </code></pre>
 <pre><code class="python language-python hljs">&lt;view&gt;  = &lt;array&gt;.reshape(&lt;shape&gt;)                      <span class="hljs-comment"># Also `&lt;array&gt;.shape = &lt;shape&gt;`.</span>
 &lt;array&gt; = &lt;array&gt;.flatten()                             <span class="hljs-comment"># Also `&lt;view&gt; = &lt;array&gt;.ravel()`.</span>
-&lt;view&gt;  = &lt;array&gt;.transpose()                           <span class="hljs-comment"># Or: &lt;array&gt;.T</span>
+&lt;view&gt;  = &lt;array&gt;.transpose()                           <span class="hljs-comment"># Flips the table over its diagonal.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;array&gt; = np.copy/abs/sqrt/log/int64(&lt;array&gt;)           <span class="hljs-comment"># Returns new array of the same shape.</span>
 &lt;array&gt; = &lt;array&gt;.sum/max/mean/argmax/all(axis)         <span class="hljs-comment"># Aggregates specified dimension.</span>
@@ -2211,47 +2217,45 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 </code></pre>
 <ul>
 <li><strong><code class="python hljs"><span class="hljs-string">':'</span></code> returns a slice of all dimension's indices. Omitted dimensions default to <code class="python hljs"><span class="hljs-string">':'</span></code>.</strong></li>
-<li><strong>Indices should not be tuples because Python converts <code class="python hljs"><span class="hljs-string">'obj[i, j]'</span></code>  to <code class="python hljs"><span class="hljs-string">'obj[(i, j)]'</span></code>!</strong></li>
-<li><strong>Indexing with a slice and 1d array works the same as when using two slices (lines 4, 6, 7).</strong></li>
+<li><strong>Python converts <code class="python hljs"><span class="hljs-string">'obj[i, j]'</span></code> to <code class="python hljs"><span class="hljs-string">'obj[(i, j)]'</span></code>. This makes <code class="python hljs"><span class="hljs-string">'&lt;2d&gt;[row_i, col_i]'</span></code> and <code class="python hljs"><span class="hljs-string">'&lt;2d&gt;[row_indices]'</span></code> indistinguishable to NumPy if tuple of two indices is passed!</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'ix_([1, 2], [3, 4])'</span></code> returns <code class="python hljs"><span class="hljs-string">'[[1], [2]]'</span></code> and <code class="python hljs"><span class="hljs-string">'[[3, 4]]'</span></code>. Due to broadcasting rules, this is the same as using <code class="python hljs"><span class="hljs-string">'[[1, 1], [2, 2]]'</span></code> and <code class="python hljs"><span class="hljs-string">'[[3, 4], [3, 4]]'</span></code>.</strong></li>
 <li><strong>Any value that is broadcastable to the indexed shape can be assigned to the selection.</strong></li>
 </ul>
-<div><h3 id="broadcasting">Broadcasting</h3><p><strong>A set of rules by which NumPy functions operate on arrays of different shapes.</strong></p><pre><code class="python language-python hljs">left  = [ <span class="hljs-number">0.1</span> ,  <span class="hljs-number">0.6</span> ,  <span class="hljs-number">0.8</span> ]                           <span class="hljs-comment"># Shape: (3,)</span>
-right = [[<span class="hljs-number">0.1</span>], [<span class="hljs-number">0.6</span>], [<span class="hljs-number">0.8</span>]]                           <span class="hljs-comment"># Shape: (3, 1)</span>
-</code></pre></div>
-
-
-<div><h4 id="1ifarrayshapesdifferinlengthleftpadtheshortershapewithones">1. If array shapes differ in length, left-pad the shorter shape with ones:</h4><pre><code class="python language-python hljs">left  = [[<span class="hljs-number">0.1</span> ,  <span class="hljs-number">0.6</span> ,  <span class="hljs-number">0.8</span>]]                           <span class="hljs-comment"># Shape: (1, 3) &lt;- !</span>
-right = [[<span class="hljs-number">0.1</span>], [<span class="hljs-number">0.6</span>], [<span class="hljs-number">0.8</span>]]                           <span class="hljs-comment"># Shape: (3, 1)</span>
-</code></pre></div>
-
-<div><h4 id="2ifanydimensionsdifferinsizeexpandtheonesthathavesize1byduplicatingtheirelements">2. If any dimensions differ in size, expand the ones that have size 1 by duplicating their elements:</h4><pre><code class="python language-python hljs">left  = [[<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>],                             <span class="hljs-comment"># Shape: (3, 3) &lt;- !</span>
-         [<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>],
-         [<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>]]
-
-right = [[<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.1</span>,  <span class="hljs-number">0.1</span>],                             <span class="hljs-comment"># Shape: (3, 3) &lt;- !</span>
-         [<span class="hljs-number">0.6</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.6</span>],
-         [<span class="hljs-number">0.8</span>,  <span class="hljs-number">0.8</span>,  <span class="hljs-number">0.8</span>]]
-</code></pre></div>
-
-<div><h3 id="example-3">Example</h3><div><h4 id="foreachpointreturnsindexofitsnearestpoint010608121">For each point returns index of its nearest point (<code class="python hljs">[<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>] =&gt; [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">1</span>]</code>):</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>points = np.array([<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>])
-[ <span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span> ]
-<span class="hljs-meta">&gt;&gt;&gt; </span>wrapped_points = points.reshape(<span class="hljs-number">3</span>, <span class="hljs-number">1</span>)
-[[<span class="hljs-number">0.1</span>], [<span class="hljs-number">0.6</span>], [<span class="hljs-number">0.8</span>]]
-<span class="hljs-meta">&gt;&gt;&gt; </span>distances = points - wrapped_points
-[[ <span class="hljs-number">0.</span> ,  <span class="hljs-number">0.5</span>,  <span class="hljs-number">0.7</span>],
- [<span class="hljs-number">-0.5</span>,  <span class="hljs-number">0.</span> ,  <span class="hljs-number">0.2</span>],
- [<span class="hljs-number">-0.7</span>, <span class="hljs-number">-0.2</span>,  <span class="hljs-number">0.</span> ]]
-<span class="hljs-meta">&gt;&gt;&gt; </span>distances = np.abs(distances)
-[[ <span class="hljs-number">0.</span> ,  <span class="hljs-number">0.5</span>,  <span class="hljs-number">0.7</span>],
- [ <span class="hljs-number">0.5</span>,  <span class="hljs-number">0.</span> ,  <span class="hljs-number">0.2</span>],
- [ <span class="hljs-number">0.7</span>,  <span class="hljs-number">0.2</span>,  <span class="hljs-number">0.</span> ]]
-<span class="hljs-meta">&gt;&gt;&gt; </span>distances[range(<span class="hljs-number">3</span>), range(<span class="hljs-number">3</span>)] = np.inf
-[[ inf,  <span class="hljs-number">0.5</span>,  <span class="hljs-number">0.7</span>],
- [ <span class="hljs-number">0.5</span>,  inf,  <span class="hljs-number">0.2</span>],
- [ <span class="hljs-number">0.7</span>,  <span class="hljs-number">0.2</span>,  inf]]
-<span class="hljs-meta">&gt;&gt;&gt; </span>distances.argmin(<span class="hljs-number">1</span>)
-[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">1</span>]
+<div><h3 id="broadcasting">Broadcasting</h3><p><strong>A set of rules by which NumPy functions operate on arrays of different shapes.</strong></p><pre><code class="python language-python hljs">left  = np.array([<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>])                     <span class="hljs-comment"># `left.shape  == (3,)`</span>
+right = np.array([[<span class="hljs-number">0.1</span>], [<span class="hljs-number">0.6</span>], [<span class="hljs-number">0.8</span>]])                 <span class="hljs-comment"># `right.shape == (3, 1)`</span>
+</code></pre></div>
+
+
+<div><h4 id="1ifarrayshapesdifferinlengthleftpadtheshortershapewithones">1. If array shapes differ in length, left-pad the shorter shape with ones:</h4><pre><code class="python language-python hljs">left  = np.array([[<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>]])                   <span class="hljs-comment"># `left.shape  == (1, 3)`</span>
+right = np.array([[<span class="hljs-number">0.1</span>], [<span class="hljs-number">0.6</span>], [<span class="hljs-number">0.8</span>]])                 <span class="hljs-comment"># `right.shape == (3, 1)`</span>
+</code></pre></div>
+
+<div><h4 id="2ifanydimensionsdifferinsizeexpandtheonesthathavesize1byduplicatingtheirelements">2. If any dimensions differ in size, expand the ones that have size 1 by duplicating their elements:</h4><pre><code class="python language-python hljs">left  = np.array([[<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>],                    <span class="hljs-comment"># `left.shape  == (3, 3)`</span>
+                  [<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>],
+                  [<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>]])
+
+right = np.array([[<span class="hljs-number">0.1</span>,  <span class="hljs-number">0.1</span>,  <span class="hljs-number">0.1</span>],                    <span class="hljs-comment"># `right.shape == (3, 3)`</span>
+                  [<span class="hljs-number">0.6</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.6</span>],
+                  [<span class="hljs-number">0.8</span>,  <span class="hljs-number">0.8</span>,  <span class="hljs-number">0.8</span>]])
+</code></pre></div>
+
+<div><h3 id="example-3">Example</h3><div><h4 id="foreachpointreturnsindexofitsnearestpoint010608121">For each point returns index of its nearest point (<code class="python hljs">[<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>] =&gt; [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">1</span>]</code>):</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>print(points := np.array([<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>]))
+[<span class="hljs-number">0.1</span>  <span class="hljs-number">0.6</span>  <span class="hljs-number">0.8</span>]
+<span class="hljs-meta">&gt;&gt;&gt; </span>print(wrapped_points := points.reshape(<span class="hljs-number">3</span>, <span class="hljs-number">1</span>))
+[[<span class="hljs-number">0.1</span>]
+ [<span class="hljs-number">0.6</span>]
+ [<span class="hljs-number">0.8</span>]]
+<span class="hljs-meta">&gt;&gt;&gt; </span>print(deltas := points - wrapped_points)
+[[ <span class="hljs-number">0.</span>   <span class="hljs-number">0.5</span>  <span class="hljs-number">0.7</span>]
+ [<span class="hljs-number">-0.5</span>  <span class="hljs-number">0.</span>   <span class="hljs-number">0.2</span>]
+ [<span class="hljs-number">-0.7</span> <span class="hljs-number">-0.2</span>  <span class="hljs-number">0.</span> ]]
+<span class="hljs-meta">&gt;&gt;&gt; </span>deltas[range(<span class="hljs-number">3</span>), range(<span class="hljs-number">3</span>)] = np.inf
+<span class="hljs-meta">&gt;&gt;&gt; </span>print(distances := np.abs(deltas))
+[[inf  <span class="hljs-number">0.5</span>  <span class="hljs-number">0.7</span>]
+ [<span class="hljs-number">0.5</span>  inf  <span class="hljs-number">0.2</span>]
+ [<span class="hljs-number">0.7</span>  <span class="hljs-number">0.2</span>  inf]]
+<span class="hljs-meta">&gt;&gt;&gt; </span>print(distances.argmin(axis=<span class="hljs-number">1</span>))
+[<span class="hljs-number">1</span> <span class="hljs-number">2</span> <span class="hljs-number">1</span>]
 </code></pre></div></div>
 
 
@@ -2262,8 +2266,8 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 <pre><code class="python language-python hljs">&lt;Image&gt; = Image.new(<span class="hljs-string">'&lt;mode&gt;'</span>, (width, height))  <span class="hljs-comment"># Creates new image. Also `color=&lt;int/tuple&gt;`.</span>
 &lt;Image&gt; = Image.open(&lt;path&gt;)                    <span class="hljs-comment"># Identifies format based on file's contents.</span>
 &lt;Image&gt; = &lt;Image&gt;.convert(<span class="hljs-string">'&lt;mode&gt;'</span>)             <span class="hljs-comment"># Converts image to the new mode (see Modes).</span>
-&lt;Image&gt;.save(&lt;path&gt;)                            <span class="hljs-comment"># Selects format based on extension (PNG/JPG…).</span>
-&lt;Image&gt;.show()                                  <span class="hljs-comment"># Opens image in the default preview app.</span>
+&lt;Image&gt;.save(&lt;path&gt;)                            <span class="hljs-comment"># Accepts `quality=&lt;int&gt;` if extension is jpg.</span>
+&lt;Image&gt;.show()                                  <span class="hljs-comment"># Displays image in default preview app.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;int/tup&gt; = &lt;Image&gt;.getpixel((x, y))            <span class="hljs-comment"># Returns pixel's value (its color).</span>
 &lt;ImgCore&gt; = &lt;Image&gt;.getdata()                   <span class="hljs-comment"># Returns a flattened view of pixel values.</span>
@@ -2275,12 +2279,12 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 &lt;Image&gt; = &lt;Enhance&gt;.enhance(&lt;float&gt;)            <span class="hljs-comment"># Use ImageEnhance.&lt;name&gt;(&lt;Image&gt;) for Enhance.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;array&gt; = np.array(&lt;Image&gt;)                     <span class="hljs-comment"># Creates a 2d/3d NumPy array from the image.</span>
-&lt;Image&gt; = Image.fromarray(np.uint8(&lt;array&gt;))    <span class="hljs-comment"># Use `&lt;array&gt;.clip(0, 255)` to clip values.</span>
+&lt;Image&gt; = Image.fromarray(np.uint8(&lt;array&gt;))    <span class="hljs-comment"># Use &lt;array&gt;.clip(0, 255) to clip the values.</span>
 </code></pre>
 <div><h3 id="modes-1">Modes</h3><ul>
-<li><strong><code class="python hljs"><span class="hljs-string">'L'</span></code> - Lightness (greyscale image). Each pixel is an int between 0 and 255.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'RGB'</span></code> - Red, green, blue (true color image). Each pixel is a tuple of three ints.</strong></li>
-<li><strong><code class="python hljs"><span class="hljs-string">'RGBA'</span></code> - RGB with alpha. Low alpha (i.e. forth int) makes pixels more transparent.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'L'</span></code> - Lightness (greyscale image). Each pixel is an integer between 0 and 255.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'RGB'</span></code> - Red, green, blue (true color image). Each pixel is a tuple of three integers.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'RGBA'</span></code> - RGB with alpha. Low alpha (i.e. fourth int) makes pixel more transparent.</strong></li>
 <li><strong><code class="python hljs"><span class="hljs-string">'HSV'</span></code> - Hue, saturation, value. Three ints representing color in HSV color space.</strong></li>
 </ul><div><h3 id="examples">Examples</h3><div><h4 id="createsapngimageofarainbowgradient">Creates a PNG image of a rainbow gradient:</h4><pre><code class="python language-python hljs">WIDTH, HEIGHT = <span class="hljs-number">100</span>, <span class="hljs-number">100</span>
 n_pixels = WIDTH * HEIGHT
@@ -2302,13 +2306,13 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 
 <div><h3 id="imagedraw">Image Draw</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> PIL <span class="hljs-keyword">import</span> ImageDraw
 &lt;Draw&gt; = ImageDraw.Draw(&lt;Image&gt;)                <span class="hljs-comment"># Object for adding 2D graphics to the image.</span>
-&lt;Draw&gt;.point((x, y))                            <span class="hljs-comment"># Draws a point. Truncates floats into ints.</span>
-&lt;Draw&gt;.line((x1, y1, x2, y2 [, ...]))           <span class="hljs-comment"># To get anti-aliasing use Image's resize().</span>
+&lt;Draw&gt;.point((x, y))                            <span class="hljs-comment"># Draws a point. Also `fill=&lt;int/tuple/str&gt;`.</span>
+&lt;Draw&gt;.line((x1, y1, x2, y2 [, ...]))           <span class="hljs-comment"># For anti-aliasing use &lt;Image&gt;.resize((w, h)).</span>
 &lt;Draw&gt;.arc((x1, y1, x2, y2), deg1, deg2)        <span class="hljs-comment"># Draws in clockwise dir. Also pieslice().</span>
-&lt;Draw&gt;.rectangle((x1, y1, x2, y2))              <span class="hljs-comment"># To rotate use Image's rotate() and paste().</span>
-&lt;Draw&gt;.polygon((x1, y1, x2, y2, ...))           <span class="hljs-comment"># Last point gets connected to the first.</span>
-&lt;Draw&gt;.ellipse((x1, y1, x2, y2))                <span class="hljs-comment"># Also rounded_rectangle(), regular_polygon().</span>
-&lt;Draw&gt;.text((x, y), &lt;str&gt;, font=&lt;Font&gt;)         <span class="hljs-comment"># `&lt;Font&gt; = ImageFont.truetype(&lt;path&gt;, size)`</span>
+&lt;Draw&gt;.rectangle((x1, y1, x2, y2))              <span class="hljs-comment"># Also rounded_rectangle(), regular_polygon().</span>
+&lt;Draw&gt;.polygon((x1, y1, x2, y2, ...))           <span class="hljs-comment"># Last point gets connected to the first one.</span>
+&lt;Draw&gt;.ellipse((x1, y1, x2, y2))                <span class="hljs-comment"># To rotate use &lt;Image&gt;.rotate(anticlock_deg).</span>
+&lt;Draw&gt;.text((x, y), &lt;str&gt;, font=&lt;Font&gt;)         <span class="hljs-comment"># `&lt;Font&gt; = ImageFont.truetype(&lt;path&gt;, size)`.</span>
 </code></pre></div>
 
 <ul>
@@ -2342,7 +2346,7 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 &lt;int&gt;   = &lt;Wave&gt;.getnchannels()       <span class="hljs-comment"># Returns number of samples per frame.</span>
 &lt;int&gt;   = &lt;Wave&gt;.getsampwidth()       <span class="hljs-comment"># Returns number of bytes per sample.</span>
 &lt;tuple&gt; = &lt;Wave&gt;.getparams()          <span class="hljs-comment"># Returns namedtuple of all parameters.</span>
-&lt;bytes&gt; = &lt;Wave&gt;.readframes(nframes)  <span class="hljs-comment"># Returns next n frames. All if -1.</span>
+&lt;bytes&gt; = &lt;Wave&gt;.readframes(nframes)  <span class="hljs-comment"># Returns all frames if -1 is passed.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;Wave&gt; = wave.open(<span class="hljs-string">'&lt;path&gt;'</span>, <span class="hljs-string">'wb'</span>)    <span class="hljs-comment"># Creates/truncates a file for writing.</span>
 &lt;Wave&gt;.setframerate(&lt;int&gt;)            <span class="hljs-comment"># Pass 44100 for CD, 48000 for video.</span>
@@ -2374,14 +2378,14 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
         p = file.getparams()
         frames = file.readframes(<span class="hljs-number">-1</span>)
     bytes_samples = (frames[i : i + p.sampwidth] <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">0</span>, len(frames), p.sampwidth))
-    <span class="hljs-keyword">return</span> [get_int(b) / pow(<span class="hljs-number">2</span>, p.sampwidth * <span class="hljs-number">8</span> - <span class="hljs-number">1</span>) <span class="hljs-keyword">for</span> b <span class="hljs-keyword">in</span> bytes_samples], p
+    <span class="hljs-keyword">return</span> [get_int(b) / pow(<span class="hljs-number">2</span>, (p.sampwidth * <span class="hljs-number">8</span>) - <span class="hljs-number">1</span>) <span class="hljs-keyword">for</span> b <span class="hljs-keyword">in</span> bytes_samples], p
 </code></pre></div>
 
 <div><h3 id="writefloatsamplestowavfile">Write Float Samples to WAV File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_wav_file</span><span class="hljs-params">(filename, samples_f, p=<span class="hljs-keyword">None</span>, nchannels=<span class="hljs-number">1</span>, sampwidth=<span class="hljs-number">2</span>, framerate=<span class="hljs-number">44100</span>)</span>:</span>
     <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_bytes</span><span class="hljs-params">(a_float)</span>:</span>
         a_float = max(<span class="hljs-number">-1</span>, min(<span class="hljs-number">1</span> - <span class="hljs-number">2e-16</span>, a_float))
-        a_float += p.sampwidth == <span class="hljs-number">1</span>
-        a_float *= pow(<span class="hljs-number">2</span>, p.sampwidth * <span class="hljs-number">8</span> - <span class="hljs-number">1</span>)
+        a_float += (p.sampwidth == <span class="hljs-number">1</span>)
+        a_float *= pow(<span class="hljs-number">2</span>, (p.sampwidth * <span class="hljs-number">8</span>) - <span class="hljs-number">1</span>)
         <span class="hljs-keyword">return</span> int(a_float).to_bytes(p.sampwidth, <span class="hljs-string">'little'</span>, signed=(p.sampwidth != <span class="hljs-number">1</span>))
     <span class="hljs-keyword">if</span> p <span class="hljs-keyword">is</span> <span class="hljs-keyword">None</span>:
         p = wave._wave_params(nchannels, sampwidth, framerate, <span class="hljs-number">0</span>, <span class="hljs-string">'NONE'</span>, <span class="hljs-string">'not compressed'</span>)
@@ -2399,14 +2403,13 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 <div><h4 id="addsnoisetothewavfile">Adds noise to the WAV file:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> uniform
 samples_f, params = read_wav_file(<span class="hljs-string">'test.wav'</span>)
 samples_f = (f + uniform(<span class="hljs-number">-0.05</span>, <span class="hljs-number">0.05</span>) <span class="hljs-keyword">for</span> f <span class="hljs-keyword">in</span> samples_f)
-write_to_wav_file(<span class="hljs-string">'test.wav'</span>, samples_f, params)
+write_to_wav_file(<span class="hljs-string">'test.wav'</span>, samples_f, p=params)
 </code></pre></div>
 
 <div><h4 id="playsthewavfile">Plays the WAV file:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install simpleaudio</span>
 <span class="hljs-keyword">from</span> simpleaudio <span class="hljs-keyword">import</span> play_buffer
 <span class="hljs-keyword">with</span> wave.open(<span class="hljs-string">'test.wav'</span>) <span class="hljs-keyword">as</span> file:
-    p = file.getparams()
-    frames = file.readframes(<span class="hljs-number">-1</span>)
+    frames, p = file.readframes(<span class="hljs-number">-1</span>), file.getparams()
     play_buffer(frames, p.nchannels, p.sampwidth, p.framerate).wait_done()
 </code></pre></div>
 
@@ -2418,52 +2421,55 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 </code></pre></div>
 
 <div><h2 id="synthesizer"><a href="#synthesizer" name="synthesizer">#</a>Synthesizer</h2><div><h4 id="playspopcornbygershonkingsley">Plays Popcorn by Gershon Kingsley:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install simpleaudio</span>
-<span class="hljs-keyword">import</span> array, itertools <span class="hljs-keyword">as</span> it, math, simpleaudio
-
-F  = <span class="hljs-number">44100</span>
-P1 = <span class="hljs-string">'71♩,69♪,,71♩,66♪,,62♩,66♪,,59♩,,,71♩,69♪,,71♩,66♪,,62♩,66♪,,59♩,,,'</span>
-P2 = <span class="hljs-string">'71♩,73♪,,74♩,73♪,,74♪,,71♪,,73♩,71♪,,73♪,,69♪,,71♩,69♪,,71♪,,67♪,,71♩,,,'</span>
-get_pause   = <span class="hljs-keyword">lambda</span> seconds: it.repeat(<span class="hljs-number">0</span>, int(seconds * F))
-sin_f       = <span class="hljs-keyword">lambda</span> i, hz: math.sin(i * <span class="hljs-number">2</span> * math.pi * hz / F)
-get_wave    = <span class="hljs-keyword">lambda</span> hz, seconds: (sin_f(i, hz) <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(int(seconds * F)))
-get_hz      = <span class="hljs-keyword">lambda</span> note: <span class="hljs-number">440</span> * <span class="hljs-number">2</span> ** ((int(note[:<span class="hljs-number">2</span>]) - <span class="hljs-number">69</span>) / <span class="hljs-number">12</span>)
-get_sec     = <span class="hljs-keyword">lambda</span> note: <span class="hljs-number">1</span>/<span class="hljs-number">4</span> <span class="hljs-keyword">if</span> <span class="hljs-string">'♩'</span> <span class="hljs-keyword">in</span> note <span class="hljs-keyword">else</span> <span class="hljs-number">1</span>/<span class="hljs-number">8</span>
-get_samples = <span class="hljs-keyword">lambda</span> note: get_wave(get_hz(note), get_sec(note)) <span class="hljs-keyword">if</span> note <span class="hljs-keyword">else</span> get_pause(<span class="hljs-number">1</span>/<span class="hljs-number">8</span>)
-samples_f   = it.chain.from_iterable(get_samples(n) <span class="hljs-keyword">for</span> n <span class="hljs-keyword">in</span> (P1+P2).split(<span class="hljs-string">','</span>))
-samples_i   = array.array(<span class="hljs-string">'h'</span>, (int(f * <span class="hljs-number">30000</span>) <span class="hljs-keyword">for</span> f <span class="hljs-keyword">in</span> samples_f))
-simpleaudio.play_buffer(samples_i, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, F).wait_done()
+<span class="hljs-keyword">import</span> itertools <span class="hljs-keyword">as</span> it, math, array, simpleaudio
+
+<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">play_notes</span><span class="hljs-params">(notes, bpm=<span class="hljs-number">132</span>, f=<span class="hljs-number">44100</span>)</span>:</span>
+    get_pause   = <span class="hljs-keyword">lambda</span> n_beats: it.repeat(<span class="hljs-number">0</span>, int(n_beats * <span class="hljs-number">60</span>/bpm * f))
+    sin_f       = <span class="hljs-keyword">lambda</span> i, hz: math.sin(i * <span class="hljs-number">2</span> * math.pi * hz / f)
+    get_wave    = <span class="hljs-keyword">lambda</span> hz, n_beats: (sin_f(i, hz) <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(int(n_beats * <span class="hljs-number">60</span>/bpm * f)))
+    get_hz      = <span class="hljs-keyword">lambda</span> note: <span class="hljs-number">440</span> * <span class="hljs-number">2</span> ** ((int(note[:<span class="hljs-number">2</span>]) - <span class="hljs-number">69</span>) / <span class="hljs-number">12</span>)
+    get_nbeats  = <span class="hljs-keyword">lambda</span> note: <span class="hljs-number">1</span>/<span class="hljs-number">2</span> <span class="hljs-keyword">if</span> <span class="hljs-string">'♩'</span> <span class="hljs-keyword">in</span> note <span class="hljs-keyword">else</span> <span class="hljs-number">1</span>/<span class="hljs-number">4</span> <span class="hljs-keyword">if</span> <span class="hljs-string">'♪'</span> <span class="hljs-keyword">in</span> note <span class="hljs-keyword">else</span> <span class="hljs-number">1</span>
+    get_samples = <span class="hljs-keyword">lambda</span> n: get_wave(get_hz(n), get_nbeats(n)) <span class="hljs-keyword">if</span> n <span class="hljs-keyword">else</span> get_pause(<span class="hljs-number">1</span>/<span class="hljs-number">4</span>)
+    samples_f   = it.chain.from_iterable(get_samples(n) <span class="hljs-keyword">for</span> n <span class="hljs-keyword">in</span> notes.split(<span class="hljs-string">','</span>))
+    samples_i   = array.array(<span class="hljs-string">'h'</span>, (int(fl * <span class="hljs-number">5000</span>) <span class="hljs-keyword">for</span> fl <span class="hljs-keyword">in</span> samples_f))
+    simpleaudio.play_buffer(samples_i, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, f).wait_done()
+
+play_notes(<span class="hljs-string">'83♩,81♪,,83♪,,78♪,,74♪,,78♪,,71♪,,,,83♪,,81♪,,83♪,,78♪,,74♪,,78♪,,71♪,,,,'</span>
+           <span class="hljs-string">'83♩,85♪,,86♪,,85♪,,86♪,,83♪,,85♩,83♪,,85♪,,81♪,,83♪,,81♪,,83♪,,79♪,,83♪,,,,'</span>)
 </code></pre></div></div>
 
