From 159c457d889a4ab2854848ceae51e572230509ba Mon Sep 17 00:00:00 2001 From: Keefr Date: Tue, 12 Jul 2022 19:52:01 -0400 Subject: [PATCH] added a copy of index --- index copy.html | 2918 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 2918 insertions(+) create mode 100644 index copy.html diff --git a/index copy.html b/index copy.html new file mode 100644 index 000000000..960485f28 --- /dev/null +++ b/index copy.html @@ -0,0 +1,2918 @@ + + + + + + + Comprehensive Python Cheatsheet + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+ + +
+ +

Comprehensive Python Cheatsheet


#Contents

ToC = {
+    '1. Collections': [List, Dictionary, Set, Tuple, Range, Enumerate, Iterator, Generator],
+    '2. Types':       [Type, String, Regular_Exp, Format, Numbers, Combinatorics, Datetime],
+    '3. Syntax':      [Args, Inline, Import, Decorator, Class, Duck_Types, Enum, Exception],
+    '4. System':      [Exit, Print, Input, Command_Line_Arguments, Open, Path, OS_Commands],
+    '5. Data':        [JSON, Pickle, CSV, SQLite, Bytes, Struct, Array, Memory_View, Deque],
+    '6. Advanced':    [Threading, Operator, Introspection, Metaprograming, Eval, Coroutine],
+    '7. Libraries':   [Progress_Bar, Plot, Table, Curses, Logging, Scraping, Web, Profile,
+                       NumPy, Image, Audio, Games, Data]
+}
+
+ + + + + + +

#Main

if __name__ == '__main__':     # Runs main() if file wasn't imported.
+    main()
+
+ +

#List

<list> = <list>[<slice>]       # Or: <list>[from_inclusive : to_exclusive : ±step]
+
+ +
<list>.append(<el>)            # Or: <list> += [<el>]
+<list>.extend(<collection>)    # Or: <list> += <collection>
+
+
<list>.sort()                  # Sorts in ascending order.
+<list>.reverse()               # Reverses the list in-place.
+<list> = sorted(<collection>)  # Returns a new sorted list.
+<iter> = reversed(<list>)      # Returns reversed iterator.
+
+
sum_of_elements  = sum(<collection>)
+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>)
+
+ +
<list>.insert(<int>, <el>)     # Inserts item at index and moves the rest to the right.
+<el>  = <list>.pop([<int>])    # Removes and returns item at index or from the end.
+<int> = <list>.count(<el>)     # Returns number of occurrences. Also works on strings.
+<int> = <list>.index(<el>)     # Returns index of the first occurrence or raises ValueError.
+<list>.remove(<el>)            # Removes first occurrence of the item or raises ValueError.
+<list>.clear()                 # Removes all items. Also works on dictionary and set.
+
+

#Dictionary

<view> = <dict>.keys()                          # Coll. of keys that reflects changes.
+<view> = <dict>.values()                        # Coll. of values that reflects changes.
+<view> = <dict>.items()                         # Coll. of key-value tuples that reflects chgs.
+
+ +
value  = <dict>.get(key, default=None)          # Returns default if key is missing.
+value  = <dict>.setdefault(key, default=None)   # Returns and writes default if key is missing.
+<dict> = collections.defaultdict(<type>)        # Creates a dict with default value of type.
+<dict> = collections.defaultdict(lambda: 1)     # Creates a dict with default value 1.
+
+
<dict> = dict(<collection>)                     # Creates a dict from coll. of key-value pairs.
+<dict> = dict(zip(keys, values))                # Creates a dict from two collections.
+<dict> = dict.fromkeys(keys [, value])          # Creates a dict from collection of keys.
+
+
<dict>.update(<dict>)                           # Adds items. Replaces ones with matching keys.
+value = <dict>.pop(key)                         # Removes item or raises KeyError.
+{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}  # Returns a dictionary, filtered by keys.
+
+

Counter

>>> from collections import Counter
+>>> colors = ['blue', 'blue', 'blue', 'red', 'red']
+>>> counter = Counter(colors)
+>>> counter['yellow'] += 1
+Counter({'blue': 3, 'red': 2, 'yellow': 1})
+>>> counter.most_common()[0]
+('blue', 3)
+
+ +

#Set

<set> = set()                                   # {} returns a dictionary.
+
+ +
<set>.add(<el>)                                 # Or: <set> |= {<el>}
+<set>.update(<collection> [, ...])              # Or: <set> |= <set>
+
+
<set>  = <set>.union(<coll.>)                   # Or: <set> | <set>
+<set>  = <set>.intersection(<coll.>)            # Or: <set> & <set>
+<set>  = <set>.difference(<coll.>)              # Or: <set> - <set>
+<set>  = <set>.symmetric_difference(<coll.>)    # Or: <set> ^ <set>
+<bool> = <set>.issubset(<coll.>)                # Or: <set> <= <set>
+<bool> = <set>.issuperset(<coll.>)              # Or: <set> >= <set>
+
+
<el> = <set>.pop()                              # Raises KeyError if empty.
+<set>.remove(<el>)                              # Raises KeyError if missing.
+<set>.discard(<el>)                             # Doesn't raise an error.
+
+

Frozen Set

<frozenset> = frozenset(<collection>)
+
+ + +

#Tuple

Tuple is an immutable and hashable list.

<tuple> = ()                                # Or: tuple()
+<tuple> = (<el>,)                           # Or: <el>,
+<tuple> = (<el_1>, <el_2> [, ...])          # Or: <el_1>, <el_2> [, ...]
+
+ + +

Named Tuple

Tuple's subclass with named elements.

>>> from collections import namedtuple
+>>> Point = namedtuple('Point', 'x y')
+>>> p = Point(1, y=2)
+Point(x=1, y=2)
+>>> p[0]
+1
+>>> p.x
+1
+>>> getattr(p, 'y')
+2
+>>> p._fields  # Or: Point._fields
+('x', 'y')
+
+ + +

#Range

<range> = range(to_exclusive)
+<range> = range(from_inclusive, to_exclusive)
+<range> = range(from_inclusive, to_exclusive, ±step_size)
+
+ +
from_inclusive = <range>.start
+to_exclusive   = <range>.stop
+
+

#Enumerate

for i, el in enumerate(<collection> [, i_start]):
+    ...
+
+ +

#Iterator

<iter> = iter(<collection>)                 # `iter(<iter>)` returns unmodified iterator.