 
-<div><h2 id="pygame"><a href="#pygame" name="pygame">#</a>Pygame</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pygame</span>
+<div><h2 id="pygame"><a href="#pygame" name="pygame">#</a>Pygame</h2><div><h4 id="opesawindowanddrawsasquarethatcanbemovedwitharrowkeys">Opes a window and draws a square that can be moved with arrow keys:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pygame</span>
 <span class="hljs-keyword">import</span> pygame <span class="hljs-keyword">as</span> pg
 
 pg.init()
 screen = pg.display.set_mode((<span class="hljs-number">500</span>, <span class="hljs-number">500</span>))
 rect = pg.Rect(<span class="hljs-number">240</span>, <span class="hljs-number">240</span>, <span class="hljs-number">20</span>, <span class="hljs-number">20</span>)
 <span class="hljs-keyword">while</span> <span class="hljs-keyword">not</span> pg.event.get(pg.QUIT):
-    deltas = {pg.K_UP: (<span class="hljs-number">0</span>, <span class="hljs-number">-20</span>), pg.K_RIGHT: (<span class="hljs-number">20</span>, <span class="hljs-number">0</span>), pg.K_DOWN: (<span class="hljs-number">0</span>, <span class="hljs-number">20</span>), pg.K_LEFT: (<span class="hljs-number">-20</span>, <span class="hljs-number">0</span>)}
     <span class="hljs-keyword">for</span> event <span class="hljs-keyword">in</span> pg.event.get(pg.KEYDOWN):
-        dx, dy = deltas.get(event.key, (<span class="hljs-number">0</span>, <span class="hljs-number">0</span>))
-        rect = rect.move((dx, dy))
+        dx = (event.key == pg.K_RIGHT) - (event.key == pg.K_LEFT)
+        dy = (event.key == pg.K_DOWN) - (event.key == pg.K_UP)
+        rect = rect.move((dx * <span class="hljs-number">20</span>, dy * <span class="hljs-number">20</span>))
     screen.fill(pg.Color(<span class="hljs-string">'black'</span>))
     pg.draw.rect(screen, pg.Color(<span class="hljs-string">'white'</span>), rect)
     pg.display.flip()
-</code></pre></div>
+pg.quit()
+</code></pre></div></div>
+
 
-<div><h3 id="rectangle">Rectangle</h3><p><strong>Object for storing rectangular coordinates.</strong></p><pre><code class="python language-python hljs">&lt;Rect&gt; = pg.Rect(x, y, width, height)           <span class="hljs-comment"># Floats get truncated into ints.</span>
-&lt;int&gt;  = &lt;Rect&gt;.x/y/centerx/centery/…           <span class="hljs-comment"># Top, right, bottom, left. Allows assignments.</span>
-&lt;tup.&gt; = &lt;Rect&gt;.topleft/center/…                <span class="hljs-comment"># Topright, bottomright, bottomleft. Same.</span>
-&lt;Rect&gt; = &lt;Rect&gt;.move((delta_x, delta_y))        <span class="hljs-comment"># Use move_ip() to move in-place.</span>
+<div><h3 id="rect">Rect</h3><p><strong>Object for storing rectangular coordinates.</strong></p><pre><code class="python language-python hljs">&lt;Rect&gt; = pg.Rect(x, y, width, height)           <span class="hljs-comment"># Creates Rect object. Truncates passed floats.</span>
+&lt;int&gt;  = &lt;Rect&gt;.x/y/centerx/centery/…           <span class="hljs-comment"># `top/right/bottom/left`. Allows assignments.</span>
+&lt;tup.&gt; = &lt;Rect&gt;.topleft/center/…                <span class="hljs-comment"># `topright/bottomright/bottomleft/size`. Same.</span>
+&lt;Rect&gt; = &lt;Rect&gt;.move((delta_x, delta_y))        <span class="hljs-comment"># Use move_ip() to move the rectangle in-place.</span>
 </code></pre></div>
 
 
-<pre><code class="python language-python hljs">&lt;bool&gt; = &lt;Rect&gt;.collidepoint((x, y))            <span class="hljs-comment"># Checks if rectangle contains the point.</span>
-&lt;bool&gt; = &lt;Rect&gt;.colliderect(&lt;Rect&gt;)             <span class="hljs-comment"># Checks if the two rectangles overlap.</span>
+<pre><code class="python language-python hljs">&lt;bool&gt; = &lt;Rect&gt;.collidepoint((x, y))            <span class="hljs-comment"># Checks whether rectangle contains the point.</span>
+&lt;bool&gt; = &lt;Rect&gt;.colliderect(&lt;Rect&gt;)             <span class="hljs-comment"># Checks whether the two rectangles overlap.</span>
 &lt;int&gt;  = &lt;Rect&gt;.collidelist(&lt;list_of_Rect&gt;)     <span class="hljs-comment"># Returns index of first colliding Rect or -1.</span>
 &lt;list&gt; = &lt;Rect&gt;.collidelistall(&lt;list_of_Rect&gt;)  <span class="hljs-comment"># Returns indices of all colliding rectangles.</span>
 </code></pre>
-<div><h3 id="surface">Surface</h3><p><strong>Object for representing images.</strong></p><pre><code class="python language-python hljs">&lt;Surf&gt; = pg.display.set_mode((width, height))   <span class="hljs-comment"># Opens new window and returns its surface.</span>
+<div><h3 id="surface">Surface</h3><p><strong>Object for representing images.</strong></p><pre><code class="python language-python hljs">&lt;Surf&gt; = pg.display.set_mode((width, height))   <span class="hljs-comment"># Opens a new window and returns its surface.</span>
 &lt;Surf&gt; = pg.Surface((width, height))            <span class="hljs-comment"># New RGB surface. RGBA if `flags=pg.SRCALPHA`.</span>
 &lt;Surf&gt; = pg.image.load(&lt;path/file&gt;)             <span class="hljs-comment"># Loads the image. Format depends on source.</span>
 &lt;Surf&gt; = pg.surfarray.make_surface(&lt;np_array&gt;)  <span class="hljs-comment"># Also `&lt;np_arr&gt; = surfarray.pixels3d(&lt;Surf&gt;)`.</span>
@@ -2471,26 +2477,25 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 </code></pre></div>
 
 
-<pre><code class="python language-python hljs">&lt;Surf&gt;.fill(color)                              <span class="hljs-comment"># Tuple, Color('#rrggbb[aa]') or Color(&lt;name&gt;).</span>
+<pre><code class="python language-python hljs">&lt;Surf&gt;.fill(color)                              <span class="hljs-comment"># Pass tuple of ints or pg.Color('&lt;name/hex&gt;').</span>
 &lt;Surf&gt;.set_at((x, y), color)                    <span class="hljs-comment"># Updates pixel. Also &lt;Surf&gt;.get_at((x, y)).</span>
 &lt;Surf&gt;.blit(&lt;Surf&gt;, (x, y))                     <span class="hljs-comment"># Draws passed surface at specified location.</span>
 </code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> pygame.transform <span class="hljs-keyword">import</span> scale, ...
-&lt;Surf&gt; = scale(&lt;Surf&gt;, (width, height))         <span class="hljs-comment"># Returns scaled surface.</span>
-&lt;Surf&gt; = rotate(&lt;Surf&gt;, anticlock_degrees)      <span class="hljs-comment"># Returns rotated and scaled surface.</span>
-&lt;Surf&gt; = flip(&lt;Surf&gt;, x_bool, y_bool)           <span class="hljs-comment"># Returns flipped surface.</span>
+<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> pygame.transform <span class="hljs-keyword">import</span> scale, rotate      <span class="hljs-comment"># Also: flip, smoothscale, scale_by.</span>
+&lt;Surf&gt; = scale(&lt;Surf&gt;, (width, height))         <span class="hljs-comment"># Scales the surface. `smoothscale()` blurs it.</span>
+&lt;Surf&gt; = rotate(&lt;Surf&gt;, angle)                  <span class="hljs-comment"># Rotates the surface for counterclock degrees.</span>
+&lt;Surf&gt; = flip(&lt;Surf&gt;, flip_x=<span class="hljs-keyword">False</span>)             <span class="hljs-comment"># Mirrors the surface. Also `flip_y=False`.</span>
 </code></pre>
-<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> pygame.draw <span class="hljs-keyword">import</span> line, ...
-line(&lt;Surf&gt;, color, (x1, y1), (x2, y2), width)  <span class="hljs-comment"># Draws a line to the surface.</span>
+<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> pygame.draw <span class="hljs-keyword">import</span> line, arc, rect         <span class="hljs-comment"># Also: ellipse, polygon, circle, aaline.</span>
+line(&lt;Surf&gt;, color, (x1, y1), (x2, y2))         <span class="hljs-comment"># Draws a line to the surface. Also `width=1`.</span>
 arc(&lt;Surf&gt;, color, &lt;Rect&gt;, from_rad, to_rad)    <span class="hljs-comment"># Also ellipse(&lt;Surf&gt;, color, &lt;Rect&gt;, width=0).</span>
 rect(&lt;Surf&gt;, color, &lt;Rect&gt;, width=<span class="hljs-number">0</span>)            <span class="hljs-comment"># Also polygon(&lt;Surf&gt;, color, points, width=0).</span>
 </code></pre>
-<div><h3 id="font">Font</h3><pre><code class="python language-python hljs">&lt;Font&gt; = pg.font.Font(&lt;path/file&gt;, size)        <span class="hljs-comment"># Loads TTF file. Pass None for default font.</span>
-&lt;Surf&gt; = &lt;Font&gt;.render(text, antialias, color)  <span class="hljs-comment"># Background color can be specified at the end.</span>
-</code></pre></div>
-
+<pre><code class="python language-python hljs">&lt;Font&gt; = pg.font.Font(&lt;path/file&gt;, size)        <span class="hljs-comment"># Loads TTF file. Pass None for default font.</span>
+&lt;Surf&gt; = &lt;Font&gt;.render(text, antialias, color)  <span class="hljs-comment"># Accepts background color as fourth argument.</span>
+</code></pre>
 <div><h3 id="sound">Sound</h3><pre><code class="python language-python hljs">&lt;Sound&gt; = pg.mixer.Sound(&lt;path/file/bytes&gt;)     <span class="hljs-comment"># WAV file or bytes/array of signed shorts.</span>
-&lt;Sound&gt;.play/stop()                             <span class="hljs-comment"># Also set_volume(&lt;float&gt;), fadeout(msec).</span>
+&lt;Sound&gt;.play/stop()                             <span class="hljs-comment"># Also set_volume(&lt;float&gt;) and fadeout(msec).</span>
 </code></pre></div>
 
 <div><h3 id="basicmariobrothersexample">Basic Mario Brothers Example</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> collections, dataclasses, enum, io, itertools <span class="hljs-keyword">as</span> it, pygame <span class="hljs-keyword">as</span> pg, urllib.request
@@ -2522,19 +2527,19 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">run</span><span class="hljs-params">(screen, images, mario, tiles)</span>:</span>
     clock = pg.time.Clock()
     pressed = set()
-    <span class="hljs-keyword">while</span> <span class="hljs-keyword">not</span> pg.event.get(pg.QUIT) <span class="hljs-keyword">and</span> clock.tick(<span class="hljs-number">28</span>):
-        keys = {pg.K_UP: D.n, pg.K_RIGHT: D.e, pg.K_DOWN: D.s, pg.K_LEFT: D.w}
-        pressed |= {keys.get(e.key) <span class="hljs-keyword">for</span> e <span class="hljs-keyword">in</span> pg.event.get(pg.KEYDOWN)}
-        pressed -= {keys.get(e.key) <span class="hljs-keyword">for</span> e <span class="hljs-keyword">in</span> pg.event.get(pg.KEYUP)}
+    <span class="hljs-keyword">while</span> <span class="hljs-keyword">not</span> pg.event.get(pg.QUIT):
+        clock.tick(<span class="hljs-number">28</span>)
+        pressed |= {e.key <span class="hljs-keyword">for</span> e <span class="hljs-keyword">in</span> pg.event.get(pg.KEYDOWN)}
+        pressed -= {e.key <span class="hljs-keyword">for</span> e <span class="hljs-keyword">in</span> pg.event.get(pg.KEYUP)}
         update_speed(mario, tiles, pressed)
         update_position(mario, tiles)
         draw(screen, images, mario, tiles)
 
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">update_speed</span><span class="hljs-params">(mario, tiles, pressed)</span>:</span>
     x, y = mario.spd
-    x += <span class="hljs-number">2</span> * ((D.e <span class="hljs-keyword">in</span> pressed) - (D.w <span class="hljs-keyword">in</span> pressed))
+    x += <span class="hljs-number">2</span> * ((pg.K_RIGHT <span class="hljs-keyword">in</span> pressed) - (pg.K_LEFT <span class="hljs-keyword">in</span> pressed))
     x += (x &lt; <span class="hljs-number">0</span>) - (x &gt; <span class="hljs-number">0</span>)
-    y += <span class="hljs-number">1</span> <span class="hljs-keyword">if</span> D.s <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> get_boundaries(mario.rect, tiles) <span class="hljs-keyword">else</span> (D.n <span class="hljs-keyword">in</span> pressed) * <span class="hljs-number">-10</span>
+    y += <span class="hljs-number">1</span> <span class="hljs-keyword">if</span> D.s <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> get_boundaries(mario.rect, tiles) <span class="hljs-keyword">else</span> (pg.K_UP <span class="hljs-keyword">in</span> pressed) * <span class="hljs-number">-10</span>
     mario.spd = P(x=max(-MAX_S.x, min(MAX_S.x, x)), y=max(-MAX_S.y, min(MAX_S.y, y)))
 
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">update_position</span><span class="hljs-params">(mario, tiles)</span>:</span>
@@ -2557,7 +2562,7 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
     screen.fill((<span class="hljs-number">85</span>, <span class="hljs-number">168</span>, <span class="hljs-number">255</span>))
     mario.facing_left = mario.spd.x &lt; <span class="hljs-number">0</span> <span class="hljs-keyword">if</span> mario.spd.x <span class="hljs-keyword">else</span> mario.facing_left
     is_airborne = D.s <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> get_boundaries(mario.rect, tiles)
-    image_index = <span class="hljs-number">4</span> <span class="hljs-keyword">if</span> is_airborne <span class="hljs-keyword">else</span> (next(mario.frame_cycle) <span class="hljs-keyword">if</span> mario.spd.x <span class="hljs-keyword">else</span> <span class="hljs-number">6</span>)
+    image_index = <span class="hljs-number">4</span> <span class="hljs-keyword">if</span> is_airborne <span class="hljs-keyword">else</span> next(mario.frame_cycle) <span class="hljs-keyword">if</span> mario.spd.x <span class="hljs-keyword">else</span> <span class="hljs-number">6</span>
     screen.blit(images[image_index + (mario.facing_left * <span class="hljs-number">9</span>)], mario.rect)
     <span class="hljs-keyword">for</span> t <span class="hljs-keyword">in</span> tiles:
         is_border = t.x <span class="hljs-keyword">in</span> [<span class="hljs-number">0</span>, (W-<span class="hljs-number">1</span>)*<span class="hljs-number">16</span>] <span class="hljs-keyword">or</span> t.y <span class="hljs-keyword">in</span> [<span class="hljs-number">0</span>, (H-<span class="hljs-number">1</span>)*<span class="hljs-number">16</span>]
@@ -2568,7 +2573,7 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
     main()
 </code></pre></div>
 
-<div><h2 id="pandas"><a href="#pandas" name="pandas">#</a>Pandas</h2><p><strong>Data analysis library. For examples see <a href="#displays-a-line-chart-of-total-coronavirus-deaths-per-million-grouped-by-continent">Plotly</a>.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pandas matplotlib</span>
+<div><h2 id="pandas"><a href="#pandas" name="pandas">#</a>Pandas</h2><p><strong>Data analysis library. For examples see <a href="#plotly">Plotly</a>.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pandas matplotlib</span>
 <span class="hljs-keyword">import</span> pandas <span class="hljs-keyword">as</span> pd, matplotlib.pyplot <span class="hljs-keyword">as</span> plt
 </code></pre></div>
 
@@ -2580,9 +2585,8 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 </code></pre></div>
 
 
-<pre><code class="python language-python hljs">&lt;S&gt;  = pd.Series(&lt;list&gt;)                       <span class="hljs-comment"># Assigns RangeIndex starting at 0.</span>
-&lt;S&gt;  = pd.Series(&lt;dict&gt;)                       <span class="hljs-comment"># Takes dictionary's keys for index.</span>
-&lt;S&gt;  = pd.Series(&lt;dict/Series&gt;, index=&lt;list&gt;)  <span class="hljs-comment"># Only keeps items with keys specified in index.</span>
+<pre><code class="python language-python hljs">&lt;S&gt;  = pd.Series(&lt;list&gt;)                       <span class="hljs-comment"># Uses list's indices for 'index'.</span>
+&lt;S&gt;  = pd.Series(&lt;dict&gt;)                       <span class="hljs-comment"># Uses dictionary's keys for 'index'.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;el&gt; = &lt;S&gt;.loc[key]                            <span class="hljs-comment"># Or: &lt;S&gt;.iloc[i]</span>
 &lt;S&gt;  = &lt;S&gt;.loc[coll_of_keys]                   <span class="hljs-comment"># Or: &lt;S&gt;.iloc[coll_of_i]</span>
@@ -2590,23 +2594,26 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 </code></pre>
 <pre><code class="python language-python hljs">&lt;el&gt; = &lt;S&gt;[key/i]                              <span class="hljs-comment"># Or: &lt;S&gt;.&lt;key&gt;</span>
 &lt;S&gt;  = &lt;S&gt;[coll_of_keys/coll_of_i]             <span class="hljs-comment"># Or: &lt;S&gt;[key/i : key/i]</span>
-&lt;S&gt;  = &lt;S&gt;[bools]                              <span class="hljs-comment"># Or: &lt;S&gt;.loc/iloc[bools]</span>
+&lt;S&gt;  = &lt;S&gt;[&lt;S_of_bools&gt;]                       <span class="hljs-comment"># Or: &lt;S&gt;.loc/iloc[&lt;S_of_bools&gt;]</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;S&gt;  = &lt;S&gt; &gt; &lt;el/S&gt;                            <span class="hljs-comment"># Returns a Series of bools.</span>
+<pre><code class="python language-python hljs">&lt;S&gt;  = &lt;S&gt; &gt; &lt;el/S&gt;                            <span class="hljs-comment"># Returns S of bools. For logic use &amp;, |, ~.</span>
 &lt;S&gt;  = &lt;S&gt; + &lt;el/S&gt;                            <span class="hljs-comment"># Items with non-matching keys get value NaN.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;S&gt; = pd.concat(&lt;coll_of_S&gt;)                   <span class="hljs-comment"># Concats multiple series into one long Series.</span>
-&lt;S&gt; = &lt;S&gt;.combine_first(&lt;S&gt;)                   <span class="hljs-comment"># Adds items that are not yet present.</span>
-&lt;S&gt;.update(&lt;S&gt;)                                <span class="hljs-comment"># Updates items that are already present.</span>
+<pre><code class="python language-python hljs">&lt;S&gt;  = &lt;S&gt;.head/describe/sort_values()         <span class="hljs-comment"># Also &lt;S&gt;.unique/value_counts/round/dropna().</span>
+&lt;S&gt;  = &lt;S&gt;.str.strip/lower/contains/replace()  <span class="hljs-comment"># Also split().str[i] or split(expand=True).</span>
+&lt;S&gt;  = &lt;S&gt;.dt.year/month/day/hour              <span class="hljs-comment"># Use pd.to_datetime(&lt;S&gt;) to get S of datetimes.</span>
+&lt;S&gt;  = &lt;S&gt;.dt.to_period(<span class="hljs-string">'y/m/d/h'</span>)             <span class="hljs-comment"># Quantizes datetimes into Period objects.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;S&gt;.plot.line/area/bar/pie/hist()              <span class="hljs-comment"># Generates a Matplotlib plot.</span>
+<pre><code class="python language-python hljs">&lt;S&gt;.plot.line/area/bar/pie/hist()              <span class="hljs-comment"># Generates a plot. Accepts `title=&lt;str&gt;`.</span>
 plt.show()                                     <span class="hljs-comment"># Displays the plot. Also plt.savefig(&lt;path&gt;).</span>
 </code></pre>
 <ul>
-<li><strong>Indexing objects can't be tuples because <code class="python hljs"><span class="hljs-string">'obj[x, y]'</span></code> is converted to <code class="python hljs"><span class="hljs-string">'obj[(x, y)]'</span></code>!</strong></li>
-<li><strong>Pandas uses NumPy types like <code class="python hljs"><span class="hljs-string">'np.int64'</span></code>. Series is converted to <code class="python hljs"><span class="hljs-string">'float64'</span></code> if we assign np.nan to any item. Use <code class="python hljs"><span class="hljs-string">'&lt;S&gt;.astype(&lt;str/type&gt;)'</span></code> to get converted Series.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'print(&lt;S&gt;.to_string())'</span></code> to print a Series that has more than sixty items.</strong></li>
+<li><strong>Use <code class="python hljs"><span class="hljs-string">'&lt;S&gt;.index'</span></code> to get collection of keys and <code class="python hljs"><span class="hljs-string">'&lt;S&gt;.index = &lt;coll&gt;'</span></code> to update them.</strong></li>
+<li><strong>Only pass a list or Series to loc/iloc because <code class="python hljs"><span class="hljs-string">'obj[x, y]'</span></code> is converted to <code class="python hljs"><span class="hljs-string">'obj[(x, y)]'</span></code> and <code class="python hljs"><span class="hljs-string">'&lt;S&gt;.loc[key_1, key_2]'</span></code> is how you retrieve a value from a multi-indexed Series.</strong></li>
+<li><strong>Pandas uses NumPy types like <code class="python hljs"><span class="hljs-string">'np.int64'</span></code>. Series is converted to <code class="python hljs"><span class="hljs-string">'float64'</span></code> if np.nan is assigned to any item. Use <code class="python hljs"><span class="hljs-string">'&lt;S&gt;.astype(&lt;str/type&gt;)'</span></code> to get converted Series.</strong></li>
 </ul>
-<div><h4 id="seriesaggregatetransformmap">Series — Aggregate, Transform, Map:</h4><pre><code class="python language-python hljs">&lt;el&gt; = &lt;S&gt;.sum/max/mean/idxmax/all()           <span class="hljs-comment"># Or: &lt;S&gt;.agg(lambda &lt;S&gt;: &lt;el&gt;)</span>
+<div><h4 id="seriesaggregatetransformmap">Series — Aggregate, Transform, Map:</h4><pre><code class="python language-python hljs">&lt;el&gt; = &lt;S&gt;.sum/max/mean/std/idxmax/count()     <span class="hljs-comment"># Or: &lt;S&gt;.agg(lambda &lt;S&gt;: &lt;el&gt;)</span>
 &lt;S&gt;  = &lt;S&gt;.rank/diff/cumsum/ffill/interpol…()  <span class="hljs-comment"># Or: &lt;S&gt;.agg/transform(lambda &lt;S&gt;: &lt;S&gt;)</span>
 &lt;S&gt;  = &lt;S&gt;.isna/fillna/isin([&lt;el/coll&gt;])       <span class="hljs-comment"># Or: &lt;S&gt;.agg/transform/map(lambda &lt;el&gt;: &lt;el&gt;)</span>
 </code></pre></div>
@@ -2627,11 +2634,7 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 ┗━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
 </code></pre>
 
-<ul>
-<li><strong>Methods ffill(), interpolate(), fillna() and dropna() accept <code class="python hljs"><span class="hljs-string">'inplace=True'</span></code>.</strong></li>
-<li><strong>Last result has a multi-index. Use <code class="python hljs"><span class="hljs-string">'&lt;S&gt;[key_1, key_2]'</span></code> to get its values.</strong></li>
-</ul>
-<div><h3 id="dataframe">DataFrame</h3><p><strong>Table with labeled rows and columns.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>l = pd.DataFrame([[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>], [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]], index=[<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>], columns=[<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>]); l
+<div><h3 id="dataframe">DataFrame</h3><p><strong>Table with labeled rows and columns.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>df = pd.DataFrame([[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>], [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]], index=[<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>], columns=[<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>]); df
    x  y
 a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>
 b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>
@@ -2647,10 +2650,10 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 &lt;DF&gt;   = &lt;DF&gt;.loc[row_bools, col_bools]        <span class="hljs-comment"># Or: &lt;DF&gt;.iloc[row_bools, col_bools]</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;S/DF&gt; = &lt;DF&gt;[col_key/s]                       <span class="hljs-comment"># Or: &lt;DF&gt;.&lt;col_key&gt;</span>
-&lt;DF&gt;   = &lt;DF&gt;[row_bools]                       <span class="hljs-comment"># Keeps rows as specified by bools.</span>
+&lt;DF&gt;   = &lt;DF&gt;[&lt;S_of_bools&gt;]                    <span class="hljs-comment"># Filters rows. For example `df[df.x &gt; 1]`.</span>
 &lt;DF&gt;   = &lt;DF&gt;[&lt;DF_of_bools&gt;]                   <span class="hljs-comment"># Assigns NaN to items that are False in bools.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;DF&gt;   = &lt;DF&gt; &gt; &lt;el/S/DF&gt;                      <span class="hljs-comment"># Returns DF of bools. S is treated as a row.</span>
+<pre><code class="python language-python hljs">&lt;DF&gt;   = &lt;DF&gt; &gt; &lt;el/S/DF&gt;                      <span class="hljs-comment"># Returns DF of bools. Treats series as a row.</span>
 &lt;DF&gt;   = &lt;DF&gt; + &lt;el/S/DF&gt;                      <span class="hljs-comment"># Items with non-matching keys get value NaN.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;DF&gt;   = &lt;DF&gt;.set_index(col_key)               <span class="hljs-comment"># Replaces row keys with column's values.</span>
@@ -2658,102 +2661,103 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 &lt;DF&gt;   = &lt;DF&gt;.sort_index(ascending=<span class="hljs-keyword">True</span>)       <span class="hljs-comment"># Sorts rows by row keys. Use `axis=1` for cols.</span>
 &lt;DF&gt;   = &lt;DF&gt;.sort_values(col_key/s)           <span class="hljs-comment"># Sorts rows by passed column/s. Also `axis=1`.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;DF&gt;   = &lt;DF&gt;.head/tail/sample(&lt;int&gt;)          <span class="hljs-comment"># Returns first, last, or random n elements.</span>
-&lt;DF&gt;   = &lt;DF&gt;.describe()                       <span class="hljs-comment"># Describes columns. Also shape, info(), corr().</span>
-&lt;DF&gt;   = &lt;DF&gt;.query(<span class="hljs-string">'&lt;query&gt;'</span>)                 <span class="hljs-comment"># Filters rows with e.g. 'col_1 == val_1 and …'.</span>
+<pre><code class="python language-python hljs">&lt;DF&gt;   = &lt;DF&gt;.head/tail/sample(&lt;int&gt;)          <span class="hljs-comment"># Returns first, last, or random n rows.</span>
+&lt;DF&gt;   = &lt;DF&gt;.describe()                       <span class="hljs-comment"># Describes columns. Also info(), corr(), shape.</span>
+&lt;DF&gt;   = &lt;DF&gt;.query(<span class="hljs-string">'&lt;query&gt;'</span>)                 <span class="hljs-comment"># Filters rows. For example `df.query('x &gt; 1')`.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;DF&gt;.plot.line/area/bar/scatter(x=col_key, …)  <span class="hljs-comment"># `y=col_key/s`. Also hist/box(by=col_key).</span>
+<pre><code class="python language-python hljs">&lt;DF&gt;.plot.line/area/bar/scatter(x=col_key, …)  <span class="hljs-comment"># `y=col_key/s`. Also hist/box(column/by=col_k).</span>
 plt.show()                                     <span class="hljs-comment"># Displays the plot. Also plt.savefig(&lt;path&gt;).</span>
 </code></pre>
-<div><h4 id="dataframemergejoinconcat">DataFrame — Merge, Join, Concat:</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>r = pd.DataFrame([[<span class="hljs-number">4</span>, <span class="hljs-number">5</span>], [<span class="hljs-number">6</span>, <span class="hljs-number">7</span>]], index=[<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>], columns=[<span class="hljs-string">'y'</span>, <span class="hljs-string">'z'</span>]); r
+<div><h4 id="dataframemergejoinconcat">DataFrame — Merge, Join, Concat:</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>df_2 = pd.DataFrame([[<span class="hljs-number">4</span>, <span class="hljs-number">5</span>], [<span class="hljs-number">6</span>, <span class="hljs-number">7</span>]], index=[<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>], columns=[<span class="hljs-string">'y'</span>, <span class="hljs-string">'z'</span>]); df_2
    y  z
 b  <span class="hljs-number">4</span>  <span class="hljs-number">5</span>
 c  <span class="hljs-number">6</span>  <span class="hljs-number">7</span>
 </code></pre></div>
 
-<pre><code class="python hljs">┏━━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━┓
-┃                        │    <span class="hljs-string">'outer'</span>    │   <span class="hljs-string">'inner'</span>  │   <span class="hljs-string">'left'</span>   │       Description        ┃
-┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
-┃ l.merge(r, on=<span class="hljs-string">'y'</span>,     │    x   y   z  │ x   y   z  │ x   y   z  │ Merges on column if <span class="hljs-string">'on'</span> ┃
-┃            how=…)      │ <span class="hljs-number">0</span>  <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │ <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │ <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │ or <span class="hljs-string">'left/right_on'</span> are   ┃
-┃                        │ <span class="hljs-number">1</span>  <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │            │ <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │ set, else on shared cols.┃
-┃                        │ <span class="hljs-number">2</span>  .   <span class="hljs-number">6</span>   <span class="hljs-number">7</span>  │            │            │ Uses <span class="hljs-string">'inner'</span> by default. ┃
-┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
-┃ l.join(r, lsuffix=<span class="hljs-string">'l'</span>, │    x yl yr  z │            │ x yl yr  z │ Merges on row keys.      ┃
-┃           rsuffix=<span class="hljs-string">'r'</span>, │ a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ x yl yr  z │ <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ Uses <span class="hljs-string">'left'</span> by default.  ┃
-┃           how=…)       │ b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ If r is a Series, it is  ┃
-┃                        │ c  .  .  <span class="hljs-number">6</span>  <span class="hljs-number">7</span> │            │            │ treated as a column.     ┃
-┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
-┃ pd.concat([l, r],      │    x   y   z  │     y      │            │ Adds rows at the bottom. ┃
-┃           axis=<span class="hljs-number">0</span>,      │ a  <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │     <span class="hljs-number">2</span>      │            │ Uses <span class="hljs-string">'outer'</span> by default. ┃
-┃           join=…)      │ b  <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   .  │     <span class="hljs-number">4</span>      │            │ A Series is treated as a ┃
-┃                        │ b  .   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │     <span class="hljs-number">4</span>      │            │ column. To add a row use ┃
-┃                        │ c  .   <span class="hljs-number">6</span>   <span class="hljs-number">7</span>  │     <span class="hljs-number">6</span>      │            │ pd.concat([l, DF([s])]). ┃
-┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
-┃ pd.concat([l, r],      │    x  y  y  z │            │            │ Adds columns at the      ┃
-┃           axis=<span class="hljs-number">1</span>,      │ a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ x  y  y  z │            │ right end. Uses <span class="hljs-string">'outer'</span>  ┃
-┃           join=…)      │ b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │            │ by default. A Series is  ┃
-┃                        │ c  .  .  <span class="hljs-number">6</span>  <span class="hljs-number">7</span> │            │            │ treated as a column.     ┃
-┗━━━━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━━━━━━━━┛
-</code></pre>
-<div><h4 id="dataframeaggregatetransformmap">DataFrame — Aggregate, Transform, Map:</h4><pre><code class="python language-python hljs">&lt;S&gt;  = &lt;DF&gt;.sum/max/mean/idxmax/all()          <span class="hljs-comment"># Or: &lt;DF&gt;.apply/agg(lambda &lt;S&gt;: &lt;el&gt;)</span>
+<pre><code class="python hljs">┏━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+┃                       │    <span class="hljs-string">'outer'</span>    │   <span class="hljs-string">'inner'</span>  │   <span class="hljs-string">'left'</span>   │       Description         ┃
+┠───────────────────────┼───────────────┼────────────┼────────────┼───────────────────────────┨
+┃ df.merge(df_2,        │    x   y   z  │ x   y   z  │ x   y   z  │ Merges on column if 'on'  ┃
+┃          on=<span class="hljs-string">'y'</span>,      │ <span class="hljs-number">0</span>  <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │ <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │ <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │ or 'left_on/right_on' are ┃
+┃          how=…)       │ <span class="hljs-number">1</span>  <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │            │ <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │ set, else on shared cols. ┃
+┃                       │ <span class="hljs-number">2</span>  .   <span class="hljs-number">6</span>   <span class="hljs-number">7</span>  │            │            │ Uses <span class="hljs-string">'inner'</span> by default.  ┃
+┠───────────────────────┼───────────────┼────────────┼────────────┼───────────────────────────┨
+┃ df.join(df_2,         │    x yl yr  z │            │ x yl yr  z │ Merges on row keys.       ┃
+┃         lsuffix=<span class="hljs-string">'l'</span>,  │ a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ x yl yr  z │ <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ Uses <span class="hljs-string">'left'</span> by default.   ┃
+┃         rsuffix=<span class="hljs-string">'r'</span>,  │ b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ If Series is passed, it   ┃
+┃         how=…)        │ c  .  .  <span class="hljs-number">6</span>  <span class="hljs-number">7</span> │            │            │ is treated as a column.   ┃
+┠───────────────────────┼───────────────┼────────────┼────────────┼───────────────────────────┨
+┃ pd.concat([df, df_2], │    x   y   z  │     y      │            │ Adds rows at the bottom.  ┃
+┃           axis=<span class="hljs-number">0</span>,     │ a  <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │     <span class="hljs-number">2</span>      │            │ Uses <span class="hljs-string">'outer'</span> by default.  ┃
+┃           join=…)     │ b  <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   .  │     <span class="hljs-number">4</span>      │            │ A Series is treated as a  ┃
+┃                       │ b  .   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │     <span class="hljs-number">4</span>      │            │ column. To add a row use  ┃
+┃                       │ c  .   <span class="hljs-number">6</span>   <span class="hljs-number">7</span>  │     <span class="hljs-number">6</span>      │            │ pd.concat([df, DF([s])]). ┃
+┠───────────────────────┼───────────────┼────────────┼────────────┼───────────────────────────┨
+┃ pd.concat([df, df_2], │    x  y  y  z │            │            │ Adds columns at the       ┃
+┃           axis=<span class="hljs-number">1</span>,     │ a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ x  y  y  z │            │ right end. Uses <span class="hljs-string">'outer'</span>   ┃
+┃           join=…)     │ b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │            │ by default. A Series is   ┃
+┃                       │ c  .  .  <span class="hljs-number">6</span>  <span class="hljs-number">7</span> │            │            │ treated as a column.      ┃
+┗━━━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+</code></pre>
+<div><h4 id="dataframeaggregatetransformmap">DataFrame — Aggregate, Transform, Map:</h4><pre><code class="python language-python hljs">&lt;S&gt;  = &lt;DF&gt;.sum/max/mean/std/idxmax/count()    <span class="hljs-comment"># Or: &lt;DF&gt;.apply/agg(lambda &lt;S&gt;: &lt;el&gt;)</span>
 &lt;DF&gt; = &lt;DF&gt;.rank/diff/cumsum/ffill/interpo…()  <span class="hljs-comment"># Or: &lt;DF&gt;.apply/agg/transform(lambda &lt;S&gt;: &lt;S&gt;)</span>
-&lt;DF&gt; = &lt;DF&gt;.isna/fillna/isin([&lt;el/coll&gt;])      <span class="hljs-comment"># Or: &lt;S&gt;.agg/transform/map(lambda &lt;el&gt;: &lt;el&gt;)</span>
+&lt;DF&gt; = &lt;DF&gt;.isna/fillna/isin([&lt;el/coll&gt;])      <span class="hljs-comment"># Or: &lt;DF&gt;.applymap(lambda &lt;el&gt;: &lt;el&gt;)</span>
 </code></pre></div>
 
-<pre><code class="python hljs">┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
-┃                │     <span class="hljs-string">'sum'</span>     │    [<span class="hljs-string">'sum'</span>]    │ {<span class="hljs-string">'x'</span>: <span class="hljs-string">'sum'</span>}  ┃
-┠────────────────┼───────────────┼───────────────┼───────────────┨
-┃ l.apply(…)     │      x  <span class="hljs-number">4</span>     │        x  y   │     x  <span class="hljs-number">4</span>      ┃
-┃ l.agg(…)       │      y  <span class="hljs-number">6</span>     │   sum  <span class="hljs-number">4</span>  <span class="hljs-number">6</span>   │               ┃
-┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
+<pre><code class="python hljs">┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
+┃                 │     <span class="hljs-string">'sum'</span>     │    [<span class="hljs-string">'sum'</span>]    │ {<span class="hljs-string">'x'</span>: <span class="hljs-string">'sum'</span>}  ┃
+┠─────────────────┼───────────────┼───────────────┼───────────────┨
+┃ df.apply(…)     │      x  <span class="hljs-number">4</span>     │        x  y   │     x  <span class="hljs-number">4</span>      ┃
+┃ df.agg(…)       │      y  <span class="hljs-number">6</span>     │   sum  <span class="hljs-number">4</span>  <span class="hljs-number">6</span>   │               ┃
+┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
 
-┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
-┃                │     <span class="hljs-string">'rank'</span>    │    [<span class="hljs-string">'rank'</span>]   │ {<span class="hljs-string">'x'</span>: <span class="hljs-string">'rank'</span>} ┃
-┠────────────────┼───────────────┼───────────────┼───────────────┨
-┃ l.apply(…)     │               │       x    y  │               ┃
-┃ l.agg(…)       │       x    y  │    rank rank  │         x     ┃
-┃ l.transform(…) │  a  <span class="hljs-number">1.0</span>  <span class="hljs-number">1.0</span>  │  a  <span class="hljs-number">1.0</span>  <span class="hljs-number">1.0</span>  │    a  <span class="hljs-number">1.0</span>     ┃
-┃                │  b  <span class="hljs-number">2.0</span>  <span class="hljs-number">2.0</span>  │  b  <span class="hljs-number">2.0</span>  <span class="hljs-number">2.0</span>  │    b  <span class="hljs-number">2.0</span>     ┃
-┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
+┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
+┃                 │     <span class="hljs-string">'rank'</span>    │    [<span class="hljs-string">'rank'</span>]   │ {<span class="hljs-string">'x'</span>: <span class="hljs-string">'rank'</span>} ┃
+┠─────────────────┼───────────────┼───────────────┼───────────────┨
+┃ df.apply(…)     │               │       x    y  │               ┃
+┃ df.agg(…)       │       x    y  │    rank rank  │         x     ┃
+┃ df.transform(…) │  a  <span class="hljs-number">1.0</span>  <span class="hljs-number">1.0</span>  │  a  <span class="hljs-number">1.0</span>  <span class="hljs-number">1.0</span>  │    a  <span class="hljs-number">1.0</span>     ┃
+┃                 │  b  <span class="hljs-number">2.0</span>  <span class="hljs-number">2.0</span>  │  b  <span class="hljs-number">2.0</span>  <span class="hljs-number">2.0</span>  │    b  <span class="hljs-number">2.0</span>     ┃
+┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
 </code></pre>
 
 <ul>
-<li><strong>All methods operate on columns by default. Pass <code class="python hljs"><span class="hljs-string">'axis=1'</span></code> to process the rows instead.</strong></li>
-<li><strong>Fifth result's columns are indexed with a multi-index. This means we need a tuple of column keys to specify a single column: <code class="python hljs"><span class="hljs-string">'&lt;DF&gt;.loc[row_k, (col_k_1, col_k_2)]'</span></code>.</strong></li>
+<li><strong>Listed methods process the columns unless they receive <code class="python hljs"><span class="hljs-string">'axis=1'</span></code>. Exceptions to this rule are <code class="python hljs"><span class="hljs-string">'&lt;DF&gt;.dropna()'</span></code>, <code class="python hljs"><span class="hljs-string">'&lt;DF&gt;.drop(row_key/s)'</span></code> and <code class="python hljs"><span class="hljs-string">'&lt;DF&gt;.rename(&lt;dict/func&gt;)'</span></code>.</strong></li>
+<li><strong>Fifth result's columns are indexed with a multi-index. This means we need a tuple of column keys to specify a column: <code class="python hljs"><span class="hljs-string">'&lt;DF&gt;.loc[row_key, (col_key_1, col_key_2)]'</span></code>.</strong></li>
 </ul>
-<div><h4 id="dataframemultiindex">DataFrame — Multi-Index:</h4><pre><code class="python language-python hljs">&lt;DF&gt;   = &lt;DF&gt;.xs(row_key, level=&lt;int&gt;)         <span class="hljs-comment"># Rows with key on passed level of multi-index.</span>
-&lt;DF&gt;   = &lt;DF&gt;.xs(row_keys, level=&lt;ints&gt;)       <span class="hljs-comment"># Rows that have first key on first level, etc.</span>
-&lt;DF&gt;   = &lt;DF&gt;.set_index(col_keys)              <span class="hljs-comment"># Combines multiple columns into a multi-index.</span>
-&lt;S/DF&gt; = &lt;DF&gt;.stack/unstack(level=<span class="hljs-number">-1</span>)          <span class="hljs-comment"># Combines col keys with row keys or vice versa.</span>
-&lt;DF&gt;   = &lt;DF&gt;.pivot_table(index=col_key/s, …)  <span class="hljs-comment"># `columns=col_key/s, values=col_key/s`.</span>
+<div><h3 id="multiindex">Multi-Index</h3><pre><code class="python language-python hljs">&lt;DF&gt; = &lt;DF&gt;.loc[row_key_1]                     <span class="hljs-comment"># Or: &lt;DF&gt;.xs(row_key_1)</span>
+&lt;DF&gt; = &lt;DF&gt;.loc[:, (slice(<span class="hljs-keyword">None</span>), col_key_2)]   <span class="hljs-comment"># Or: &lt;DF&gt;.xs(col_key_2, axis=1, level=1)</span>
+&lt;DF&gt; = &lt;DF&gt;.set_index(col_keys)                <span class="hljs-comment"># Creates index from cols. Also `append=False`.</span>
+&lt;DF&gt; = &lt;DF&gt;.pivot_table(index=col_key/s)       <span class="hljs-comment"># `columns=key/s, values=key/s, aggfunc='mean'`.</span>
+&lt;S&gt;  = &lt;DF&gt;.stack/unstack(level=<span class="hljs-number">-1</span>)            <span class="hljs-comment"># Combines col keys with row keys or vice versa.</span>
 </code></pre></div>
 
-<div><h4 id="dataframeencodedecode">DataFrame — Encode, Decode:</h4><pre><code class="python language-python hljs">&lt;DF&gt; = pd.read_json/html(<span class="hljs-string">'&lt;str/path/url&gt;'</span>)     <span class="hljs-comment"># Run `$ pip3 install beautifulsoup4 lxml`.</span>
-&lt;DF&gt; = pd.read_csv(<span class="hljs-string">'&lt;path/url&gt;'</span>)               <span class="hljs-comment"># `header/index_col/dtype/usecols/…=&lt;obj&gt;`.</span>
-&lt;DF&gt; = pd.read_pickle/excel(<span class="hljs-string">'&lt;path/url&gt;'</span>)      <span class="hljs-comment"># Use `sheet_name=None` to get all Excel sheets.</span>
-&lt;DF&gt; = pd.read_sql(<span class="hljs-string">'&lt;table/query&gt;'</span>, &lt;conn.&gt;)   <span class="hljs-comment"># SQLite3/SQLAlchemy connection (see #SQLite).</span>
+<div><h3 id="fileformats">File Formats</h3><pre><code class="python language-python hljs">&lt;S/DF&gt; = pd.read_json/pickle(&lt;path/url/file&gt;)  <span class="hljs-comment"># Also io.StringIO(&lt;str&gt;), io.BytesIO(&lt;bytes&gt;).</span>
+&lt;DF&gt;   = pd.read_csv/excel(&lt;path/url/file&gt;)    <span class="hljs-comment"># Also `header/index_col/dtype/usecols/…=&lt;obj&gt;`.</span>
+&lt;list&gt; = pd.read_html(&lt;path/url/file&gt;)         <span class="hljs-comment"># Raises ImportError if webpage has zero tables.</span>
+&lt;S/DF&gt; = pd.read_parquet/feather/hdf(&lt;path…&gt;)  <span class="hljs-comment"># Function read_hdf() accepts `key=&lt;s/df_name&gt;`.</span>
+&lt;DF&gt;   = pd.read_sql(<span class="hljs-string">'&lt;table/query&gt;'</span>, &lt;conn&gt;)  <span class="hljs-comment"># Pass SQLite3/Alchemy connection. See #SQLite.</span>
 </code></pre></div>
 
-<pre><code class="python language-python hljs">&lt;dict&gt; = &lt;DF&gt;.to_dict(<span class="hljs-string">'d/l/s/…'</span>)               <span class="hljs-comment"># Returns columns as dicts, lists or series.</span>
-&lt;str&gt;  = &lt;DF&gt;.to_json/html/csv/latex()         <span class="hljs-comment"># Saves output to a file if path is passed.</span>
-&lt;DF&gt;.to_pickle/excel(&lt;path&gt;)                   <span class="hljs-comment"># Run `$ pip3 install "pandas[excel]" odfpy`.</span>
+<pre><code class="python language-python hljs">&lt;DF&gt;.to_json/csv/html/latex/parquet(&lt;path&gt;)    <span class="hljs-comment"># Returns a string/bytes if path is omitted.</span>
+&lt;DF&gt;.to_pickle/excel/feather/hdf(&lt;path&gt;)       <span class="hljs-comment"># Method to_hdf() requires `key=&lt;s/df_name&gt;`.</span>
 &lt;DF&gt;.to_sql(<span class="hljs-string">'&lt;table_name&gt;'</span>, &lt;connection&gt;)      <span class="hljs-comment"># Also `if_exists='fail/replace/append'`.</span>
 </code></pre>
 <ul>
-<li><strong>Read_csv() only parses dates of columns that were specified by 'parse_dates' argument. It automatically tries to detect the format, but it can be helped with 'date_format' or 'datefirst' arguments. Both dates and datetimes get stored as pd.Timestamp objects.</strong></li>
-<li><strong>If there's a single invalid date then it returns the whole column as a series of strings, unlike <code class="python hljs"><span class="hljs-string">'&lt;S&gt; = pd.to_datetime(&lt;S&gt;, errors="coerce")'</span></code>, which uses pd.NaT.</strong></li>
-<li><strong>To get specific attributes from a series of Timestamps use <code class="python hljs"><span class="hljs-string">'&lt;S&gt;.dt.year/date/…'</span></code>.</strong></li>
+<li><strong><code class="python hljs"><span class="hljs-string">'$ pip3 install "pandas[excel]" odfpy lxml pyarrow'</span></code> installs dependencies.</strong></li>
+<li><strong>Csv functions use the same dialect as standard library's csv module (e.g. <code class="python hljs"><span class="hljs-string">'sep=","'</span></code>).</strong></li>
+<li><strong>Read_csv() only parses dates of columns that are listed in 'parse_dates'. It automatically tries to detect the format, but it can be helped with 'date_format' or 'dayfirst' arguments.</strong></li>
+<li><strong>We get a dataframe with DatetimeIndex if 'parse_dates' argument includes 'index_col'. Its <code class="python hljs"><span class="hljs-string">'resample("y/m/d/h")'</span></code> method returns Resampler object that is similar to GroupBy.</strong></li>
 </ul>
 <div><h3 id="groupby">GroupBy</h3><p><strong>Object that groups together rows of a dataframe based on the value of the passed column.</strong></p><pre><code class="python language-python hljs">&lt;GB&gt; = &lt;DF&gt;.groupby(col_key/s)                 <span class="hljs-comment"># Splits DF into groups based on passed column.</span>
-&lt;DF&gt; = &lt;GB&gt;.apply(&lt;func&gt;)                      <span class="hljs-comment"># Maps each group. Func can return DF, S or el.</span>
+&lt;DF&gt; = &lt;GB&gt;.apply/filter(&lt;func&gt;)               <span class="hljs-comment"># Filter drops a group if func returns False.</span>
 &lt;DF&gt; = &lt;GB&gt;.get_group(&lt;el&gt;)                    <span class="hljs-comment"># Selects a group by grouping column's value.</span>
 &lt;S&gt;  = &lt;GB&gt;.size()                             <span class="hljs-comment"># S of group sizes. Same keys as get_group().</span>
 &lt;GB&gt; = &lt;GB&gt;[col_key]                           <span class="hljs-comment"># Single column GB. All operations return S.</span>
 </code></pre></div>
 
 
-<pre><code class="python language-python hljs">&lt;DF&gt; = &lt;GB&gt;.sum/max/mean/idxmax/all()          <span class="hljs-comment"># Or: &lt;GB&gt;.agg(lambda &lt;S&gt;: &lt;el&gt;)</span>
+<pre><code class="python language-python hljs">&lt;DF&gt; = &lt;GB&gt;.sum/max/mean/std/idxmax/count()    <span class="hljs-comment"># Or: &lt;GB&gt;.agg(lambda &lt;S&gt;: &lt;el&gt;)</span>
 &lt;DF&gt; = &lt;GB&gt;.rank/diff/cumsum/ffill()           <span class="hljs-comment"># Or: &lt;GB&gt;.transform(lambda &lt;S&gt;: &lt;S&gt;)</span>
 &lt;DF&gt; = &lt;GB&gt;.fillna(&lt;el&gt;)                       <span class="hljs-comment"># Or: &lt;GB&gt;.transform(lambda &lt;S&gt;: &lt;S&gt;)</span>
 </code></pre>
@@ -2771,7 +2775,7 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 <span class="hljs-number">6</span>  <span class="hljs-number">11</span>  <span class="hljs-number">13</span></code></pre></div>
 
 <div><h3 id="rolling">Rolling</h3><p><strong>Object for rolling window calculations.</strong></p><pre><code class="python language-python hljs">&lt;RS/RDF/RGB&gt; = &lt;S/DF/GB&gt;.rolling(win_size)     <span class="hljs-comment"># Also: `min_periods=None, center=False`.</span>
-&lt;RS/RDF/RGB&gt; = &lt;RDF/RGB&gt;[col_key/s]            <span class="hljs-comment"># Or: &lt;RDF/RGB&gt;.col_key</span>
+&lt;RS/RDF/RGB&gt; = &lt;RDF/RGB&gt;[col_key/s]            <span class="hljs-comment"># Or: &lt;RDF/RGB&gt;.&lt;col_key&gt;</span>
 &lt;S/DF&gt;       = &lt;R&gt;.mean/sum/max()              <span class="hljs-comment"># Or: &lt;R&gt;.apply/agg(&lt;agg_func/str&gt;)</span>
 </code></pre></div>
 
@@ -2780,18 +2784,18 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 <span class="hljs-keyword">import</span> plotly.express <span class="hljs-keyword">as</span> px, pandas <span class="hljs-keyword">as</span> pd
 </code></pre></div>
 
-<pre><code class="python language-python hljs">&lt;Fig&gt; = px.line(&lt;DF&gt;, x=col_key, y=col_key)            <span class="hljs-comment"># Or: px.line(x=&lt;list&gt;, y=&lt;list&gt;)</span>
-&lt;Fig&gt;.update_layout(margin=dict(t=<span class="hljs-number">0</span>, r=<span class="hljs-number">0</span>, b=<span class="hljs-number">0</span>, l=<span class="hljs-number">0</span>))   <span class="hljs-comment"># Also `paper_bgcolor='rgb(0, 0, 0)'`.</span>
-&lt;Fig&gt;.write_html/json/image(<span class="hljs-string">'&lt;path&gt;'</span>)                  <span class="hljs-comment"># Also &lt;Fig&gt;.show().</span>
+<pre><code class="python language-python hljs">&lt;Fig&gt; = px.line(&lt;DF&gt; [, y=col_key/s [, x=col_key]])   <span class="hljs-comment"># Also px.line(y=&lt;list&gt; [, x=&lt;list&gt;]).</span>
+&lt;Fig&gt;.update_layout(paper_bgcolor=<span class="hljs-string">'#rrggbb'</span>)          <span class="hljs-comment"># Also `margin=dict(t=0, r=0, b=0, l=0)`.</span>
+&lt;Fig&gt;.write_html/json/image(<span class="hljs-string">'&lt;path&gt;'</span>)                 <span class="hljs-comment"># Use &lt;Fig&gt;.show() to display the plot.</span>
 </code></pre>
-<pre><code class="python language-python hljs">&lt;Fig&gt; = px.area/bar/box(&lt;DF&gt;, x=col_key, y=col_key)    <span class="hljs-comment"># Also `color=col_key`.</span>
-&lt;Fig&gt; = px.scatter(&lt;DF&gt;, x=col_key, y=col_key)         <span class="hljs-comment"># Also `color/size/symbol=col_key`.</span>
-&lt;Fig&gt; = px.scatter_3d(&lt;DF&gt;, x=col_key, y=col_key, …)   <span class="hljs-comment"># `z=col_key`. Also color/size/symbol.</span>
-&lt;Fig&gt; = px.histogram(&lt;DF&gt;, x=col_key [, nbins=&lt;int&gt;])  <span class="hljs-comment"># Number of bins depends on DF size.</span>
+<pre><code class="python language-python hljs">&lt;Fig&gt; = px.area/bar/box(&lt;DF&gt;, x=col_key, y=col_keys)  <span class="hljs-comment"># Also `color=col_key`. All are optional.</span>
+&lt;Fig&gt; = px.scatter(&lt;DF&gt;, x=col_key, y=col_keys)       <span class="hljs-comment"># Also `color/size/symbol=col_key`. Same.</span>
+&lt;Fig&gt; = px.scatter_3d(&lt;DF&gt;, x=col_key, y=col_key, …)  <span class="hljs-comment"># `z=col_key`. Also color, size, symbol.</span>
+&lt;Fig&gt; = px.histogram(&lt;DF&gt;, x=col_keys, y=col_key)     <span class="hljs-comment"># Also color, nbins. All are optional.</span>
 </code></pre>
-<div><h4 id="displaysalinechartoftotalcoronavirusdeathspermilliongroupedbycontinent">Displays a line chart of total coronavirus deaths per million grouped by continent:</h4><p></p><div id="2a950764-39fc-416d-97fe-0a6226a3095f" class="plotly-graph-div" style="height:312px; width:914px;"></div><pre><code class="python language-python hljs">covid = pd.read_csv(<span class="hljs-string">'https://raw.githubusercontent.com/owid/covid-19-data/8dde8ca49b'</span>
+<div><h4 id="displaysalinechartoftotalcovid19deathspermilliongroupedbycontinent">Displays a line chart of total COVID-19 deaths per million grouped by continent:</h4><p></p><div id="2a950764-39fc-416d-97fe-0a6226a3095f" class="plotly-graph-div" style="height:312px; width:914px;"></div><pre><code class="python language-python hljs">covid = pd.read_csv(<span class="hljs-string">'https://raw.githubusercontent.com/owid/covid-19-data/8dde8ca49b'</span>
                     <span class="hljs-string">'6e648c17dd420b2726ca0779402651/public/data/owid-covid-data.csv'</span>,
-                    usecols=[<span class="hljs-string">'iso_code'</span>, <span class="hljs-string">'date'</span>, <span class="hljs-string">'total_deaths'</span>, <span class="hljs-string">'population'</span>])
+                    usecols=[<span class="hljs-string">'iso_code'</span>, <span class="hljs-string">'date'</span>, <span class="hljs-string">'population'</span>, <span class="hljs-string">'total_deaths'</span>])
 continents = pd.read_csv(<span class="hljs-string">'https://gto76.github.io/python-cheatsheet/web/continents.csv'</span>,
                          usecols=[<span class="hljs-string">'Three_Letter_Country_Code'</span>, <span class="hljs-string">'Continent_Name'</span>])
 df = pd.merge(covid, continents, left_on=<span class="hljs-string">'iso_code'</span>, right_on=<span class="hljs-string">'Three_Letter_Country_Code'</span>)
@@ -2799,37 +2803,46 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 df[<span class="hljs-string">'Total Deaths per Million'</span>] = df.total_deaths * <span class="hljs-number">1e6</span> / df.population
 df = df[df.date &gt; <span class="hljs-string">'2020-03-14'</span>]
 df = df.rename({<span class="hljs-string">'date'</span>: <span class="hljs-string">'Date'</span>, <span class="hljs-string">'Continent_Name'</span>: <span class="hljs-string">'Continent'</span>}, axis=<span class="hljs-string">'columns'</span>)
-px.line(df, x=<span class="hljs-string">'Date'</span>, y=<span class="hljs-string">'Total Deaths per Million'</span>, color=<span class="hljs-string">'Continent'</span>).show()
+px.line(df, x=<span class="hljs-string">'Date'</span>, y=<span class="hljs-string">'Total Deaths per Million'</span>, color=<span class="hljs-string">'Continent'</span>)
 </code></pre></div>
 
 
 
-<div><h4 id="displaysamultiaxislinechartoftotalcoronaviruscasesandchangesinpricesofbitcoindowjonesandgold">Displays a multi-axis line chart of total coronavirus cases and changes in prices of Bitcoin, Dow Jones and gold:</h4><p></p><div id="e23ccacc-a456-478b-b467-7282a2165921" class="plotly-graph-div" style="height:287px; width:935px;"></div><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> pandas <span class="hljs-keyword">as</span> pd, plotly.graph_objects <span class="hljs-keyword">as</span> go
+<div><h4 id="displaysamultiaxislinechartoftotalcovid19casesandchangesinpricesofbitcoindowjonesandgold">Displays a multi-axis line chart of total COVID-19 cases and changes in prices of Bitcoin, Dow Jones and gold:</h4><p></p><div id="e23ccacc-a456-478b-b467-7282a2165921" class="plotly-graph-div" style="height:285px; width:935px;"></div><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pandas lxml selenium plotly</span>
+<span class="hljs-keyword">import</span> pandas <span class="hljs-keyword">as</span> pd, selenium.webdriver, io, plotly.graph_objects <span class="hljs-keyword">as</span> go
 
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
-    covid, bitcoin, gold, dow = scrape_data()
+    covid, (bitcoin, gold, dow) = get_covid_cases(), get_tickers()
     df = wrangle_data(covid, bitcoin, gold, dow)
     display_data(df)
 
-<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">scrape_data</span><span class="hljs-params">()</span>:</span>
-    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_covid_cases</span><span class="hljs-params">()</span>:</span>
-        url = <span class="hljs-string">'https://covid.ourworldindata.org/data/owid-covid-data.csv'</span>
-        df = pd.read_csv(url, usecols=[<span class="hljs-string">'location'</span>, <span class="hljs-string">'date'</span>, <span class="hljs-string">'total_cases'</span>])
-        df = df[df.location == <span class="hljs-string">'World'</span>]
-        <span class="hljs-keyword">return</span> df.set_index(<span class="hljs-string">'date'</span>).total_cases
-    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_ticker</span><span class="hljs-params">(symbol)</span>:</span>
-        url = (<span class="hljs-string">f'https://query1.finance.yahoo.com/v7/finance/download/<span class="hljs-subst">{symbol}</span>?'</span>
-               <span class="hljs-string">'period1=1579651200&amp;period2=9999999999&amp;interval=1d&amp;events=history'</span>)
-        df = pd.read_csv(url, usecols=[<span class="hljs-string">'Date'</span>, <span class="hljs-string">'Close'</span>])
-        <span class="hljs-keyword">return</span> df.set_index(<span class="hljs-string">'Date'</span>).Close
-    out = get_covid_cases(), get_ticker(<span class="hljs-string">'BTC-USD'</span>), get_ticker(<span class="hljs-string">'GC=F'</span>), get_ticker(<span class="hljs-string">'^DJI'</span>)
-    names = [<span class="hljs-string">'Total Cases'</span>, <span class="hljs-string">'Bitcoin'</span>, <span class="hljs-string">'Gold'</span>, <span class="hljs-string">'Dow Jones'</span>]
-    <span class="hljs-keyword">return</span> map(pd.Series.rename, out, names)
+<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_covid_cases</span><span class="hljs-params">()</span>:</span>
+    url = <span class="hljs-string">'https://catalog.ourworldindata.org/garden/covid/latest/compact/compact.csv'</span>
+    df = pd.read_csv(url, parse_dates=[<span class="hljs-string">'date'</span>])
+    df = df[df.country == <span class="hljs-string">'World'</span>]
+    s = df.set_index(<span class="hljs-string">'date'</span>).total_cases
+    <span class="hljs-keyword">return</span> s.rename(<span class="hljs-string">'Total Cases'</span>)
+
+<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_tickers</span><span class="hljs-params">()</span>:</span>
+    <span class="hljs-keyword">with</span> selenium.webdriver.Chrome() <span class="hljs-keyword">as</span> driver:
+        driver.implicitly_wait(<span class="hljs-number">10</span>)
+        symbols = {<span class="hljs-string">'Bitcoin'</span>: <span class="hljs-string">'BTC-USD'</span>, <span class="hljs-string">'Gold'</span>: <span class="hljs-string">'GC=F'</span>, <span class="hljs-string">'Dow Jones'</span>: <span class="hljs-string">'%5EDJI'</span>}
+        <span class="hljs-keyword">return</span> [get_ticker(driver, name, symbol) <span class="hljs-keyword">for</span> name, symbol <span class="hljs-keyword">in</span> symbols.items()]
+
+<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_ticker</span><span class="hljs-params">(driver, name, symbol)</span>:</span>
+    url = <span class="hljs-string">f'https://finance.yahoo.com/quote/<span class="hljs-subst">{symbol}</span>/history/'</span>
+    driver.get(url + <span class="hljs-string">'?period1=1579651200&amp;period2=9999999999'</span>)
+    <span class="hljs-keyword">if</span> buttons := driver.find_elements(<span class="hljs-string">'xpath'</span>, <span class="hljs-string">'//button[@name="reject"]'</span>):
+        buttons[<span class="hljs-number">0</span>].click()
+    html = io.StringIO(driver.page_source)
+    dataframes = pd.read_html(html, parse_dates=[<span class="hljs-string">'Date'</span>])
+    s = dataframes[<span class="hljs-number">0</span>].set_index(<span class="hljs-string">'Date'</span>).Open
+    <span class="hljs-keyword">return</span> s.rename(name)
 
 <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">wrangle_data</span><span class="hljs-params">(covid, bitcoin, gold, dow)</span>:</span>
     df = pd.concat([bitcoin, gold, dow], axis=<span class="hljs-number">1</span>)  <span class="hljs-comment"># Creates table by joining columns on dates.</span>
-    df = df.sort_index().interpolate()            <span class="hljs-comment"># Sorts table by date and interpolates NaN-s.</span>
-    df = df.loc[<span class="hljs-string">'2020-02-23'</span>:]                    <span class="hljs-comment"># Discards rows before '2020-02-23'.</span>
+    df = df.sort_index().interpolate()            <span class="hljs-comment"># Sorts rows by date and interpolates NaN-s.</span>
+    df = df.loc[<span class="hljs-string">'2020-02-23'</span>:<span class="hljs-string">'2021-12-20'</span>]        <span class="hljs-comment"># Keeps rows between specified dates.</span>
     df = (df / df.iloc[<span class="hljs-number">0</span>]) * <span class="hljs-number">100</span>                  <span class="hljs-comment"># Calculates percentages relative to day 1.</span>
     df = df.join(covid)                           <span class="hljs-comment"># Adds column with covid cases.</span>
     <span class="hljs-keyword">return</span> df.sort_values(df.index[<span class="hljs-number">-1</span>], axis=<span class="hljs-number">1</span>)   <span class="hljs-comment"># Sorts columns by last day's value.</span>
@@ -2838,14 +2851,15 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
     figure = go.Figure()
     <span class="hljs-keyword">for</span> col_name <span class="hljs-keyword">in</span> reversed(df.columns):
         yaxis = <span class="hljs-string">'y1'</span> <span class="hljs-keyword">if</span> col_name == <span class="hljs-string">'Total Cases'</span> <span class="hljs-keyword">else</span> <span class="hljs-string">'y2'</span>
-        trace = go.Scatter(x=df.index, y=df[col_name], name=col_name, yaxis=yaxis)
+        trace = go.Scatter(x=df.index, y=df[col_name], yaxis=yaxis, name=col_name)
         figure.add_trace(trace)
     figure.update_layout(
+        width=<span class="hljs-number">944</span>,
+        height=<span class="hljs-number">423</span>,
         yaxis1=dict(title=<span class="hljs-string">'Total Cases'</span>, rangemode=<span class="hljs-string">'tozero'</span>),
         yaxis2=dict(title=<span class="hljs-string">'%'</span>, rangemode=<span class="hljs-string">'tozero'</span>, overlaying=<span class="hljs-string">'y'</span>, side=<span class="hljs-string">'right'</span>),
-        legend=dict(x=<span class="hljs-number">1.08</span>),
-        width=<span class="hljs-number">944</span>,
-        height=<span class="hljs-number">423</span>
+        colorway=[<span class="hljs-string">'#EF553B'</span>, <span class="hljs-string">'#636EFA'</span>, <span class="hljs-string">'#00CC96'</span>, <span class="hljs-string">'#FFA152'</span>],
+        legend=dict(x=<span class="hljs-number">1.08</span>)
     )
     figure.show()
 
@@ -2855,30 +2869,28 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 
 
 
-<div><h2 id="appendix"><a href="#appendix" name="appendix">#</a>Appendix</h2><div><h3 id="cython">Cython</h3><p><strong>Library that compiles Python code into C.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install cython</span>
-<span class="hljs-keyword">import</span> pyximport; pyximport.install()
-<span class="hljs-keyword">import</span> &lt;cython_script&gt;
-&lt;cython_script&gt;.main()
+<div><h2 id="appendix"><a href="#appendix" name="appendix">#</a>Appendix</h2><div><h3 id="cython">Cython</h3><p><strong>Library that compiles Python-like code into C.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install cython</span>
+<span class="hljs-keyword">import</span> pyximport; pyximport.install()                <span class="hljs-comment"># Module that runs Cython scripts.</span>
+<span class="hljs-keyword">import</span> &lt;cython_script&gt;                               <span class="hljs-comment"># Script must have '.pyx' extension.</span>
 </code></pre></div></div>
 
 
 
-<div><h4 id="definitions">Definitions:</h4><ul>
-<li><strong>All <code class="python hljs"><span class="hljs-string">'cdef'</span></code> definitions are optional, but they contribute to the speed-up.</strong></li>
-<li><strong>Script needs to be saved with a <code class="python hljs"><span class="hljs-string">'pyx'</span></code> extension.</strong></li>
-</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">cdef</span> &lt;ctype&gt; &lt;var_name&gt; = &lt;obj&gt;
-<span class="hljs-keyword">cdef</span> &lt;ctype&gt;[n_elements] &lt;var_name&gt; = [&lt;el_1&gt;, &lt;el_2&gt;, ...]
-<span class="hljs-keyword">cdef</span> &lt;ctype/void&gt; &lt;func_name&gt;(&lt;ctype&gt; &lt;arg_name&gt;): ...
+<div><h4 id="allcdefdefinitionsareoptionalbuttheycontributetothespeedup">All <code class="python hljs"><span class="hljs-string">'cdef'</span></code> definitions are optional, but they contribute to the speed-up:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">cdef</span> &lt;type&gt; &lt;var_name&gt; [= &lt;obj/var&gt;]                 <span class="hljs-comment"># Either Python or C type variable.</span>
+<span class="hljs-keyword">cdef</span> &lt;ctype&gt; *&lt;pointer_name&gt; [= &amp;&lt;var&gt;]              <span class="hljs-comment"># Use &lt;pointer&gt;[0] to get the value.</span>
+<span class="hljs-keyword">cdef</span> &lt;ctype&gt;[size] &lt;array_name&gt; [= &lt;coll/array&gt;]     <span class="hljs-comment"># Also `&lt;ctype&gt;[:] &lt;mview&gt; = &lt;array&gt;`.</span>
+<span class="hljs-keyword">cdef</span> &lt;ctype&gt; *&lt;array_name&gt; [= &lt;coll/array/pointer&gt;]  <span class="hljs-comment"># E.g. `&lt;&lt;ctype&gt; *&gt; malloc(n_bytes)`.</span>
 </code></pre></div>
 
-
-<pre><code class="python language-python hljs"><span class="hljs-keyword">cdef</span> <span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">class_name</span>&gt;:</span>
-    <span class="hljs-keyword">cdef</span> <span class="hljs-keyword">public</span> &lt;ctype&gt; &lt;attr_name&gt;
-    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, &lt;ctype&gt; &lt;arg_name&gt;)</span>:</span>
-        self.&lt;attr_name&gt; = &lt;arg_name&gt;
+<pre><code class="python language-python hljs"><span class="hljs-keyword">cdef</span> &lt;type&gt; &lt;func_name&gt;(&lt;type&gt; [*]&lt;arg_name&gt;): ...   <span class="hljs-comment"># Omitted types default to `object`.</span>
+</code></pre>
+<pre><code class="python language-python hljs"><span class="hljs-keyword">cdef</span> <span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">class_name</span>&gt;:</span>                             <span class="hljs-comment"># Also `cdef struct &lt;struct_name&gt;:`.</span>
+    <span class="hljs-keyword">cdef</span> <span class="hljs-keyword">public</span> &lt;type&gt; [*]&lt;attr_name&gt;                <span class="hljs-comment"># Also `... &lt;ctype&gt; [*]&lt;field_name&gt;`.</span>
+    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, &lt;type&gt; &lt;arg_name&gt;)</span>:</span>           <span class="hljs-comment"># Also `cdef __dealloc__(self):`.</span>
+        self.&lt;attr_name&gt; = &lt;arg_name&gt;                <span class="hljs-comment"># Also `... free(&lt;array/pointer&gt;)`.</span>
 </code></pre>
-<div><h3 id="virtualenvironments">Virtual Environments</h3><p><strong>System for installing libraries directly into project's directory.</strong></p><pre><code class="bash language-bash hljs">$ python3 -m venv NAME      <span class="hljs-comment"># Creates virtual environment in current directory.</span>
-$ <span class="hljs-built_in">source</span> NAME/bin/activate  <span class="hljs-comment"># Activates env. On Windows run `NAME\Scripts\activate`.</span>
+<div><h3 id="virtualenvironments">Virtual Environments</h3><p><strong>System for installing libraries directly into project's directory.</strong></p><pre><code class="python hljs">$ python3 -m venv NAME      <span class="hljs-comment"># Creates virtual environment in current directory.</span>
+$ source NAME/bin/activate  <span class="hljs-comment"># Activates it. On Windows run `NAME\Scripts\activate`.</span>
 $ pip3 install LIBRARY      <span class="hljs-comment"># Installs the library into active environment.</span>
 $ python3 FILE              <span class="hljs-comment"># Runs the script in active environment. Also `./FILE`.</span>
 $ deactivate                <span class="hljs-comment"># Deactivates the active virtual environment.</span>
@@ -2915,15 +2927,14 @@ <h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesandmanualalignment
 </code></pre></div>
 
 
-<div><h2 id="index"><a href="#index" name="index">#</a>Index</h2><ul><li><strong>Only available in the <a href="https://transactions.sendowl.com/products/78175486/4422834F/view">PDF</a>.</strong></li>
-<li><strong>Ctrl+F / ⌘F is usually sufficient.</strong></li>
+<div><h2 id="index"><a href="#index" name="index">#</a>Index</h2><ul><li><strong>Ctrl+F / ⌘F is usually sufficient.</strong></li>
 <li><strong>Searching <code class="python hljs"><span class="hljs-string">'#&lt;title&gt;'</span></code> will limit the search to the titles.</strong></li>
-<li><strong>Click on the <code class="python hljs"><span class="hljs-string">'#'</span></code> symbol to get a link to specific section.</strong></li>
+<li><strong>Click on the title's <code class="python hljs"><span class="hljs-string">'#'</span></code> to get a link to its section.</strong></li>
 </ul></div>
  
 
   <footer>
-    <aside>November 7, 2024</aside>
+    <aside>July 31, 2025</aside>
     <a href="https://gto76.github.io" rel="author">Jure Šorn</a>
   </footer>
 
diff --git a/parse.js b/parse.js
index 50c4790cb..7a7d19c92 100755
--- a/parse.js
+++ b/parse.js
@@ -33,20 +33,19 @@ const TOC =
   '<pre style="border-left: none;padding-left: 1.9px;"><code class="hljs bash" style="line-height: 1.327em;"><strong>ToC</strong> = {\n' +
   '    <strong><span class="hljs-string">\'1. Collections\'</span></strong>: [<a href="#list">List</a>, <a href="#dictionary">Dictionary</a>, <a href="#set">Set</a>, <a href="#tuple">Tuple</a>, <a href="#range">Range</a>, <a href="#enumerate">Enumerate</a>, <a href="#iterator">Iterator</a>, <a href="#generator">Generator</a>],\n' +
   '    <strong><span class="hljs-string">\'2. Types\'</span></strong>:       [<a href="#type">Type</a>, <a href="#string">String</a>, <a href="#regex">Regular_Exp</a>, <a href="#format">Format</a>, <a href="#numbers">Numbers</a>, <a href="#combinatorics">Combinatorics</a>, <a href="#datetime">Datetime</a>],\n' +
-  '    <strong><span class="hljs-string">\'3. Syntax\'</span></strong>:      [<a href="#arguments">Args</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#ducktypes">Duck_Types</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Exception</a>],\n' +
+  '    <strong><span class="hljs-string">\'3. Syntax\'</span></strong>:      [<a href="#function">Function</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#ducktypes">Duck_Type</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Except</a>],\n' +
   '    <strong><span class="hljs-string">\'4. System\'</span></strong>:      [<a href="#exit">Exit</a>, <a href="#print">Print</a>, <a href="#input">Input</a>, <a href="#commandlinearguments">Command_Line_Arguments</a>, <a href="#open">Open</a>, <a href="#paths">Path</a>, <a href="#oscommands">OS_Commands</a>],\n' +
   '    <strong><span class="hljs-string">\'5. Data\'</span></strong>:        [<a href="#json">JSON</a>, <a href="#pickle">Pickle</a>, <a href="#csv">CSV</a>, <a href="#sqlite">SQLite</a>, <a href="#bytes">Bytes</a>, <a href="#struct">Struct</a>, <a href="#array">Array</a>, <a href="#memoryview">Memory_View</a>, <a href="#deque">Deque</a>],\n' +
-  '    <strong><span class="hljs-string">\'6. Advanced\'</span></strong>:    [<a href="#threading">Threading</a>, <a href="#operator">Operator</a>, <a href="#matchstatement">Match_Stmt</a>, <a href="#logging">Logging</a>, <a href="#introspection">Introspection</a>, <a href="#coroutines">Coroutines</a>],\n' +
-  '    <strong><span class="hljs-string">\'7. Libraries\'</span></strong>:   [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#consoleapp">Console_App</a>, <a href="#guiapp">GUI</a>, <a href="#scraping">Scraping</a>, <a href="#web">Web</a>, <a href="#profiling">Profile</a>],\n' +
+  '    <strong><span class="hljs-string">\'6. Advanced\'</span></strong>:    [<a href="#operator">Operator</a>, <a href="#matchstatement">Match_Stmt</a>, <a href="#logging">Logging</a>, <a href="#introspection">Introspection</a>, <a href="#threading">Threading</a>, <a href="#coroutines">Coroutines</a>],\n' +
+  '    <strong><span class="hljs-string">\'7. Libraries\'</span></strong>:   [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#consoleapp">Console_App</a>, <a href="#guiapp">GUI</a>, <a href="#scraping">Scraping</a>, <a href="#webapp">Web</a>, <a href="#profiling">Profile</a>],\n' +
   '    <strong><span class="hljs-string">\'8. Multimedia\'</span></strong>:  [<a href="#numpy">NumPy</a>, <a href="#image">Image</a>, <a href="#animation">Animation</a>, <a href="#audio">Audio</a>, <a href="#synthesizer">Synthesizer</a>, <a href="#pygame">Pygame</a>, <a href="#pandas">Pandas</a>, <a href="#plotly">Plotly</a>]\n' +
   '}\n' +
   '</code></pre>\n';
 
 const BIN_HEX =
-  '&lt;int&gt; = ±<span class="hljs-number">0b</span>&lt;bin&gt;                                  <span class="hljs-comment"># Or: ±0x&lt;hex&gt;</span>\n' +
-  '&lt;int&gt; = int(<span class="hljs-string">\'±&lt;bin&gt;\'</span>, <span class="hljs-number">2</span>)                          <span class="hljs-comment"># Or: int(\'±&lt;hex&gt;\', 16)</span>\n' +
-  '&lt;int&gt; = int(<span class="hljs-string">\'±0b&lt;bin&gt;\'</span>, <span class="hljs-number">0</span>)                        <span class="hljs-comment"># Or: int(\'±0x&lt;hex&gt;\', 0)</span>\n' +
-  '&lt;str&gt; = bin(&lt;int&gt;)                                <span class="hljs-comment"># Returns \'[-]0b&lt;bin&gt;\'. Also hex().</span>\n';
+  '&lt;int&gt; = <span class="hljs-number">0x</span>&lt;hex&gt;                                <span class="hljs-comment"># E.g. `0xFF == 255`. Also 0b&lt;bin&gt;.</span>\n' +
+  '&lt;int&gt; = int(<span class="hljs-string">\'±&lt;hex&gt;\'</span>, <span class="hljs-number">16</span>)                      <span class="hljs-comment"># Also int(\'±0x&lt;hex&gt;/±0b&lt;bin&gt;\', 0).</span>\n' +
+  '&lt;str&gt; = hex(&lt;int&gt;)                             <span class="hljs-comment"># Returns \'[-]0x&lt;hex&gt;\'. Also bin().</span>\n';
 
 const CACHE =
   '<span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> cache\n' +
@@ -55,6 +54,13 @@ const CACHE =
   '<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">fib</span><span class="hljs-params">(n)</span>:</span>\n' +
   '    <span class="hljs-keyword">return</span> n <span class="hljs-keyword">if</span> n &lt; <span class="hljs-number">2</span> <span class="hljs-keyword">else</span> fib(n-<span class="hljs-number">2</span>) + fib(n-<span class="hljs-number">1</span>)';
 
+const SPLAT =
+  '<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(*a)</span>:</span>\n' +
+  '<span class="hljs-meta">... </span>    <span class="hljs-keyword">return</span> sum(a)\n' +
+  '<span class="hljs-meta">... </span>\n' +
+  '<span class="hljs-meta">&gt;&gt;&gt; </span>add(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)\n' +
+  '<span class="hljs-number">6</span>\n';
+
 const PARAMETRIZED_DECORATOR =
   '<span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> wraps\n' +
   '\n' +
@@ -76,26 +82,20 @@ const REPR_USE_CASES =
   'print/str/repr([&lt;obj&gt;])\n' +
   'print/str/repr({&lt;obj&gt;: &lt;obj&gt;})\n' +
   '<span class="hljs-string">f\'<span class="hljs-subst">{&lt;obj&gt;!r}</span>\'</span>\n' +
-  'Z = dataclasses.make_dataclass(<span class="hljs-string">\'Z\'</span>, [<span class="hljs-string">\'a\'</span>]); print/str/repr(Z(&lt;obj&gt;))\n' +
-  '<span class="hljs-meta">&gt;&gt;&gt; </span>&lt;obj&gt;\n';
+  'Z = make_dataclass(<span class="hljs-string">\'Z\'</span>, [<span class="hljs-string">\'a\'</span>]); print/str/repr(Z(&lt;obj&gt;))\n';
 
 const CONSTRUCTOR_OVERLOADING =
   '<span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">name</span>&gt;:</span>\n' +
   '    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a=<span class="hljs-keyword">None</span>)</span>:</span>\n' +
   '        self.a = a\n';
 
-const DATACLASS =
-  '&lt;class&gt; = make_dataclass(<span class="hljs-string">\'&lt;class_name&gt;\'</span>, &lt;coll_of_attribute_names&gt;)\n' +
-  '&lt;class&gt; = make_dataclass(<span class="hljs-string">\'&lt;class_name&gt;\'</span>, &lt;coll_of_tuples&gt;)\n' +
-  '&lt;tuple&gt; = (<span class="hljs-string">\'&lt;attr_name&gt;\'</span>, &lt;type&gt; [, &lt;default_value&gt;])';
-
 const SHUTIL_COPY =
   'shutil.copy(from, to)               <span class="hljs-comment"># Copies the file. \'to\' can exist or be a dir.</span>\n' +
   'shutil.copy2(from, to)              <span class="hljs-comment"># Also copies creation and modification time.</span>\n' +
   'shutil.copytree(from, to)           <span class="hljs-comment"># Copies the directory. \'to\' must not exist.</span>\n';
 
 const OS_RENAME =
-  'os.rename(from, to)                 <span class="hljs-comment"># Renames/moves the file or directory.</span>\n' +
+  'os.rename(from, to)                 <span class="hljs-comment"># Renames or moves the file or directory \'from\'.</span>\n' +
   'os.replace(from, to)                <span class="hljs-comment"># Same, but overwrites file \'to\' even on Windows.</span>\n' +
   'shutil.move(from, to)               <span class="hljs-comment"># Rename() that moves into \'to\' if it\'s a dir.</span>\n';
 
@@ -115,19 +115,19 @@ const MATCH_EXAMPLE =
   '<span class="hljs-meta">... </span>        parts=[<span class="hljs-string">\'/\'</span>, <span class="hljs-string">\'home\'</span>, user, *_]\n' +
   '<span class="hljs-meta">... </span>    ) <span class="hljs-keyword">as</span> p <span class="hljs-keyword">if</span> p.name.lower().startswith(<span class="hljs-string">\'readme\'</span>) <span class="hljs-keyword">and</span> p.is_file():\n' +
   '<span class="hljs-meta">... </span>        print(<span class="hljs-string">f\'<span class="hljs-subst">{p.name}</span> is a readme file that belongs to user <span class="hljs-subst">{user}</span>.\'</span>)\n' +
-  '<span class="hljs-string">\'README.md is a readme file that belongs to user gto.\'</span>\n';
+  'README.md is a readme file that belongs to user gto.\n';
 
 const COROUTINES =
   '<span class="hljs-keyword">import</span> asyncio, collections, curses, curses.textpad, enum, random\n' +
   '\n' +
-  'P = collections.namedtuple(<span class="hljs-string">\'P\'</span>, <span class="hljs-string">\'x y\'</span>)    <span class="hljs-comment"># Position</span>\n' +
-  'D = enum.Enum(<span class="hljs-string">\'D\'</span>, <span class="hljs-string">\'n e s w\'</span>)             <span class="hljs-comment"># Direction</span>\n' +
-  'W, H = <span class="hljs-number">15</span>, <span class="hljs-number">7</span>                              <span class="hljs-comment"># Width, Height</span>\n' +
+  'P = collections.namedtuple(<span class="hljs-string">\'P\'</span>, <span class="hljs-string">\'x y\'</span>)     <span class="hljs-comment"># Position (x and y coordinates).</span>\n' +
+  'D = enum.Enum(<span class="hljs-string">\'D\'</span>, <span class="hljs-string">\'n e s w\'</span>)              <span class="hljs-comment"># Direction (north, east, etc.).</span>\n' +
+  'W, H = <span class="hljs-number">15</span>, <span class="hljs-number">7</span>                               <span class="hljs-comment"># Width and height constants.</span>\n' +
   '\n' +
   '<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">(screen)</span>:</span>\n' +
-  '    curses.curs_set(<span class="hljs-number">0</span>)                    <span class="hljs-comment"># Makes cursor invisible.</span>\n' +
-  '    screen.nodelay(<span class="hljs-keyword">True</span>)                  <span class="hljs-comment"># Makes getch() non-blocking.</span>\n' +
-  '    asyncio.run(main_coroutine(screen))   <span class="hljs-comment"># Starts running asyncio code.</span>\n' +
+  '    curses.curs_set(<span class="hljs-number">0</span>)                     <span class="hljs-comment"># Makes the cursor invisible.</span>\n' +
+  '    screen.nodelay(<span class="hljs-keyword">True</span>)                   <span class="hljs-comment"># Makes getch() non-blocking.</span>\n' +
+  '    asyncio.run(main_coroutine(screen))    <span class="hljs-comment"># Starts running asyncio code.</span>\n' +
   '\n' +
   '<span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main_coroutine</span><span class="hljs-params">(screen)</span>:</span>\n' +
   '    moves = asyncio.Queue()\n' +
@@ -173,7 +173,7 @@ const COROUTINES =
 const CURSES =
   '<span class="hljs-comment"># $ pip3 install windows-curses</span>\n' +
   '<span class="hljs-keyword">import</span> curses, os\n' +
-  '<span class="hljs-keyword">from</span> curses <span class="hljs-keyword">import</span> A_REVERSE, KEY_DOWN, KEY_UP, KEY_LEFT, KEY_RIGHT, KEY_ENTER\n' +
+  '<span class="hljs-keyword">from</span> curses <span class="hljs-keyword">import</span> A_REVERSE, KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT\n' +
   '\n' +
   '<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">(screen)</span>:</span>\n' +
   '    ch, first, selected, paths = <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, os.listdir()\n' +
@@ -184,10 +184,11 @@ const CURSES =
   '            color = A_REVERSE <span class="hljs-keyword">if</span> filename == paths[selected] <span class="hljs-keyword">else</span> <span class="hljs-number">0</span>\n' +
   '            screen.addnstr(y, <span class="hljs-number">0</span>, filename, width-<span class="hljs-number">1</span>, color)\n' +
   '        ch = screen.getch()\n' +
-  '        selected += (ch == KEY_DOWN) - (ch == KEY_UP)\n' +
-  '        selected = max(<span class="hljs-number">0</span>, min(len(paths)-<span class="hljs-number">1</span>, selected))\n' +
-  '        first += (selected &gt;= first + height) - (selected &lt; first)\n' +
-  '        <span class="hljs-keyword">if</span> ch <span class="hljs-keyword">in</span> [KEY_LEFT, KEY_RIGHT, KEY_ENTER, ord(<span class="hljs-string">\'\\n\'</span>), ord(<span class="hljs-string">\'\\r\'</span>)]:\n' +
+  '        selected -= (ch == KEY_UP) <span class="hljs-keyword">and</span> (selected &gt; <span class="hljs-number">0</span>)\n' +
+  '        selected += (ch == KEY_DOWN) <span class="hljs-keyword">and</span> (selected &lt; len(paths)-<span class="hljs-number">1</span>)\n' +
+  '        first -= (first &gt; selected)\n' +
+  '        first += (first &lt; selected-(height-<span class="hljs-number">1</span>))\n' +
+  '        <span class="hljs-keyword">if</span> ch <span class="hljs-keyword">in</span> [KEY_LEFT, KEY_RIGHT, ord(<span class="hljs-string">\'\\n\'</span>)]:\n' +
   '            new_dir = <span class="hljs-string">\'..\'</span> <span class="hljs-keyword">if</span> ch == KEY_LEFT <span class="hljs-keyword">else</span> paths[selected]\n' +
   '            <span class="hljs-keyword">if</span> os.path.isdir(new_dir):\n' +
   '                os.chdir(new_dir)\n' +
@@ -220,8 +221,8 @@ const AUDIO_1 =
   '<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_wav_file</span><span class="hljs-params">(filename, samples_f, p=<span class="hljs-keyword">None</span>, nchannels=<span class="hljs-number">1</span>, sampwidth=<span class="hljs-number">2</span>, framerate=<span class="hljs-number">44100</span>)</span>:</span>\n' +
   '    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_bytes</span><span class="hljs-params">(a_float)</span>:</span>\n' +
   '        a_float = max(<span class="hljs-number">-1</span>, min(<span class="hljs-number">1</span> - <span class="hljs-number">2e-16</span>, a_float))\n' +
-  '        a_float += p.sampwidth == <span class="hljs-number">1</span>\n' +
-  '        a_float *= pow(<span class="hljs-number">2</span>, p.sampwidth * <span class="hljs-number">8</span> - <span class="hljs-number">1</span>)\n' +
+  '        a_float += (p.sampwidth == <span class="hljs-number">1</span>)\n' +
+  '        a_float *= pow(<span class="hljs-number">2</span>, (p.sampwidth * <span class="hljs-number">8</span>) - <span class="hljs-number">1</span>)\n' +
   '        <span class="hljs-keyword">return</span> int(a_float).to_bytes(p.sampwidth, <span class="hljs-string">\'little\'</span>, signed=(p.sampwidth != <span class="hljs-number">1</span>))\n' +
   '    <span class="hljs-keyword">if</span> p <span class="hljs-keyword">is</span> <span class="hljs-keyword">None</span>:\n' +
   '        p = wave._wave_params(nchannels, sampwidth, framerate, <span class="hljs-number">0</span>, <span class="hljs-string">\'NONE\'</span>, <span class="hljs-string">\'not compressed\'</span>)\n' +
@@ -264,19 +265,19 @@ const MARIO =
   '<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">run</span><span class="hljs-params">(screen, images, mario, tiles)</span>:</span>\n' +
   '    clock = pg.time.Clock()\n' +
   '    pressed = set()\n' +
-  '    <span class="hljs-keyword">while</span> <span class="hljs-keyword">not</span> pg.event.get(pg.QUIT) <span class="hljs-keyword">and</span> clock.tick(<span class="hljs-number">28</span>):\n' +
-  '        keys = {pg.K_UP: D.n, pg.K_RIGHT: D.e, pg.K_DOWN: D.s, pg.K_LEFT: D.w}\n' +
-  '        pressed |= {keys.get(e.key) <span class="hljs-keyword">for</span> e <span class="hljs-keyword">in</span> pg.event.get(pg.KEYDOWN)}\n' +
-  '        pressed -= {keys.get(e.key) <span class="hljs-keyword">for</span> e <span class="hljs-keyword">in</span> pg.event.get(pg.KEYUP)}\n' +
+  '    <span class="hljs-keyword">while</span> <span class="hljs-keyword">not</span> pg.event.get(pg.QUIT):\n' +
+  '        clock.tick(<span class="hljs-number">28</span>)\n' +
+  '        pressed |= {e.key <span class="hljs-keyword">for</span> e <span class="hljs-keyword">in</span> pg.event.get(pg.KEYDOWN)}\n' +
+  '        pressed -= {e.key <span class="hljs-keyword">for</span> e <span class="hljs-keyword">in</span> pg.event.get(pg.KEYUP)}\n' +
   '        update_speed(mario, tiles, pressed)\n' +
   '        update_position(mario, tiles)\n' +
   '        draw(screen, images, mario, tiles)\n' +
   '\n' +
   '<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">update_speed</span><span class="hljs-params">(mario, tiles, pressed)</span>:</span>\n' +
   '    x, y = mario.spd\n' +
-  '    x += <span class="hljs-number">2</span> * ((D.e <span class="hljs-keyword">in</span> pressed) - (D.w <span class="hljs-keyword">in</span> pressed))\n' +
+  '    x += <span class="hljs-number">2</span> * ((pg.K_RIGHT <span class="hljs-keyword">in</span> pressed) - (pg.K_LEFT <span class="hljs-keyword">in</span> pressed))\n' +
   '    x += (x &lt; <span class="hljs-number">0</span>) - (x &gt; <span class="hljs-number">0</span>)\n' +
-  '    y += <span class="hljs-number">1</span> <span class="hljs-keyword">if</span> D.s <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> get_boundaries(mario.rect, tiles) <span class="hljs-keyword">else</span> (D.n <span class="hljs-keyword">in</span> pressed) * <span class="hljs-number">-10</span>\n' +
+  '    y += <span class="hljs-number">1</span> <span class="hljs-keyword">if</span> D.s <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> get_boundaries(mario.rect, tiles) <span class="hljs-keyword">else</span> (pg.K_UP <span class="hljs-keyword">in</span> pressed) * <span class="hljs-number">-10</span>\n' +
   '    mario.spd = P(x=max(-MAX_S.x, min(MAX_S.x, x)), y=max(-MAX_S.y, min(MAX_S.y, y)))\n' +
   '\n' +
   '<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">update_position</span><span class="hljs-params">(mario, tiles)</span>:</span>\n' +
@@ -299,7 +300,7 @@ const MARIO =
   '    screen.fill((<span class="hljs-number">85</span>, <span class="hljs-number">168</span>, <span class="hljs-number">255</span>))\n' +
   '    mario.facing_left = mario.spd.x &lt; <span class="hljs-number">0</span> <span class="hljs-keyword">if</span> mario.spd.x <span class="hljs-keyword">else</span> mario.facing_left\n' +
   '    is_airborne = D.s <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> get_boundaries(mario.rect, tiles)\n' +
-  '    image_index = <span class="hljs-number">4</span> <span class="hljs-keyword">if</span> is_airborne <span class="hljs-keyword">else</span> (next(mario.frame_cycle) <span class="hljs-keyword">if</span> mario.spd.x <span class="hljs-keyword">else</span> <span class="hljs-number">6</span>)\n' +
+  '    image_index = <span class="hljs-number">4</span> <span class="hljs-keyword">if</span> is_airborne <span class="hljs-keyword">else</span> next(mario.frame_cycle) <span class="hljs-keyword">if</span> mario.spd.x <span class="hljs-keyword">else</span> <span class="hljs-number">6</span>\n' +
   '    screen.blit(images[image_index + (mario.facing_left * <span class="hljs-number">9</span>)], mario.rect)\n' +
   '    <span class="hljs-keyword">for</span> t <span class="hljs-keyword">in</span> tiles:\n' +
   '        is_border = t.x <span class="hljs-keyword">in</span> [<span class="hljs-number">0</span>, (W-<span class="hljs-number">1</span>)*<span class="hljs-number">16</span>] <span class="hljs-keyword">or</span> t.y <span class="hljs-keyword">in</span> [<span class="hljs-number">0</span>, (H-<span class="hljs-number">1</span>)*<span class="hljs-number">16</span>]\n' +
@@ -323,26 +324,25 @@ const GROUPBY =
   '<span class="hljs-number">3</span>   <span class="hljs-number">1</span>   <span class="hljs-number">2</span>\n' +
   '<span class="hljs-number">6</span>  <span class="hljs-number">11</span>  <span class="hljs-number">13</span>';
 
-
 const CYTHON_1 =
-  '<span class="hljs-keyword">cdef</span> &lt;ctype&gt; &lt;var_name&gt; = &lt;obj&gt;\n' +
-  '<span class="hljs-keyword">cdef</span> &lt;ctype&gt;[n_elements] &lt;var_name&gt; = [&lt;el_1&gt;, &lt;el_2&gt;, ...]\n' +
-  '<span class="hljs-keyword">cdef</span> &lt;ctype/void&gt; &lt;func_name&gt;(&lt;ctype&gt; &lt;arg_name&gt;): ...\n';
+  '<span class="hljs-keyword">cdef</span> &lt;type&gt; &lt;var_name&gt; [= &lt;obj/var&gt;]                 <span class="hljs-comment"># Either Python or C type variable.</span>\n' +
+  '<span class="hljs-keyword">cdef</span> &lt;ctype&gt; *&lt;pointer_name&gt; [= &amp;&lt;var&gt;]              <span class="hljs-comment"># Use &lt;pointer&gt;[0] to get the value.</span>\n' +
+  '<span class="hljs-keyword">cdef</span> &lt;ctype&gt;[size] &lt;array_name&gt; [= &lt;coll/array&gt;]     <span class="hljs-comment"># Also `&lt;ctype&gt;[:] &lt;mview&gt; = &lt;array&gt;`.</span>\n' +
+  '<span class="hljs-keyword">cdef</span> &lt;ctype&gt; *&lt;array_name&gt; [= &lt;coll/array/pointer&gt;]  <span class="hljs-comment"># E.g. `&lt;&lt;ctype&gt; *&gt; malloc(n_bytes)`.</span>\n';
 
 const CYTHON_2 =
-  '<span class="hljs-keyword">cdef</span> <span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">class_name</span>&gt;:</span>\n' +
-  '    <span class="hljs-keyword">cdef</span> <span class="hljs-keyword">public</span> &lt;ctype&gt; &lt;attr_name&gt;\n' +
-  '    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, &lt;ctype&gt; &lt;arg_name&gt;)</span>:</span>\n' +
-  '        self.&lt;attr_name&gt; = &lt;arg_name&gt;\n';
+  '<span class="hljs-keyword">cdef</span> &lt;type&gt; &lt;func_name&gt;(&lt;type&gt; [*]&lt;arg_name&gt;): ...   <span class="hljs-comment"># Omitted types default to `object`.</span>\n';
 
 const CYTHON_3 =
-  '<span class="hljs-keyword">cdef</span> <span class="hljs-keyword">enum</span> &lt;enum_name&gt;: &lt;member_name&gt;, &lt;member_name&gt;, ...\n';
+  '<span class="hljs-keyword">cdef</span> <span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">class_name</span>&gt;:</span>                             <span class="hljs-comment"># Also `cdef struct &lt;struct_name&gt;:`.</span>\n' +
+  '    <span class="hljs-keyword">cdef</span> <span class="hljs-keyword">public</span> &lt;type&gt; [*]&lt;attr_name&gt;                <span class="hljs-comment"># Also `... &lt;ctype&gt; [*]&lt;field_name&gt;`.</span>\n' +
+  '    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, &lt;type&gt; &lt;arg_name&gt;)</span>:</span>           <span class="hljs-comment"># Also `cdef __dealloc__(self):`.</span>\n' +
+  '        self.&lt;attr_name&gt; = &lt;arg_name&gt;                <span class="hljs-comment"># Also `... free(&lt;array/pointer&gt;)`.</span>\n';
 
 const INDEX =
-  '<li><strong>Only available in the <a href="https://transactions.sendowl.com/products/78175486/4422834F/view">PDF</a>.</strong></li>\n' +
   '<li><strong>Ctrl+F / ⌘F is usually sufficient.</strong></li>\n' +
   '<li><strong>Searching <code class="python hljs"><span class="hljs-string">\'#&lt;title&gt;\'</span></code> will limit the search to the titles.</strong></li>\n' +
-  '<li><strong>Click on the <code class="python hljs"><span class="hljs-string">\'#\'</span></code> symbol to get a link to specific section.</strong></li>\n';
+  '<li><strong>Click on the title\'s <code class="python hljs"><span class="hljs-string">\'#\'</span></code> to get a link to its section.</strong></li>\n';
 
 
 const DIAGRAM_1_A =
@@ -424,6 +424,18 @@ const DIAGRAM_5_A =
   "|              |  {<float>:.2}  |  {<float>:.2f} |  {<float>:.2e} |  {<float>:.2%} |\n" +
   "+--------------+----------------+----------------+----------------+----------------+\n";
 
+const DIAGRAM_55_A =
+  "+---------------------------+--------------+--------------+----------------+\n";
+
+const DIAGRAM_55_B =
+  '┏━━━━━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┓\n' +
+  '┃                           │  func(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>)  │ func(<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>) │ func(x=<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>) ┃\n' +
+  '┠───────────────────────────┼──────────────┼──────────────┼────────────────┨\n' +
+  '┃ <span class="hljs-title">func</span>(x, *args, **kwargs): │      ✓       │      ✓       │       ✓        ┃\n' +
+  '┃ <span class="hljs-title">func</span>(*args, y, **kwargs): │              │      ✓       │       ✓        ┃\n' +
+  '┃ <span class="hljs-title">func</span>(*, x, **kwargs):     │              │              │       ✓        ┃\n' +
+  '┗━━━━━━━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┛\n';
+
 const DIAGRAM_6_A =
   '+------------+------------+------------+------------+--------------+\n' +
   '|            |  Iterable  | Collection |  Sequence  | abc.Sequence |\n' +
@@ -448,25 +460,25 @@ const DIAGRAM_7_A =
 
 const DIAGRAM_7_B =
   "BaseException\n" +
-  " ├── SystemExit                   <span class='hljs-comment'># Raised by the sys.exit() function.</span>\n" +
-  " ├── KeyboardInterrupt            <span class='hljs-comment'># Raised when the user hits the interrupt key (ctrl-c).</span>\n" +
+  " ├── SystemExit                   <span class='hljs-comment'># Raised by the sys.exit() function (see #Exit for details).</span>\n" +
+  " ├── KeyboardInterrupt            <span class='hljs-comment'># Raised when the user hits the interrupt key (control-c).</span>\n" +
   " └── Exception                    <span class='hljs-comment'># User-defined exceptions should be derived from this class.</span>\n" +
   "      ├── ArithmeticError         <span class='hljs-comment'># Base class for arithmetic errors such as ZeroDivisionError.</span>\n" +
   "      ├── AssertionError          <span class='hljs-comment'># Raised by `assert &lt;exp&gt;` if expression returns false value.</span>\n" +
   "      ├── AttributeError          <span class='hljs-comment'># Raised when object doesn't have requested attribute/method.</span>\n" +
   "      ├── EOFError                <span class='hljs-comment'># Raised by input() when it hits an end-of-file condition.</span>\n" +
   "      ├── LookupError             <span class='hljs-comment'># Base class for errors when a collection can't find an item.</span>\n" +
-  "      │    ├── IndexError         <span class='hljs-comment'># Raised when a sequence index is out of range.</span>\n" +
+  "      │    ├── IndexError         <span class='hljs-comment'># Raised when index of a sequence (list/str) is out of range.</span>\n" +
   "      │    └── KeyError           <span class='hljs-comment'># Raised when a dictionary key or set element is missing.</span>\n" +
   "      ├── MemoryError             <span class='hljs-comment'># Out of memory. May be too late to start deleting variables.</span>\n" +
   "      ├── NameError               <span class='hljs-comment'># Raised when nonexistent name (variable/func/class) is used.</span>\n" +
   "      │    └── UnboundLocalError  <span class='hljs-comment'># Raised when local name is used before it's being defined.</span>\n" +
-  "      ├── OSError                 <span class='hljs-comment'># Errors such as FileExistsError/TimeoutError (see #Open).</span>\n" +
-  "      │    └── ConnectionError    <span class='hljs-comment'># Errors such as BrokenPipeError/ConnectionAbortedError.</span>\n" +
+  "      ├── OSError                 <span class='hljs-comment'># Errors such as FileExistsError, TimeoutError (see #Open).</span>\n" +
+  "      │    └── ConnectionError    <span class='hljs-comment'># Errors such as BrokenPipeError and ConnectionAbortedError.</span>\n" +
   "      ├── RuntimeError            <span class='hljs-comment'># Raised by errors that don't fall into other categories.</span>\n" +
   "      │    ├── NotImplementedEr…  <span class='hljs-comment'># Can be raised by abstract methods or by unfinished code.</span>\n" +
-  "      │    └── RecursionError     <span class='hljs-comment'># Raised when the maximum recursion depth is exceeded.</span>\n" +
-  "      ├── StopIteration           <span class='hljs-comment'># Raised when an empty iterator is passed to next().</span>\n" +
+  "      │    └── RecursionError     <span class='hljs-comment'># Raised if max recursion depth is exceeded (3k by default).</span>\n" +
+  "      ├── StopIteration           <span class='hljs-comment'># Raised when exhausted (empty) iterator is passed to next().</span>\n" +
   "      ├── TypeError               <span class='hljs-comment'># When an argument of the wrong type is passed to function.</span>\n" +
   "      └── ValueError              <span class='hljs-comment'># When argument has the right type but inappropriate value.</span>\n";
 
@@ -600,60 +612,126 @@ const DIAGRAM_13_B =
   "┃              │    y  2.0   │   y   2.0   │      y  2.0   ┃\n" +
   "┗━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n";
 
+const DIAGRAM_13_BB =
+  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓\n" +
+  "┃                │    'mean'   │   ['mean']  │ {'m': 'mean'} ┃\n" +
+  "┠────────────────┼─────────────┼─────────────┼───────────────┨\n" +
+  "┃ s.apply/agg(…) │     1.5     │  mean  1.5  │     m  1.5    ┃\n" +
+  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n" +
+  "\n" +
+  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓\n" +
+  "┃                │    'rank'   │   ['rank']  │ {'r': 'rank'} ┃\n" +
+  "┠────────────────┼─────────────┼─────────────┼───────────────┨\n" +
+  "┃ s.apply/agg(…) │             │      rank   │               ┃\n" +
+  "┃                │    x  1.0   │   x   1.0   │   r  x  1.0   ┃\n" +
+  "┃                │    y  2.0   │   y   2.0   │      y  2.0   ┃\n" +
+  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n";
+
+const DIAGRAM_13_XXX =
+  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━┓\n" +
+  "┃                │   'sum'   │ ['sum', 'max'] │   'rank'  │ ['rank', 'diff'] ┃\n" +
+  "┠────────────────┼───────────┼────────────────┼───────────┼──────────────────┨\n" +
+  "┃ s.apply/agg(…) │     3     │    sum    3    │  x  1.0   │     rank  diff   ┃\n" +
+  "┃                │           │    max    2    │  y  2.0   │  x   1.0   NaN   ┃\n" +
+  "┃                │           │    Name: a     │  Name: a  │  y   2.0   1.0   ┃\n" +
+  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━┛\n";
+
+const DIAGRAM_13_XX =
+  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┓\n" +
+  "┃                │   'sum'   │   'rank'  │ ['sum', 'max'] ┃\n" +
+  "┠────────────────┼───────────┼───────────┼────────────────┨\n" +
+  "┃ s.apply/agg(…) │     3     │  x  1.0   │    sum    3    ┃\n" +
+  "┃                │           │  y  2.0   │    max    2    ┃\n" +
+  "┃                │           │  Name: a  │    Name: a     ┃\n" +
+  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┛\n";
+
+const DIAGRAM_13_X =
+  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━┓\n" +
+  "┃                │   'sum'   │   'rank'  │ ['sum', 'max'] │ ['rank', 'diff'] ┃\n" +
+  "┠────────────────┼───────────┼───────────┼────────────────┼──────────────────┨\n" +
+  "┃ s.apply/agg(…) │     3     │  x  1.0   │    sum    3    │     rank  diff   ┃\n" +
+  "┃                │           │  y  2.0   │    max    2    │  x   1.0   NaN   ┃\n" +
+  "┃                │           │  Name: a  │    Name: a     │  y   2.0   1.0   ┃\n" +
+  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━┛\n";
+
+const DIAGRAM_13_Y =
+  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━━━━┓\n" +
+  "┃                │   'sum'   │   'rank'  │  ['sum']  │ ['rank']  ┃\n" +
+  "┠────────────────┼───────────┼───────────┼───────────┼───────────┨\n" +
+  "┃ s.apply/agg(…) │     3     │  x  1.0   │  sum 3    │     rank  ┃\n" +
+  "┃                │           │  y  2.0   │  Name: a  │  x   1.0  ┃\n" +
+  "┃                │           │  Name: a  │           │  y   2.0  ┃\n" +
+  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━━━━┛\n";
+
+const DIAGRAM_13_BBB =
+  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓\n" +
+  "┃                │    'sum'    │   ['sum']   │ {'s': 'sum'}  ┃\n" +
+  "┠────────────────┼─────────────┼─────────────┼───────────────┨\n" +
+  "┃ s.apply/agg(…) │      3      │    sum  3   │     s  3      ┃\n" +
+  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n" +
+  "\n" +
+  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓\n" +
+  "┃                │    'rank'   │   ['rank']  │ {'r': 'rank'} ┃\n" +
+  "┠────────────────┼─────────────┼─────────────┼───────────────┨\n" +
+  "┃ s.apply/agg(…) │             │      rank   │               ┃\n" +
+  "┃                │    x  1.0   │   x   1.0   │   r  x  1.0   ┃\n" +
+  "┃                │    y  2.0   │   y   2.0   │      y  2.0   ┃\n" +
+  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n";
+
 const DIAGRAM_14_A =
   "|              |    'rank'   |   ['rank']  | {'r': 'rank'} |";
 
 const DIAGRAM_15_A =
-  '+------------------------+---------------+------------+------------+--------------------------+';
+  '+-----------------------+---------------+------------+------------+---------------------------+';
 
 const DIAGRAM_15_B =
-  "┏━━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━┓\n" +
-  "┃                        │    'outer'    │   'inner'  │   'left'   │       Description        ┃\n" +
-  "┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨\n" +
-  "┃ l.merge(r, on='y',     │    x   y   z  │ x   y   z  │ x   y   z  │ Merges on column if 'on' ┃\n" +
-  "┃            how=…)      │ 0  1   2   .  │ 3   4   5  │ 1   2   .  │ or 'left/right_on' are   ┃\n" +
-  "┃                        │ 1  3   4   5  │            │ 3   4   5  │ set, else on shared cols.┃\n" +
-  "┃                        │ 2  .   6   7  │            │            │ Uses 'inner' by default. ┃\n" +
-  "┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨\n" +
-  "┃ l.join(r, lsuffix='l', │    x yl yr  z │            │ x yl yr  z │ Merges on row keys.      ┃\n" +
-  "┃           rsuffix='r', │ a  1  2  .  . │ x yl yr  z │ 1  2  .  . │ Uses 'left' by default.  ┃\n" +
-  "┃           how=…)       │ b  3  4  4  5 │ 3  4  4  5 │ 3  4  4  5 │ If r is a Series, it is  ┃\n" +
-  "┃                        │ c  .  .  6  7 │            │            │ treated as a column.     ┃\n" +
-  "┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨\n" +
-  "┃ pd.concat([l, r],      │    x   y   z  │     y      │            │ Adds rows at the bottom. ┃\n" +
-  "┃           axis=0,      │ a  1   2   .  │     2      │            │ Uses 'outer' by default. ┃\n" +
-  "┃           join=…)      │ b  3   4   .  │     4      │            │ A Series is treated as a ┃\n" +
-  "┃                        │ b  .   4   5  │     4      │            │ column. To add a row use ┃\n" +
-  "┃                        │ c  .   6   7  │     6      │            │ pd.concat([l, DF([s])]). ┃\n" +
-  "┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨\n" +
-  "┃ pd.concat([l, r],      │    x  y  y  z │            │            │ Adds columns at the      ┃\n" +
-  "┃           axis=1,      │ a  1  2  .  . │ x  y  y  z │            │ right end. Uses 'outer'  ┃\n" +
-  "┃           join=…)      │ b  3  4  4  5 │ 3  4  4  5 │            │ by default. A Series is  ┃\n" +
-  "┃                        │ c  .  .  6  7 │            │            │ treated as a column.     ┃\n" +
-  "┗━━━━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━━━━━━━━┛\n";
+  "┏━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━━┓\n" +
+  "┃                       │    'outer'    │   'inner'  │   'left'   │       Description         ┃\n" +
+  "┠───────────────────────┼───────────────┼────────────┼────────────┼───────────────────────────┨\n" +
+  "┃ df.merge(df_2,        │    x   y   z  │ x   y   z  │ x   y   z  │ Merges on column if 'on'  ┃\n" +
+  "┃          on='y',      │ 0  1   2   .  │ 3   4   5  │ 1   2   .  │ or 'left_on/right_on' are ┃\n" +
+  "┃          how=…)       │ 1  3   4   5  │            │ 3   4   5  │ set, else on shared cols. ┃\n" +
+  "┃                       │ 2  .   6   7  │            │            │ Uses 'inner' by default.  ┃\n" +
+  "┠───────────────────────┼───────────────┼────────────┼────────────┼───────────────────────────┨\n" +
+  "┃ df.join(df_2,         │    x yl yr  z │            │ x yl yr  z │ Merges on row keys.       ┃\n" +
+  "┃         lsuffix='l',  │ a  1  2  .  . │ x yl yr  z │ 1  2  .  . │ Uses 'left' by default.   ┃\n" +
+  "┃         rsuffix='r',  │ b  3  4  4  5 │ 3  4  4  5 │ 3  4  4  5 │ If Series is passed, it   ┃\n" +
+  "┃         how=…)        │ c  .  .  6  7 │            │            │ is treated as a column.   ┃\n" +
+  "┠───────────────────────┼───────────────┼────────────┼────────────┼───────────────────────────┨\n" +
+  "┃ pd.concat([df, df_2], │    x   y   z  │     y      │            │ Adds rows at the bottom.  ┃\n" +
+  "┃           axis=0,     │ a  1   2   .  │     2      │            │ Uses 'outer' by default.  ┃\n" +
+  "┃           join=…)     │ b  3   4   .  │     4      │            │ A Series is treated as a  ┃\n" +
+  "┃                       │ b  .   4   5  │     4      │            │ column. To add a row use  ┃\n" +
+  "┃                       │ c  .   6   7  │     6      │            │ pd.concat([df, DF([s])]). ┃\n" +
+  "┠───────────────────────┼───────────────┼────────────┼────────────┼───────────────────────────┨\n" +
+  "┃ pd.concat([df, df_2], │    x  y  y  z │            │            │ Adds columns at the       ┃\n" +
+  "┃           axis=1,     │ a  1  2  .  . │ x  y  y  z │            │ right end. Uses 'outer'   ┃\n" +
+  "┃           join=…)     │ b  3  4  4  5 │ 3  4  4  5 │            │ by default. A Series is   ┃\n" +
+  "┃                       │ c  .  .  6  7 │            │            │ treated as a column.      ┃\n" +
+  "┗━━━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━━━━━━━━━┛\n";
 
 const DIAGRAM_16_A =
-  '| l.apply(…)     |      x  4     |        x  y   |     x  4      |';
+  '| df.apply(…)     |      x  4     |        x  y   |     x  4      |';
 
 const DIAGRAM_16_B =
-  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓\n" +
-  "┃                │     'sum'     │    ['sum']    │ {'x': 'sum'}  ┃\n" +
-  "┠────────────────┼───────────────┼───────────────┼───────────────┨\n" +
-  "┃ l.apply(…)     │      x  4     │        x  y   │     x  4      ┃\n" +
-  "┃ l.agg(…)       │      y  6     │   sum  4  6   │               ┃\n" +
-  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n" +
+  "┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓\n" +
+  "┃                 │     'sum'     │    ['sum']    │ {'x': 'sum'}  ┃\n" +
+  "┠─────────────────┼───────────────┼───────────────┼───────────────┨\n" +
+  "┃ df.apply(…)     │      x  4     │        x  y   │     x  4      ┃\n" +
+  "┃ df.agg(…)       │      y  6     │   sum  4  6   │               ┃\n" +
+  "┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n" +
   "\n" +
-  "┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓\n" +
-  "┃                │     'rank'    │    ['rank']   │ {'x': 'rank'} ┃\n" +
-  "┠────────────────┼───────────────┼───────────────┼───────────────┨\n" +
-  "┃ l.apply(…)     │               │       x    y  │               ┃\n" +
-  "┃ l.agg(…)       │       x    y  │    rank rank  │         x     ┃\n" +
-  "┃ l.transform(…) │  a  1.0  1.0  │  a  1.0  1.0  │    a  1.0     ┃\n" +
-  "┃                │  b  2.0  2.0  │  b  2.0  2.0  │    b  2.0     ┃\n" +
-  "┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n";
+  "┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓\n" +
+  "┃                 │     'rank'    │    ['rank']   │ {'x': 'rank'} ┃\n" +
+  "┠─────────────────┼───────────────┼───────────────┼───────────────┨\n" +
+  "┃ df.apply(…)     │               │       x    y  │               ┃\n" +
+  "┃ df.agg(…)       │       x    y  │    rank rank  │         x     ┃\n" +
+  "┃ df.transform(…) │  a  1.0  1.0  │  a  1.0  1.0  │    a  1.0     ┃\n" +
+  "┃                 │  b  2.0  2.0  │  b  2.0  2.0  │    b  2.0     ┃\n" +
+  "┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n";
 
 const DIAGRAM_17_A =
-  "|                |     'rank'    |    ['rank']   | {'x': 'rank'} |";
+  "|                 |     'rank'    |    ['rank']   | {'x': 'rank'} |";
 
 const DIAGRAM_18_A =
   '| gb.agg(…)       |      x   y  |             |      x    y |               |';
@@ -674,23 +752,33 @@ const DIAGRAM_18_B =
   "┃                 │  c  11  13  │   c  2  2   │             │               ┃\n" +
   "┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛\n";
 
-const MENU = '<a href="https://raw.githubusercontent.com/gto76/python-cheatsheet/main/README.md">Download text file</a>, <a href="https://transactions.sendowl.com/products/78175486/4422834F/view">Buy PDF</a>, <a href="https://github.com/gto76/python-cheatsheet">Fork me on GitHub</a>, <a href="https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions">Check out FAQ</a> or <a href="index.html?theme=dark3">Switch to dark theme</a>.\n';
+const MENU = '<a href="https://raw.githubusercontent.com/gto76/python-cheatsheet/main/README.md">Download text file</a>, <a href="https://github.com/gto76/python-cheatsheet">Fork me on GitHub</a>, <a href="https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions">Check out FAQ</a> or <a href="index.html?theme=dark3">Switch to dark theme</a>.\n';
 
 const DARK_THEME_SCRIPT =
   '<script>\n' +
-  '  // Changes the image and link to theme if URL ends with "index.html?theme=dark". \n' +
-  '  if (window.location.search.search(/[?&]theme=dark/) !== -1) {\n' +
+  '  // Changes the banner image and link-to-theme if "theme=dark" is in query string\n' +
+  '  // or if browser prefers dark mode and theme is not explicitly set.\n' +
   '\n' +
+  'const theme_not_set_in_query = window.location.search.search(/[?&]theme=light/) == -1\n' +
+  'const browser_prefers_dark = window.matchMedia(\'(prefers-color-scheme: dark)\').matches;\n' +
+  '\n' +
+  '  if ((window.location.search.search(/[?&]theme=dark/) !== -1) || \n' +
+  '      (theme_not_set_in_query && browser_prefers_dark)) {\n' +
+  '    activateDarkMode();\n' +
+  '  }\n' +
+  '\n' +
+  '  function activateDarkMode() {\n' +
   '    var link_to_theme = document.createElement("a")\n' +
-  '    link_to_theme.href = "index.html"\n' +
+  '    link_to_theme.href = "index.html?theme=light"\n' +
   '    link_to_theme.text = "Switch to light theme"\n' +
-  '    document.getElementsByClassName("banner")[0].firstChild.children[4].replaceWith(link_to_theme)\n' +
+  '    document.getElementsByClassName("banner")[0].firstChild.children[3].replaceWith(link_to_theme)\n' +
   '\n' +
   '    var img_dark = document.createElement("img");\n' +
   '    img_dark.src = "web/image_orig_blue6.png";\n' +
   '    img_dark.alt = "Monthy Python";\n' +
   '    if ((window.location.search.search(/[?&]theme=dark2/) !== -1) ||\n' +
-  '        (window.location.search.search(/[?&]theme=dark3/) !== -1)) {\n' +
+  '        (window.location.search.search(/[?&]theme=dark3/) !== -1) ||\n' +
+  '        (theme_not_set_in_query && browser_prefers_dark)) {\n' +
   '      img_dark.style = "width: 910px;";\n' +
   '    } else {\n' +
   '      img_dark.style = "width: 960px;";\n' +
@@ -783,16 +871,14 @@ function unindentBanner() {
 function updateDiagrams() {
   $(`code:contains(${DIAGRAM_1_A})`).html(DIAGRAM_1_B);
   $(`code:contains(${DIAGRAM_2_A})`).html(DIAGRAM_2_B);
-  $(`code:contains(${DIAGRAM_3_A})`).html(DIAGRAM_3_B);
   $(`code:contains(${DIAGRAM_4_A})`).html(DIAGRAM_4_B);
   $(`code:contains(${DIAGRAM_5_A})`).parent().remove();
+  $(`code:contains(${DIAGRAM_55_A})`).html(DIAGRAM_55_B);
   $(`code:contains(${DIAGRAM_6_A})`).html(DIAGRAM_6_B);
   $(`code:contains(${DIAGRAM_7_A})`).html(DIAGRAM_7_B);
   $(`code:contains(${DIAGRAM_8_A})`).html(DIAGRAM_8_B);
   $(`code:contains(${DIAGRAM_9_A})`).html(DIAGRAM_9_B);
   $(`code:contains(${DIAGRAM_95_A})`).html(DIAGRAM_95_B);
-  $(`code:contains(${DIAGRAM_10_A})`).html(DIAGRAM_10_B);
-  $(`code:contains(${DIAGRAM_11_A})`).html(DIAGRAM_11_B);
   $(`code:contains(${DIAGRAM_115_A})`).html(DIAGRAM_115_B);
   $(`code:contains(${DIAGRAM_12_A})`).html(DIAGRAM_12_B).removeClass("text").removeClass("language-text").addClass("python");
   $(`code:contains(${DIAGRAM_13_A})`).html(DIAGRAM_13_B).removeClass("text").removeClass("language-text").addClass("python");
@@ -800,7 +886,6 @@ function updateDiagrams() {
   $(`code:contains(${DIAGRAM_15_A})`).html(DIAGRAM_15_B).removeClass("text").removeClass("language-text").addClass("python");
   $(`code:contains(${DIAGRAM_16_A})`).html(DIAGRAM_16_B).removeClass("text").removeClass("language-text").addClass("python");
   $(`code:contains(${DIAGRAM_17_A})`).parent().remove();
-  $(`code:contains(${DIAGRAM_18_A})`).html(DIAGRAM_18_B).removeClass("text").removeClass("language-text").addClass("python");
 }
 
 function highlightCode() {
@@ -837,29 +922,28 @@ function fixClasses() {
 }
 
 function fixHighlights() {
-  $(`code:contains(<int> = ±0b<bin>)`).html(BIN_HEX);
+  $(`code:contains(<int> = 0x<hex>)`).html(BIN_HEX);
   $(`code:contains( + fib(n)`).html(CACHE);
+  $(`code:contains(>>> def add)`).html(SPLAT);
   $(`code:contains(@debug(print_result=True))`).html(PARAMETRIZED_DECORATOR);
   $(`code:contains(print/str/repr([<obj>]))`).html(REPR_USE_CASES);
-  $(`code:contains((self, a=None):)`).html(CONSTRUCTOR_OVERLOADING);
-  $(`code:contains(make_dataclass(\'<class_name>\')`).html(DATACLASS);
   $(`code:contains(shutil.copy)`).html(SHUTIL_COPY);
   $(`code:contains(os.rename)`).html(OS_RENAME);
   $(`code:contains(\'<n>s\')`).html(STRUCT_FORMAT);
   $(`code:contains(match <object/expression>:)`).html(MATCH);
   $(`code:contains(>>> match Path)`).html(MATCH_EXAMPLE);
+  $(`code:contains(>>> log.basicConfig()`).html(LOGGING_EXAMPLE);
   $(`code:contains(import asyncio, collections, curses, curses.textpad, enum, random)`).html(COROUTINES);
-  $(`code:contains(import curses, os)`).html(CURSES);
   $(`code:contains(pip3 install tqdm)`).html(PROGRESS_BAR);
-  $(`code:contains(>>> log.basicConfig()`).html(LOGGING_EXAMPLE);
+  $(`code:contains(import curses, os)`).html(CURSES);
   $(`code:contains(a_float = max()`).html(AUDIO_1);
   $(`code:contains(samples_f = (sin(i *)`).html(AUDIO_2);
   $(`code:contains(collections, dataclasses, enum, io, itertools)`).html(MARIO);
   $(`code:contains(>>> gb = df.groupby)`).html(GROUPBY);
-  $(`code:contains(cdef <ctype> <var_name> = <obj>)`).html(CYTHON_1);
-  $(`code:contains(cdef class <class_name>:)`).html(CYTHON_2);
-  $(`code:contains(cdef enum <enum_name>: <member_name>, <member_name>, ...)`).html(CYTHON_3);
-  $(`ul:contains(Only available in)`).html(INDEX);
+  $(`code:contains(cdef <type> <var_name> [= <obj/var>])`).html(CYTHON_1);
+  $(`code:contains(cdef <type> <func_name>(<type> [*]<arg_name>): ...)`).html(CYTHON_2);
+  $(`code:contains(cdef class <class_name>:)`).html(CYTHON_3);
+  $(`ul:contains(Ctrl+F / ⌘F is usually sufficient.)`).html(INDEX);
 }
 
 function preventPageBreaks() {
@@ -903,7 +987,7 @@ function insertPageBreakBefore(an_id) {
 }
 
 function fixPandasDiagram() {
-  const diagram_15 = '┏━━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━┓';
+  const diagram_15 = '┏━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━━┓';
   $(`code:contains(${diagram_15})`).find(".hljs-keyword:contains(and)").after("and");
   $(`code:contains(${diagram_15})`).find(".hljs-keyword:contains(as)").after("as");
   $(`code:contains(${diagram_15})`).find(".hljs-keyword:contains(is)").after("is");
@@ -911,6 +995,10 @@ function fixPandasDiagram() {
   $(`code:contains(${diagram_15})`).find(".hljs-keyword:contains(or)").after("or");
   $(`code:contains(${diagram_15})`).find(".hljs-keyword:contains(else)").after("else");
   $(`code:contains(${diagram_15})`).find(".hljs-keyword").remove();
+  $(`code:contains(${diagram_15})`).find(".hljs-string:contains(\'left_on/right_on\')").after("\'left_on/right_on\'");
+  $(`code:contains(${diagram_15})`).find(".hljs-string:contains(\'left_on/right_on\')").remove();
+  $(`code:contains(${diagram_15})`).find(".hljs-string:contains('on')").after("'on'");
+  $(`code:contains(${diagram_15})`).find(".hljs-string:contains('on')").remove();
 }
 
 function removePlotImages() {
diff --git a/pdf/README.md b/pdf/README.md
index 1a56493b0..3c6d59b6a 100644
--- a/pdf/README.md
+++ b/pdf/README.md
@@ -1,6 +1,5 @@
 How To Create PDF (on macOS)
 ============================
-**PDF file can also be purchased here: https://transactions.sendowl.com/products/78175486/4422834F/view**
 
 
 Setup
@@ -14,8 +13,8 @@ Printing to PDF
 ### Normal PDF
 * Open `index.html` in text editor and first remove element `<p><br></p>` before the `<h1>Libraries</h1>`.
 * Then replace the index and footer with contents of `pdf/index_for_pdf.html` file and save.
-* Disable internet connection and open the file in Chromium version 108.0.5328.0 (later versions will render the site incorrectly after index is added) with 'Cache killer' extension enabled.
-* Right click on the border of the site and select inspect. Select `<body>` element under 'Elements' tab and change top margin from 16 to 0 and top padding from 16 to 5 in 'Styles' tab.
+* Disable internet connection and open Chromium version 108.0.5328.0 (later versions will render the site incorrectly after index is added). Right click anywhere in the window and choose 'inspect'. Go to 'Network' tab and check 'Disable Cache'. Open the `index.html` file while keeping the inspect window open.
+* Right click on the border of the site and select inspect. Select `<body>` element under 'Elements' tab and change top margin and top padding from 16 to 0 in 'Styles' tab.
 * Change brightness of comments by right clicking on one of them and selecting inspect. Then click on the rectangle that represents color and toggle the color space to HSLA by clicking on the button with two vertical arrows. Change lightness (L) percentage to 77%.
 * Change the brightness of text to 13%.
 * Select 'Print...' with destination 'Save as PDF', paper size 'A4', 'Default' margins (top 10mm, right 9.5mm, bottom 8mm and left 10mm), 'Default' scale and no headers and footers and save (the document should be 51 pages long with last page empty).
@@ -26,8 +25,8 @@ Printing to PDF
 * Change all links in text to normal text and add a page number in brackets like that: '(p. <page_num>)' by running './pdf/remove_links.py' (Links can be found with this regex: `<strong>.*a href.*</strong>`).
 * Open `index.html` in text editor and first remove element `<p><br></p>` before the `<h1>Libraries</h1>`.
 * Then replace the index and footer with contents of `pdf/index_for_pdf_print.html` file and save.
-* Disable internet connection and open the file in Chromium version 108.0.5328.0 (later versions will render the site incorrectly after index is added) with 'Cache killer' extension enabled.
-* Right click on the border of the site and select inspect. Select `<body>` element under 'Elements' tab and change top margin from 16 to 0 and top padding from 16 to 5 in 'Styles' tab.
+* Disable internet connection and open Chromium version 108.0.5328.0 (later versions will render the site incorrectly after index is added). Right click anywhere in the window and choose 'inspect'. Go to 'Network' tab and check 'Disable Cache'. Open the `index.html` file while keeping the inspect window open.
+* Right click on the border of the site and select inspect. Select `<body>` element under 'Elements' tab and change top margin and top padding from 16 to 0 in 'Styles' tab.
 * Change brightness of elements by right clicking on them and selecting inspect. Then click on the rectangle that represents color and toggle the color space to HSLA by clicking on the button with two vertical arrows.
 * Change lightness (L) percentage to:
 * 0% for the text.
diff --git a/pdf/index_for_pdf.html b/pdf/index_for_pdf.html
index 54f6747f0..b151d3527 100644
--- a/pdf/index_for_pdf.html
+++ b/pdf/index_for_pdf.html
@@ -7,14 +7,14 @@ <h3 id="a">A</h3>
 <p><strong>abstract base classes, <a href="#abstractbaseclasses">4</a>, <a href="#abcsequence">19</a></strong><br>
 <strong>animation, <a href="#animation">40</a>, <a href="#pygame">42</a>-<a href="#basicmariobrothersexample">43</a></strong><br>
 <strong>argparse module, <a href="#argumentparser">22</a></strong><br>
-<strong>arguments, <a href="#arguments">10</a>, <a href="#partial">12</a>, <a href="#commandlinearguments">22</a></strong><br>
+<strong>arguments, <a href="#function">10</a>, <a href="#partial">12</a>, <a href="#commandlinearguments">22</a></strong><br>
 <strong>arrays, <a href="#array">29</a>, <a href="#numpy">37</a>-<a href="#indexing">38</a></strong><br>
 <strong>asyncio module, <a href="#coroutines">33</a></strong><br>
 <strong>audio, <a href="#audio">40</a>-<a href="#synthesizer">41</a>, <a href="#sound">42</a></strong>  </p>
 <h3 id="b">B</h3>
 <p><strong>beautifulsoup library, <a href="#scrapespythonsurlandlogofromitswikipediapage">35</a></strong><br>
-<strong>binary representation, <a href="#ints">7</a>, <a href="#binhex">8</a></strong><br>
-<strong>bitwise operators, <a href="#bitwiseoperators">8</a>, <a href="#operator">31</a></strong><br>
+<strong>binary representation, <a href="#ints">7</a>, <a href="#hexadecimalnumbers">8</a></strong><br>
+<strong>bitwise operators, <a href="#bitwiseoperators">8</a>, <a href="#operator">30</a></strong><br>
 <strong>bytes, <a href="#open">22</a>-<a href="#modes">23</a>, <a href="#pickle">25</a>, <a href="#bytes">28</a>-<a href="#memoryview">29</a></strong>  </p>
 <h3 id="c">C</h3>
 <p><strong>cache, <a href="#cache">13</a></strong><br>
@@ -25,29 +25,29 @@ <h3 id="c">C</h3>
 <strong>collections module, <a href="#dictionary">2</a>, <a href="#namedtuple">3</a>, <a href="#abstractbaseclasses">4</a>, <a href="#abcsequence">19</a>, <a href="#deque">29</a></strong><br>
 <strong>combinatorics, <a href="#combinatorics">8</a></strong><br>
 <strong>command line arguments, <a href="#commandlinearguments">22</a></strong><br>
-<strong>comprehensions, <a href="#comprehensions">11</a></strong><br>
-<strong>context manager, <a href="#contextmanager">17</a>, <a href="#readtextfromfile">23</a>, <a href="#or">27</a>, <a href="#or-1">30</a></strong><br>
+<strong>comprehensions, <a href="#list">1</a>, <a href="#dictionary">2</a>, <a href="#comprehensions">11</a></strong><br>
+<strong>context manager, <a href="#contextmanager">17</a>, <a href="#readtextfromfile">23</a>, <a href="#or">27</a>, <a href="#or-1">32</a></strong><br>
 <strong>copy function, <a href="#copy">15</a></strong><br>
 <strong>coroutine, <a href="#coroutines">33</a></strong><br>
 <strong>counter, <a href="#counter">2</a>, <a href="#generator">4</a>, <a href="#nonlocal">12</a>, <a href="#iterator-1">17</a></strong><br>
-<strong>csv, <a href="#csv">26</a>, <a href="#printsacsvspreadsheettotheconsole">34</a>, <a href="#dataframeencodedecode">46</a>, <a href="#displaysalinechartoftotalcoronavirusdeathspermilliongroupedbycontinent">47</a></strong><br>
+<strong>csv, <a href="#csv">26</a>, <a href="#printsacsvspreadsheettotheconsole">34</a>, <a href="#fileformats">46</a>, <a href="#displaysalinechartoftotalcovid19deathspermilliongroupedbycontinent">47</a></strong><br>
 <strong>curses module, <a href="#runsaterminalgamewhereyoucontrolanasteriskthatmustavoidnumbers">33</a>, <a href="#consoleapp">34</a></strong><br>
 <strong>cython, <a href="#typeannotations">15</a>, <a href="#cython">49</a></strong>  </p>
 <h3 id="d">D</h3>
-<p><strong>dataclasses module, <a href="#namedtupleenumdataclass">12</a>, <a href="#dataclass">15</a></strong><br>
+<p><strong>dataclasses module, <a href="#namedtupleenumdataclass">11</a>, <a href="#dataclass">15</a></strong><br>
 <strong>datetime module, <a href="#datetime">8</a>-<a href="#now">9</a></strong><br>
 <strong>decorator, <a href="#decorator">13</a>, <a href="#class">14</a>, <a href="#dataclass">15</a>, <a href="#sortable">16</a></strong><br>
 <strong>deques, <a href="#deque">29</a></strong><br>
-<strong>dictionaries, <a href="#dictionary">2</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">11</a>, <a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a>, <a href="#collectionsandtheirexceptions">21</a></strong><br>
+<strong>dictionaries, <a href="#dictionary">2</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">10</a>-<a href="#comprehensions">11</a>, <a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a>, <a href="#collectionsandtheirexceptions">21</a></strong><br>
 <strong>duck types, <a href="#ducktypes">16</a>-<a href="#abcsequence">19</a></strong>  </p>
 <h3 id="e">E</h3>
 <p><strong>enum module, <a href="#enum">19</a>-<a href="#inline-1">20</a></strong><br>
 <strong>enumerate function, <a href="#enumerate">3</a></strong><br>
-<strong>excel, <a href="#dataframeencodedecode">46</a></strong><br>
-<strong>exceptions, <a href="#exceptions">20</a>-<a href="#exceptionobject">21</a>, <a href="#exceptions-1">23</a>, <a href="#logging">32</a></strong><br>
+<strong>excel, <a href="#fileformats">46</a></strong><br>
+<strong>exceptions, <a href="#exceptions">20</a>-<a href="#exceptionobject">21</a>, <a href="#exceptions-1">23</a>, <a href="#logging">31</a></strong><br>
 <strong>exit function, <a href="#exit">21</a></strong>  </p>
 <h3 id="f">F</h3>
-<p><strong>files, <a href="#print">22</a>-<a href="#memoryview">29</a>, <a href="#runsabasicfileexplorerintheconsole">34</a>, <a href="#dataframeencodedecode">46</a></strong><br>
+<p><strong>files, <a href="#print">22</a>-<a href="#memoryview">29</a>, <a href="#runsabasicfileexplorerintheconsole">34</a>, <a href="#fileformats">46</a></strong><br>
 <strong>filter function, <a href="#mapfilterreduce">11</a></strong><br>
 <strong>flask library, <a href="#webapp">36</a></strong><br>
 <strong>floats, <a href="#abstractbaseclasses">4</a>, <a href="#floats">6</a>, <a href="#numbers">7</a></strong><br>
@@ -56,92 +56,92 @@ <h3 id="f">F</h3>
 <h3 id="g">G</h3>
 <p><strong>games, <a href="#runsaterminalgamewhereyoucontrolanasteriskthatmustavoidnumbers">33</a>, <a href="#pygame">42</a>-<a href="#basicmariobrothersexample">43</a></strong><br>
 <strong>generators, <a href="#generator">4</a>, <a href="#comprehensions">11</a>, <a href="#iterator-1">17</a></strong><br>
-<strong>global keyword, <a href="#nonlocal">12</a></strong><br>
-<strong>gui, <a href="#guiapp">35</a></strong>  </p>
+<strong>global keyword, <a href="#function">10</a>, <a href="#nonlocal">12</a></strong><br>
+<strong>gui app, <a href="#guiapp">35</a></strong>  </p>
 <h3 id="h">H</h3>
 <p><strong>hashable, <a href="#dataclass">15</a>, <a href="#hashable">16</a></strong><br>
-<strong>hexadecimal representation, <a href="#ints">7</a>, <a href="#binhex">8</a>, <a href="#encode-1">28</a></strong>  </p>
+<strong>hexadecimal representation, <a href="#ints">7</a>, <a href="#hexadecimalnumbers">8</a>, <a href="#encode-1">28</a></strong>  </p>
 <h3 id="i">I</h3>
 <p><strong>image, <a href="#scrapespythonsurlandlogofromitswikipediapage">35</a>, <a href="#image">39</a>-<a href="#animation">40</a>, <a href="#surface">42</a>-<a href="#basicmariobrothersexample">43</a></strong><br>
 <strong>imports, <a href="#imports">12</a></strong><br>
-<strong>inline, <a href="#otheruses">11</a>, <a href="#dataclass">15</a>, <a href="#inline-1">20</a></strong><br>
+<strong>inline, <a href="#inline">11</a>, <a href="#dataclass">15</a>, <a href="#inline-1">20</a></strong><br>
 <strong>input function, <a href="#input">22</a></strong><br>
-<strong>introspection,  <a href="#exceptionobject">21</a>, <a href="#introspection">32</a></strong><br>
-<strong>ints, <a href="#abstractbaseclasses">4</a>, <a href="#ints">7</a>, <a href="#random">8</a>, <a href="#encode-1">28</a></strong><br>
-<strong>is operator, <a href="#comparable">16</a>, <a href="#operator">31</a></strong><br>
+<strong>introspection,  <a href="#exceptionobject">21</a>, <a href="#introspection">31</a></strong><br>
+<strong>ints, <a href="#abstractbaseclasses">4</a>, <a href="#ints">7</a>-<a href="#random">8</a>, <a href="#encode-1">28</a></strong><br>
+<strong>is operator, <a href="#comparable">16</a>, <a href="#operator">30</a></strong><br>
 <strong>iterable, <a href="#abstractbaseclasses">4</a>, <a href="#iterable">18</a>, <a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a></strong><br>
 <strong>iterator, <a href="#enumerate">3</a>-<a href="#generator">4</a>, <a href="#comprehensions">11</a>, <a href="#iterator-1">17</a></strong><br>
 <strong>itertools module, <a href="#itertools">3</a>, <a href="#combinatorics">8</a></strong>  </p>
 <h3 id="j">J</h3>
-<p><strong>json, <a href="#json">25</a>, <a href="#restrequest">36</a>, <a href="#dataframeencodedecode">46</a></strong>  </p>
+<p><strong>json, <a href="#json">25</a>, <a href="#servingjson">36</a>, <a href="#fileformats">46</a></strong>  </p>
 <h3 id="l">L</h3>
 <p><strong>lambda, <a href="#lambda">11</a></strong><br>
-<strong>lists, <a href="#list">1</a>-<a href="#list">2</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">11</a>, <a href="#sequence">18</a>-<a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a>, <a href="#collectionsandtheirexceptions">21</a></strong><br>
+<strong>lists, <a href="#list">1</a>-<a href="#list">2</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">10</a>-<a href="#comprehensions">11</a>, <a href="#sequence">18</a>-<a href="#abcsequence">19</a>, <a href="#collectionsandtheirexceptions">21</a></strong><br>
 <strong>locale module, <a href="#sortable">16</a></strong><br>
-<strong>logging, <a href="#logging">32</a></strong>  </p>
+<strong>logging, <a href="#logging">31</a></strong>  </p>
 <h3 id="m">M</h3>
 <p><strong>main function, <a href="#main">1</a>, <a href="#basicscripttemplate">49</a></strong><br>
-<strong>match statement, <a href="#matchstatement">31</a></strong><br>
-<strong>matplotlib library, <a href="#plot">34</a>, <a href="#series">44</a>, <a href="#dataframeencodedecode">46</a></strong><br>
-<strong>map function, <a href="#mapfilterreduce">11</a>, <a href="#operator">31</a></strong><br>
+<strong>match statement, <a href="#matchstatement">30</a></strong><br>
+<strong>matplotlib library, <a href="#plot">34</a>, <a href="#pandas">44</a>, <a href="#dataframe">45</a></strong><br>
+<strong>map function, <a href="#mapfilterreduce">11</a>, <a href="#operator">30</a></strong><br>
 <strong>math module, <a href="#numbers">7</a></strong><br>
 <strong>memoryviews, <a href="#memoryview">29</a></strong><br>
 <strong>module, <a href="#imports">12</a></strong>  </p>
 <h3 id="n">N</h3>
-<p><strong>namedtuples, <a href="#namedtuple">3</a></strong><br>
+<p><strong>namedtuples, <a href="#namedtuple">3</a>, <a href="#example">6</a></strong><br>
 <strong>nonlocal keyword, <a href="#nonlocal">12</a></strong><br>
 <strong>numbers, <a href="#abstractbaseclasses">4</a>, <a href="#numbers-1">6</a>-<a href="#random">8</a></strong><br>
-<strong>numpy library, <a href="#numpy">37</a>-<a href="#indexing">38</a></strong>  </p>
+<strong>numpy library, <a href="#numpy">37</a>-<a href="#indexing">38</a>, <a href="#image">39</a>, <a href="#series">44</a></strong>  </p>
 <h3 id="o">O</h3>
-<p><strong>open function, <a href="#contextmanager">17</a>, <a href="#open">22</a>-<a href="#modes">23</a>, <a href="#readobjectfromjsonfile">25</a>, <a href="#readrowsfromcsvfile">26</a>, <a href="#readbytesfromfile">28</a></strong><br>
-<strong>operator module, <a href="#operator">31</a></strong><br>
+<p><strong>open function, <a href="#contextmanager">17</a>, <a href="#open">22</a>-<a href="#modes">23</a>, <a href="#readcollectionfromjsonfile">25</a>, <a href="#readrowsfromcsvfile">26</a>, <a href="#readbytesfromfile">28</a></strong><br>
+<strong>operator module, <a href="#operator">30</a></strong><br>
 <strong>os commands, <a href="#paths">23</a>-<a href="#shellcommands">25</a>, <a href="#runsabasicfileexplorerintheconsole">34</a></strong>  </p>
 <h3 id="p">P</h3>
-<p><strong>pandas library, <a href="#pandas">44</a>-<a href="#displaysamultiaxislinechartoftotalcoronaviruscasesandchangesinpricesofbitcoindowjonesandgold">48</a></strong><br>
+<p><strong>pandas library, <a href="#pandas">44</a>-<a href="#displaysamultiaxislinechartoftotalcovid19casesandchangesinpricesofbitcoindowjonesandgold">48</a></strong><br>
 <strong>partial function, <a href="#partial">12</a>, <a href="#userdefinedfunctionscannotbevaluessotheymustbewrapped">20</a></strong><br>
 <strong>paths, <a href="#paths">23</a>-<a href="#oscommands">24</a>, <a href="#runsabasicfileexplorerintheconsole">34</a></strong><br>
 <strong>pickle module, <a href="#pickle">25</a></strong><br>
 <strong>pillow library, <a href="#image">39</a>-<a href="#animation">40</a></strong><br>
-<strong>plotting, <a href="#plot">34</a>, <a href="#series">44</a>, <a href="#dataframeencodedecode">46</a>, <a href="#plotly">47</a>-<a href="#displaysamultiaxislinechartoftotalcoronaviruscasesandchangesinpricesofbitcoindowjonesandgold">48</a></strong><br>
+<strong>plotting, <a href="#plot">34</a>, <a href="#pandas">44</a>, <a href="#dataframe">45</a>, <a href="#plotly">47</a>-<a href="#displaysamultiaxislinechartoftotalcovid19casesandchangesinpricesofbitcoindowjonesandgold">48</a></strong><br>
 <strong>print function, <a href="#class">14</a>, <a href="#print">22</a></strong><br>
 <strong>profiling, <a href="#profiling">36</a>-<a href="#profilingbyline">37</a></strong><br>
 <strong>progress bar, <a href="#progressbar">34</a></strong><br>
-<strong>property decorator, <a href="#property">15</a></strong><br>
+<strong>property decorator, <a href="#property">15</a>, <a href="#hashable">16</a></strong><br>
 <strong>pygame library, <a href="#pygame">42</a>-<a href="#basicmariobrothersexample">43</a></strong>  </p>
 <h3 id="q">Q</h3>
-<p><strong>queues, <a href="#deque">29</a>, <a href="#queue">30</a>, <a href="#runsaterminalgamewhereyoucontrolanasteriskthatmustavoidnumbers">33</a></strong>  </p>
+<p><strong>queues, <a href="#deque">29</a>, <a href="#queue">32</a>, <a href="#runsaterminalgamewhereyoucontrolanasteriskthatmustavoidnumbers">33</a></strong>  </p>
 <h3 id="r">R</h3>
-<p><strong>random module, <a href="#random">8</a></strong><br>
+<p><strong>random module, <a href="#random">8</a>, <a href="#runsaterminalgamewhereyoucontrolanasteriskthatmustavoidnumbers">33</a>, <a href="#addsnoisetothewavfile">41</a></strong><br>
 <strong>ranges, <a href="#range">3</a>, <a href="#abstractbaseclasses">4</a></strong><br>
 <strong>recursion, <a href="#cache">13</a>, <a href="#builtinexceptions">21</a></strong><br>
-<strong>reduce function, <a href="#mapfilterreduce">11</a>, <a href="#operator">31</a></strong><br>
+<strong>reduce function, <a href="#mapfilterreduce">11</a></strong><br>
 <strong>regular expressions, <a href="#regex">5</a>-<a href="#specialsequences">6</a></strong><br>
 <strong>requests library, <a href="#scrapespythonsurlandlogofromitswikipediapage">35</a>, <a href="#startstheappinitsownthreadandqueriesitsrestapi">36</a></strong>  </p>
 <h3 id="s">S</h3>
 <p><strong>scope, <a href="#insidefunctiondefinition">10</a>, <a href="#nonlocal">12</a>, <a href="#complexexample">20</a></strong><br>
-<strong>scraping, <a href="#scraping">35</a>, <a href="#basicmariobrothersexample">43</a>, <a href="#dataframeencodedecode">46</a>, <a href="#displaysalinechartoftotalcoronavirusdeathspermilliongroupedbycontinent">47</a>-<a href="#displaysamultiaxislinechartoftotalcoronaviruscasesandchangesinpricesofbitcoindowjonesandgold">48</a></strong><br>
+<strong>scraping, <a href="#scraping">35</a>, <a href="#basicmariobrothersexample">43</a>, <a href="#fileformats">46</a>, <a href="#displaysalinechartoftotalcovid19deathspermilliongroupedbycontinent">47</a>-<a href="#displaysamultiaxislinechartoftotalcovid19casesandchangesinpricesofbitcoindowjonesandgold">48</a></strong><br>
 <strong>sequence, <a href="#abstractbaseclasses">4</a>, <a href="#sequence">18</a>-<a href="#abcsequence">19</a></strong><br>
-<strong>sets, <a href="#set">2</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">11</a>, <a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a>, <a href="#collectionsandtheirexceptions">21</a></strong><br>
+<strong>sets, <a href="#set">2</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">10</a>-<a href="#comprehensions">11</a>, <a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a>, <a href="#collectionsandtheirexceptions">21</a></strong><br>
 <strong>shell commands, <a href="#shellcommands">25</a></strong><br>
 <strong>sleep function, <a href="#progressbar">34</a></strong><br>
 <strong>sortable, <a href="#list">1</a>, <a href="#sortable">16</a></strong><br>
-<strong>splat operator, <a href="#splatoperator">10</a>-<a href="#otheruses">11</a>, <a href="#readrowsfromcsvfile">26</a></strong><br>
-<strong>sql, <a href="#sqlite">27</a>, <a href="#dataframeencodedecode">46</a></strong><br>
-<strong>statistics, <a href="#statistics">7</a>, <a href="#numpy">37</a>-<a href="#indexing">38</a>, <a href="#pandas">44</a>-<a href="#displaysamultiaxislinechartoftotalcoronaviruscasesandchangesinpricesofbitcoindowjonesandgold">48</a></strong><br>
+<strong>splat operator, <a href="#splatoperator">10</a>, <a href="#readrowsfromcsvfile">26</a></strong><br>
+<strong>sql, <a href="#sqlite">27</a>, <a href="#fileformats">46</a></strong><br>
+<strong>statistics, <a href="#statistics">7</a>, <a href="#numpy">37</a>-<a href="#indexing">38</a>, <a href="#pandas">44</a>-<a href="#displaysamultiaxislinechartoftotalcovid19casesandchangesinpricesofbitcoindowjonesandgold">48</a></strong><br>
 <strong>strings, <a href="#abstractbaseclasses">4</a>-<a href="#comparisonofpresentationtypes">7</a>, <a href="#class">14</a></strong><br>
 <strong>struct module, <a href="#struct">28</a>-<a href="#integertypesuseacapitalletterforunsignedtypeminimumandstandardsizesareinbrackets">29</a></strong><br>
 <strong>subprocess module, <a href="#sends11tothebasiccalculatorandcapturesitsoutput">25</a></strong><br>
-<strong>super function, <a href="#inheritance">14</a></strong><br>
+<strong>super function, <a href="#subclass">14</a></strong><br>
 <strong>sys module, <a href="#cache">13</a>, <a href="#exit">21</a>-<a href="#commandlinearguments">22</a></strong> </p>
 <h3 id="t">T</h3>
 <p><strong>table, <a href="#csv">26</a>, <a href="#example-1">27</a>, <a href="#table">34</a>, <a href="#numpy">37</a>-<a href="#indexing">38</a>, <a href="#dataframe">45</a>-<a href="#dataframeaggregatetransformmap">46</a></strong><br>
-<strong>template, <a href="#format">6</a>, <a href="#dynamicrequest">36</a></strong><br>
-<strong>threading module, <a href="#threading">30</a>, <a href="#startstheappinitsownthreadandqueriesitsrestapi">36</a></strong><br>
+<strong>template, <a href="#format">6</a>, <a href="#servinghtml">36</a></strong><br>
+<strong>threading module, <a href="#threading">32</a>, <a href="#startstheappinitsownthreadandqueriesitsrestapi">36</a></strong><br>
 <strong>time module, <a href="#progressbar">34</a>, <a href="#profiling">36</a></strong><br>
-<strong>tuples, <a href="#tuple">3</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">11</a>, <a href="#sequence">18</a>-<a href="#tableofrequiredandautomaticallyavailablespecialmethods">19</a></strong><br>
-<strong>type, <a href="#type">4</a></strong><br>
-<strong>type annotations, <a href="#typeannotations">15</a>, <a href="#introspection">32</a></strong>  </p>
+<strong>tuples, <a href="#tuple">3</a>, <a href="#abstractbaseclasses">4</a>, <a href="#otheruses">10</a>-<a href="#comprehensions">11</a>, <a href="#sequence">18</a>-<a href="#abcsequence">19</a></strong><br>
+<strong>type, <a href="#type">4</a>, <a href="#ducktypes">16</a>, <a href="#matchstatement">30</a></strong><br>
+<strong>type annotations, <a href="#typeannotations">15</a>, <a href="#introspection">31</a></strong>  </p>
 <h3 id="w">W</h3>
 <p><strong>wave module, <a href="#audio">40</a>-<a href="#writefloatsamplestowavfile">41</a></strong><br>
-<strong>web, <a href="#webapp">36</a></strong>  </p> 
+<strong>web app, <a href="#webapp">36</a></strong>  </p>
 </div>
\ No newline at end of file
diff --git a/pdf/index_for_pdf_print.html b/pdf/index_for_pdf_print.html
index e7bdcfeb7..5e9622832 100644
--- a/pdf/index_for_pdf_print.html
+++ b/pdf/index_for_pdf_print.html
@@ -14,7 +14,7 @@ <h3 id="a">A</h3>
 <h3 id="b">B</h3>
 <p><strong>beautifulsoup library, 35</strong><br>
 <strong>binary representation, 7, 8</strong><br>
-<strong>bitwise operators, 8, 31</strong><br>
+<strong>bitwise operators, 8, 30</strong><br>
 <strong>bytes, 22-23, 25, 28-29</strong>  </p>
 <h3 id="c">C</h3>
 <p><strong>cache, 13</strong><br>
@@ -25,8 +25,8 @@ <h3 id="c">C</h3>
 <strong>collections module, 2, 3, 4, 19, 29</strong><br>
 <strong>combinatorics, 8</strong><br>
 <strong>command line arguments, 22</strong><br>
-<strong>comprehensions, 11</strong><br>
-<strong>context manager, 17, 23, 27, 30</strong><br>
+<strong>comprehensions, 1, 2, 11</strong><br>
+<strong>context manager, 17, 23, 27, 32</strong><br>
 <strong>copy function, 15</strong><br>
 <strong>coroutine, 33</strong><br>
 <strong>counter, 2, 4, 12, 17</strong><br>
@@ -34,17 +34,17 @@ <h3 id="c">C</h3>
 <strong>curses module, 33, 34</strong><br>
 <strong>cython, 15, 49</strong>  </p>
 <h3 id="d">D</h3>
-<p><strong>dataclasses module, 12, 15</strong><br>
+<p><strong>dataclasses module, 11, 15</strong><br>
 <strong>datetime module, 8-9</strong><br>
 <strong>decorator, 13, 14, 15, 16</strong><br>
 <strong>deques, 29</strong><br>
-<strong>dictionaries, 2, 4, 11, 19, 21</strong><br>
+<strong>dictionaries, 2, 4, 10-11, 19, 21</strong><br>
 <strong>duck types, 16-19</strong>  </p>
 <h3 id="e">E</h3>
 <p><strong>enum module, 19-20</strong><br>
 <strong>enumerate function, 3</strong><br>
 <strong>excel, 46</strong><br>
-<strong>exceptions, 20-21, 23, 32</strong><br>
+<strong>exceptions, 20-21, 23, 31</strong><br>
 <strong>exit function, 21</strong>  </p>
 <h3 id="f">F</h3>
 <p><strong>files, 22-29, 34, 46</strong><br>
@@ -56,7 +56,7 @@ <h3 id="f">F</h3>
 <h3 id="g">G</h3>
 <p><strong>games, 33, 42-43</strong><br>
 <strong>generators, 4, 11, 17</strong><br>
-<strong>global keyword, 12</strong><br>
+<strong>global keyword, 10, 12</strong><br>
 <strong>gui, 35</strong>  </p>
 <h3 id="h">H</h3>
 <p><strong>hashable, 15, 16</strong><br>
@@ -66,9 +66,9 @@ <h3 id="i">I</h3>
 <strong>imports, 12</strong><br>
 <strong>inline, 11, 15, 20</strong><br>
 <strong>input function, 22</strong><br>
-<strong>introspection, 21, 32</strong><br>
-<strong>ints, 4, 7, 8, 28</strong><br>
-<strong>is operator, 16, 31</strong><br>
+<strong>introspection, 21, 31</strong><br>
+<strong>ints, 4, 7-8, 28</strong><br>
+<strong>is operator, 16, 30</strong><br>
 <strong>iterable, 4, 18, 19</strong><br>
 <strong>iterator, 3-4, 11, 17</strong><br>
 <strong>itertools module, 3, 8</strong>  </p>
@@ -76,25 +76,25 @@ <h3 id="j">J</h3>
 <p><strong>json, 25, 36, 46</strong>  </p>
 <h3 id="l">L</h3>
 <p><strong>lambda, 11</strong><br>
-<strong>lists, 1-2, 4, 11, 18-19, 21</strong><br>
+<strong>lists, 1-2, 4, 10-11, 18-19, 21</strong><br>
 <strong>locale module, 16</strong><br>
-<strong>logging, 32</strong>  </p>
+<strong>logging, 31</strong>  </p>
 <h3 id="m">M</h3>
 <p><strong>main function, 1, 49</strong><br>
-<strong>match statement, 31</strong><br>
-<strong>matplotlib library, 34, 44, 46</strong><br>
-<strong>map function, 11, 31</strong><br>
+<strong>match statement, 30</strong><br>
+<strong>matplotlib library, 34, 44, 45</strong><br>
+<strong>map function, 11, 30</strong><br>
 <strong>math module, 7</strong><br>
 <strong>memoryviews, 29</strong><br>
 <strong>module, 12</strong>  </p>
 <h3 id="n">N</h3>
-<p><strong>namedtuples, 3</strong><br>
+<p><strong>namedtuples, 3, 6</strong><br>
 <strong>nonlocal keyword, 12</strong><br>
 <strong>numbers, 4, 6-8</strong><br>
-<strong>numpy library, 37-38</strong>  </p>
+<strong>numpy library, 37-38, 39, 44</strong>  </p>
 <h3 id="o">O</h3>
 <p><strong>open function, 17, 22-23, 25, 26, 28</strong><br>
-<strong>operator module, 31</strong><br>
+<strong>operator module, 30</strong><br>
 <strong>os commands, 23-25, 34</strong>  </p>
 <h3 id="p">P</h3>
 <p><strong>pandas library, 44-48</strong><br>
@@ -102,30 +102,30 @@ <h3 id="p">P</h3>
 <strong>paths, 23-24, 34</strong><br>
 <strong>pickle module, 25</strong><br>
 <strong>pillow library, 39-40</strong><br>
-<strong>plotting, 34, 44, 46, 47-48</strong><br>
+<strong>plotting, 34, 44, 45, 47-48</strong><br>
 <strong>print function, 14, 22</strong><br>
 <strong>profiling, 36-37</strong><br>
 <strong>progress bar, 34</strong><br>
-<strong>property decorator, 15</strong><br>
+<strong>property decorator, 15, 16</strong><br>
 <strong>pygame library, 42-43</strong>  </p>
 <h3 id="q">Q</h3>
-<p><strong>queues, 29, 30, 33</strong>  </p>
+<p><strong>queues, 29, 32, 33</strong>  </p>
 <h3 id="r">R</h3>
-<p><strong>random module, 8</strong><br>
+<p><strong>random module, 8, 33, 41</strong><br>
 <strong>ranges, 3, 4</strong><br>
 <strong>recursion, 13, 21</strong><br>
-<strong>reduce function, 11, 31</strong><br>
+<strong>reduce function, 11</strong><br>
 <strong>regular expressions, 5-6</strong><br>
 <strong>requests library, 35, 36</strong>  </p>
 <h3 id="s">S</h3>
 <p><strong>scope, 10, 12, 20</strong><br>
 <strong>scraping, 35, 43, 46, 47-48</strong><br>
 <strong>sequence, 4, 18-19</strong><br>
-<strong>sets, 2, 4, 11, 19, 21</strong><br>
+<strong>sets, 2, 4, 10-11, 19, 21</strong><br>
 <strong>shell commands, 25</strong><br>
 <strong>sleep function, 34</strong><br>
 <strong>sortable, 1, 16</strong><br>
-<strong>splat operator, 10-11, 26</strong><br>
+<strong>splat operator, 10, 26</strong><br>
 <strong>sql, 27, 46</strong><br>
 <strong>statistics, 7, 37-38, 44-48</strong><br>
 <strong>strings, 4-7, 14</strong><br>
@@ -136,11 +136,11 @@ <h3 id="s">S</h3>
 <h3 id="t">T</h3>
 <p><strong>table, 26, 27, 34, 37-38, 45-46</strong><br>
 <strong>template, 6, 36</strong><br>
-<strong>threading module, 30, 36</strong><br>
+<strong>threading module, 32, 36</strong><br>
 <strong>time module, 34, 36</strong><br>
-<strong>tuples, 3, 4, 11, 18-19</strong><br>
-<strong>type, 4</strong><br>
-<strong>type annotations, 15, 32</strong>  </p>
+<strong>tuples, 3, 4, 10-11, 18-19</strong><br>
+<strong>type, 4, 16, 30</strong><br>
+<strong>type annotations, 15, 31</strong>  </p>
 <h3 id="w">W</h3>
 <p><strong>wave module, 40-41</strong><br>
 <strong>web, 36</strong>  </p> 
diff --git a/pdf/remove_links.py b/pdf/remove_links.py
index 527d8d533..5b8941bc6 100755
--- a/pdf/remove_links.py
+++ b/pdf/remove_links.py
@@ -7,27 +7,28 @@
 
 
 MATCHES = {
-    '<strong>For details about sorted(), min() and max() see <a href="#sortable">sortable</a>.</strong>': '<strong>For details about sorted(), min() and max() see sortable (p. 16).</strong>',
-    '<strong>Module <a href="#operator">operator</a> provides functions itemgetter() and mul() that offer the same functionality as <a href="#lambda">lambda</a> expressions above.</strong>': '<strong>Module \'operator\' (p. 31) provides functions itemgetter() and mul() that offer the same functionality as lambda expressions (p. 11) above.</strong>',
+    '<strong>For details about sort(), sorted(), min() and max() see <a href="#sortable">Sortable</a>.</strong>': '<strong>For details about sort(), sorted(), min() and max() see Sortable (p. 16).</strong>',
+    '<strong>Module <a href="#operator">operator</a> has function itemgetter() that can replace listed <a href="#lambda">lambdas</a>.</strong>': '<strong>Module \'operator\' has function itemgetter() that can replace listed lambdas (p. 31).</strong>',
+    '<strong>This text uses the term collection instead of iterable. For rationale see <a href="#collection">Collection</a>.</strong>': '<strong>This text uses the term collection instead of iterable. For rationale see Collection (p. 18).</strong>',
     '<strong>Adding <code class="python hljs"><span class="hljs-string">\'!r\'</span></code> to the expression converts object to string by calling its <a href="#class">repr()</a> method.</strong>': '<strong>Adding <code class="python hljs"><span class="hljs-string">\'!r\'</span></code> to the expression converts object to string by calling its repr() method.</strong>',
-    '<strong>It can be any <a href="#callable">callable</a>, but is usually implemented as a function that returns a <a href="#closure">closure</a>.</strong>': '<strong>It can be any callable, but is usually implemented as a function that returns a closure.</strong>',
+    '<strong>A decorator takes a function, adds some functionality and returns it. It can be any <a href="#callable">callable</a>, but is usually implemented as a function that returns a <a href="#closure">closure</a>.</strong>': '<strong>A decorator takes a function, adds some functionality and returns it. It can be any callable (p.&nbsp;17), but is usually implemented as a function that returns a closure.</strong>',
     '<strong>Hints are used by type checkers like <a href="https://pypi.org/project/mypy/">mypy</a>, data validation libraries such as <a href="https://pypi.org/project/pydantic/">Pydantic</a> and lately also by <a href="https://pypi.org/project/Cython/">Cython</a> compiler. However, they are not enforced by CPython interpreter.</strong>': '<strong>Hints are used by type checkers like mypy, data validation libraries such as Pydantic and lately also by Cython compiler. However, they are not enforced by CPython interpreter.</strong>',
     '<strong>Objects can be made <a href="#sortable">sortable</a> with <code class="python hljs"><span class="hljs-string">\'order=True\'</span></code> and immutable with <code class="python hljs"><span class="hljs-string">\'frozen=True\'</span></code>.</strong>': '<strong>Objects can be made sortable with <code class="python hljs"><span class="hljs-string">\'order=True\'</span></code> and immutable with <code class="python hljs"><span class="hljs-string">\'frozen=True\'</span></code>.</strong>',
     '<strong>For object to be <a href="#hashable">hashable</a>, all attributes must be hashable and \'frozen\' must be True.</strong>': '<strong>For object to be hashable, all attributes must be hashable and \'frozen\' must be True.</strong>',
-    '<strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">\'&lt;attr_name&gt;: list = []\'</span></code> would make a list that is shared among all instances. Its \'default_factory\' argument can be any <a href="#callable">callable</a>.</strong>': '<strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">\'&lt;attr_name&gt;: list = []\'</span></code> would make a list that is shared among all instances. Its \'default_factory\' argument can be any callable (p. 17).</strong>',
-    '<strong>Sequence iterators returned by the <a href="#iterator">iter()</a> function, such as list_iterator and set_iterator.</strong>': '<strong>Sequence iterators returned by the iter() function, such as list_iterator and set_iterator.</strong>',
+    '<strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">\'&lt;attr_name&gt;: list = []\'</span></code> would make a list that is shared among all instances. Its \'default_factory\' argument accepts any <a href="#callable">callable</a> object.</strong>': '<strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">\'&lt;attr_name&gt;: list = []\'</span></code> would make a list that is shared among all instances. Its \'default_factory\' argument accepts any callable object.</strong>',
+    '<strong>Sequence iterators returned by the <a href="#iterator">iter()</a> function, such as list_iterator, etc.</strong>': '<strong>Sequence iterators returned by the iter() function, such as list_iterator and set_iterator.</strong>',
     '<strong>Objects returned by the <a href="#itertools">itertools</a> module, such as count, repeat and cycle.</strong>': '<strong>Objects returned by the itertools module, such as count, repeat and cycle (p. 3).</strong>',
     '<strong>Generators returned by the <a href="#generator">generator functions</a> and <a href="#comprehensions">generator expressions</a>.</strong>': '<strong>Generators returned by the generator functions (p. 4) and generator expressions (p. 11).</strong>',
     '<strong>File objects returned by the <a href="#open">open()</a> function, etc.</strong>': '<strong>File objects returned by the open() function (p. 22), etc.</strong>',
-    '<strong>Use <code class="python hljs"><span class="hljs-string">\'logging.exception(&lt;str&gt;)\'</span></code> to log the passed message, followed by the full error message of the caught exception. For details see <a href="#logging">logging</a>.</strong>': '<strong>Use <code class="python hljs"><span class="hljs-string">\'logging.exception(&lt;str&gt;)\'</span></code> to log the passed message, followed by the full error message of the caught exception. For details see logging (p. 32).</strong>',
-    '<strong>Functions report OS related errors by raising either OSError or one of its <a href="#exceptions-1">subclasses</a>.</strong>': '<strong>Functions report OS related errors by raising OSError or one of its subclasses (p. 23).</strong>',
-    '<strong>To print the spreadsheet to the console use <a href="#table">Tabulate</a> library.</strong>': '<strong>To print the spreadsheet to the console use Tabulate library (p. 34).</strong>',
-    '<strong>For XML and binary Excel files (xlsx, xlsm and xlsb) use <a href="#dataframeplotencodedecode">Pandas</a> library.</strong>': '<strong>For XML and binary Excel files (xlsx, xlsm and xlsb) use Pandas library (p. 46).</strong>',
+    '<strong>Use <code class="python hljs"><span class="hljs-string">\'logging.exception(&lt;str&gt;)\'</span></code> to log the passed message, followed by the full error message of the caught exception. For details about setting up the logger see <a href="#logging">Logging</a>.</strong>': '<strong>Use <code class="python hljs"><span class="hljs-string">\'logging.exception(&lt;str&gt;)\'</span></code> to log the passed message, followed by the full error message of the caught exception. For details about the logger setup see Logging (p. 31).</strong>',
+    '<strong>Functions report OS related errors by raising OSError or one of its <a href="#exceptions-1">subclasses</a>.</strong>': '<strong>Functions report OS related errors by raising OSError or one of its subclasses (p. 23).</strong>',
+    '<strong>Without the <code class="python hljs"><span class="hljs-string">\'newline=""\'</span></code> argument, every \'\\r\\n\' sequence that is embedded inside a quoted field will get converted to \'\\n\'! For details about newline argument see <a href="#open">Open</a>.</strong>': '<strong>Without the <code class="python hljs"><span class="hljs-string">\'newline=""\'</span></code> argument, every \'\\r\\n\' sequence that is embedded inside a quoted field will get converted to \'\\n\'! For details about newline arg. see Open (p. 22).</strong>',
+    '<strong>To print the spreadsheet to the console use <a href="#table">Tabulate</a> or PrettyTable library.</strong>': '<strong>To print the spreadsheet to the console use Tabulate or PrettyTable library (p. 34).</strong>',
+    '<strong>For XML and binary Excel files (xlsx, xlsm and xlsb) use <a href="#fileformats">Pandas</a> library.</strong>': '<strong>For XML and binary Excel files (xlsx, xlsm and xlsb) use Pandas library (p. 46).</strong>',
     '<strong>Bools will be stored and returned as ints and dates as <a href="#encode">ISO formatted strings</a>.</strong>': '<strong>Bools will be stored and returned as ints and dates as ISO formatted strings (p. 9).</strong>',
     '<strong>ProcessPoolExecutor provides true parallelism but: everything sent to/from workers must be <a href="#pickle">pickable</a>, queues must be sent using executor\'s \'initargs\' and \'initializer\' parameters, and executor should only be reachable via <code class="python hljs"><span class="hljs-string">\'if __name__ == "__main__": ...\'</span></code>.</strong>': '<strong>ProcessPoolExecutor provides true parallelism but: everything sent to/from workers must be pickable, queues must be sent using executor\'s \'initargs\' and \'initializer\' parameters, and executor should only be reachable via <code class="python hljs"><span class="hljs-string">\'if __name__ == "__main__": ...\'</span></code>.</strong>',
-    '<strong>Asyncio module also provides its own <a href="#queue">Queue</a>, <a href="#semaphoreeventbarrier">Event</a>, <a href="#lock">Lock</a> and <a href="#semaphoreeventbarrier">Semaphore</a> classes.</strong>': '<strong>Asyncio module also provides its own Queue, Event, Lock and Semaphore classes (p. 30).</strong>',
     '<strong>Install a WSGI server like <a href="https://flask.palletsprojects.com/en/latest/deploying/waitress/">Waitress</a> and a HTTP server such as <a href="https://flask.palletsprojects.com/en/latest/deploying/nginx/">Nginx</a> for better security.</strong>': '<strong>Install a WSGI server like Waitress and a HTTP server such as Nginx for better security.</strong>',
-    '<strong>Data analysis library. For examples see <a href="#displays-a-line-chart-of-total-coronavirus-deaths-per-million-grouped-by-continent">Plotly</a>.</strong>': '<strong>Data analysis library. For examples see Plotly (p. 47).</strong>',
+    '<strong>Data analysis library. For examples see <a href="#plotly">Plotly</a>.</strong>': '<strong>Data analysis library. For examples see Plotly (p. 47).</strong>',
 }
 
 
diff --git a/web/OnlineWebFonts_COM_cb7eb796ae7de7195a34c485cacebad1/@font-face/9f94dc20bb2a09c15241d3a880b7ad01-ss2.woff b/web/OnlineWebFonts_COM_cb7eb796ae7de7195a34c485cacebad1/@font-face/9f94dc20bb2a09c15241d3a880b7ad01-ss2.woff
new file mode 100644
index 000000000..a60995641
Binary files /dev/null and b/web/OnlineWebFonts_COM_cb7eb796ae7de7195a34c485cacebad1/@font-face/9f94dc20bb2a09c15241d3a880b7ad01-ss2.woff differ
diff --git a/web/script_2.js b/web/script_2.js
index 7484625a2..d0a46acb3 100644
--- a/web/script_2.js
+++ b/web/script_2.js
@@ -2,11 +2,11 @@ const TOC =
   '<strong>ToC</strong> = {\n' +
   '    <strong><span class="hljs-string">\'1. Collections\'</span></strong>: [<a href="#list">List</a>, <a href="#dictionary">Dictionary</a>, <a href="#set">Set</a>, <a href="#tuple">Tuple</a>, <a href="#range">Range</a>, <a href="#enumerate">Enumerate</a>, <a href="#iterator">Iterator</a>, <a href="#generator">Generator</a>],\n' +
   '    <strong><span class="hljs-string">\'2. Types\'</span></strong>:       [<a href="#type">Type</a>, <a href="#string">String</a>, <a href="#regex">Regular_Exp</a>, <a href="#format">Format</a>, <a href="#numbers">Numbers</a>, <a href="#combinatorics">Combinatorics</a>, <a href="#datetime">Datetime</a>],\n' +
-  '    <strong><span class="hljs-string">\'3. Syntax\'</span></strong>:      [<a href="#arguments">Args</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#ducktypes">Duck_Types</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Exception</a>],\n' +
+  '    <strong><span class="hljs-string">\'3. Syntax\'</span></strong>:      [<a href="#function">Function</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#ducktypes">Duck_Type</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Except</a>],\n' +
   '    <strong><span class="hljs-string">\'4. System\'</span></strong>:      [<a href="#exit">Exit</a>, <a href="#print">Print</a>, <a href="#input">Input</a>, <a href="#commandlinearguments">Command_Line_Arguments</a>, <a href="#open">Open</a>, <a href="#paths">Path</a>, <a href="#oscommands">OS_Commands</a>],\n' +
   '    <strong><span class="hljs-string">\'5. Data\'</span></strong>:        [<a href="#json">JSON</a>, <a href="#pickle">Pickle</a>, <a href="#csv">CSV</a>, <a href="#sqlite">SQLite</a>, <a href="#bytes">Bytes</a>, <a href="#struct">Struct</a>, <a href="#array">Array</a>, <a href="#memoryview">Memory_View</a>, <a href="#deque">Deque</a>],\n' +
-  '    <strong><span class="hljs-string">\'6. Advanced\'</span></strong>:    [<a href="#threading">Threading</a>, <a href="#operator">Operator</a>, <a href="#matchstatement">Match_Stmt</a>, <a href="#logging">Logging</a>, <a href="#introspection">Introspection</a>, <a href="#coroutines">Coroutines</a>],\n' +
-  '    <strong><span class="hljs-string">\'7. Libraries\'</span></strong>:   [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#consoleapp">Console_App</a>, <a href="#guiapp">GUI</a>, <a href="#scraping">Scraping</a>, <a href="#web">Web</a>, <a href="#profiling">Profile</a>],\n' +
+  '    <strong><span class="hljs-string">\'6. Advanced\'</span></strong>:    [<a href="#operator">Operator</a>, <a href="#matchstatement">Match_Stmt</a>, <a href="#logging">Logging</a>, <a href="#introspection">Introspection</a>, <a href="#threading">Threading</a>, <a href="#coroutines">Coroutines</a>],\n' +
+  '    <strong><span class="hljs-string">\'7. Libraries\'</span></strong>:   [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#consoleapp">Console_App</a>, <a href="#guiapp">GUI</a>, <a href="#scraping">Scraping</a>, <a href="#webapp">Web</a>, <a href="#profiling">Profile</a>],\n' +
   '    <strong><span class="hljs-string">\'8. Multimedia\'</span></strong>:  [<a href="#numpy">NumPy</a>, <a href="#image">Image</a>, <a href="#animation">Animation</a>, <a href="#audio">Audio</a>, <a href="#synthesizer">Synthesizer</a>, <a href="#pygame">Pygame</a>, <a href="#pandas">Pandas</a>, <a href="#plotly">Plotly</a>]\n' +
   '}\n';
 
@@ -18,7 +18,7 @@ const TOC_MOBILE =
   '    <strong><span class="hljs-string">\'2. Types\'</span></strong>:       [<a href="#type">Type</a>, <a href="#string">String</a>, <a href="#regex">Regular_Exp</a>,\n' +
   '                       <a href="#format">Format</a>, <a href="#numbers">Numbers</a>,\n' +
   '                       <a href="#combinatorics">Combinatorics</a>, <a href="#datetime">Datetime</a>],\n' +
-  '    <strong><span class="hljs-string">\'3. Syntax\'</span></strong>:      [<a href="#arguments">Arguments</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>,\n' +
+  '    <strong><span class="hljs-string">\'3. Syntax\'</span></strong>:      [<a href="#function">Function</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>,\n' +
   '                       <a href="#decorator">Decorator</a>, <a href="#class">Class</a>,\n' +
   '                       <a href="#ducktypes">Duck_Types</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Except</a>],\n' +
   '    <strong><span class="hljs-string">\'4. System\'</span></strong>:      [<a href="#exit">Exit</a>, <a href="#print">Print</a>, <a href="#input">Input</a>,\n' +
@@ -27,12 +27,12 @@ const TOC_MOBILE =
   '    <strong><span class="hljs-string">\'5. Data\'</span></strong>:        [<a href="#json">JSON</a>, <a href="#pickle">Pickle</a>, <a href="#csv">CSV</a>, <a href="#sqlite">SQLite</a>,\n' +
   '                       <a href="#bytes">Bytes</a>, <a href="#struct">Struct</a>, <a href="#array">Array</a>,\n' +
   '                       <a href="#memoryview">Memory_View</a>, <a href="#deque">Deque</a>],\n' +
-  '    <strong><span class="hljs-string">\'6. Advanced\'</span></strong>:    [<a href="#threading">Threading</a>, <a href="#operator">Operator</a>,\n' +
-  '                       <a href="#matchstatement">Match_Stmt</a>, <a href="#logging">Logging</a>, \n' +
-  '                       <a href="#introspection">Introspection</a>, <a href="#coroutines">Coroutines</a>],\n' +
+  '    <strong><span class="hljs-string">\'6. Advanced\'</span></strong>:    [<a href="#operator">Operator</a>, <a href="#matchstatement">Match_Statement</a>,\n' +
+  '                       <a href="#logging">Logging</a>, <a href="#introspection">Introspection</a>,\n' +
+  '                       <a href="#threading">Threading</a>, <a href="#coroutines">Coroutines</a>],\n' +
   '    <strong><span class="hljs-string">\'7. Libraries\'</span></strong>:   [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>,\n' +
   '                       <a href="#consoleapp">Console_App</a>, <a href="#guiapp">GUI_App</a>,\n' +
-  '                       <a href="#scraping">Scraping</a>, <a href="#web">Web</a>, <a href="#profiling">Profiling</a>],\n' +
+  '                       <a href="#scraping">Scraping</a>, <a href="#webapp">Web</a>, <a href="#profiling">Profiling</a>],\n' +
   '    <strong><span class="hljs-string">\'8. Multimedia\'</span></strong>:  [<a href="#numpy">NumPy</a>, <a href="#image">Image</a>, <a href="#animation">Animation</a>,\n' +
   '                       <a href="#audio">Audio</a>, <a href="#synthesizer">Synthesizer</a>,\n' +
   '                       <a href="#pygame">Pygame</a>, <a href="#pandas">Pandas</a>, <a href="#plotly">Plotly</a>]\n' +
diff --git a/web/style.css b/web/style.css
index 87e0fb4a6..1d3f07860 100644
--- a/web/style.css
+++ b/web/style.css
@@ -129,7 +129,7 @@ a:not(:hover) {
 pre,
 code,
 textarea {
-  font-family: "Menlo", "Menlo Web", monospace;
+  font-family: "Menlo", "Menlo Web", "Menlo Web ss", monospace;
 }
 
 code {
@@ -277,6 +277,12 @@ ul {
   font-weight: bold;
 }
 
+@font-face {font-family: "Menlo web ss";
+  src: url("OnlineWebFonts_COM_cb7eb796ae7de7195a34c485cacebad1\\@font-face\\9f94dc20bb2a09c15241d3a880b7ad01-ss2.woff") format("woff");
+  font-weight: normal;
+}
+
+
 .join,
 .link,
 .node rect {
diff --git a/web/style_dark3.css b/web/style_dark3.css
index 2f74cc560..3b39fdbf7 100644
--- a/web/style_dark3.css
+++ b/web/style_dark3.css
@@ -129,7 +129,7 @@ a:not(:hover) {
 pre,
 code,
 textarea {
-  font-family: "Menlo", "Menlo Web", monospace;
+  font-family: "Menlo", "Menlo Web", "Menlo Web ss", monospace;
 }
 
 code {
@@ -281,6 +281,12 @@ ul {
   font-weight: bold;
 }
 
+@font-face {font-family: "Menlo web ss";
+  src: url("OnlineWebFonts_COM_cb7eb796ae7de7195a34c485cacebad1\\@font-face\\9f94dc20bb2a09c15241d3a880b7ad01-ss2.woff") format("woff");
+  font-weight: normal;
+}
+
+
 .join,
 .link,
 .node rect {
diff --git a/web/template.html b/web/template.html
index ed249d980..9b8b5fd4c 100644
--- a/web/template.html
+++ b/web/template.html
@@ -13,8 +13,9 @@
   <link rel="stylesheet" href="web/style.css">
 
   <script>
-    // Checks if URL ends with "index.html?dark=true"
-    if (window.location.search.search(/[?&]theme=dark3/) !== -1) {
+    // Uses dark theme 3 if it's specified in query string orbrowser prefers dark mode and 
+    // theme is not explicitly set.
+    if ((window.location.search.search(/[?&]theme=dark3/) !== -1) || ((window.location.search.search(/[?&]theme=/) == -1) && (window.matchMedia('(prefers-color-scheme: dark)').matches))) {
       document.write("<link rel=\"stylesheet\" href=\"web/default_dark3.min.css\">");
       document.write("<link rel=\"stylesheet\" href=\"web/style_dark3.css\">");
     }
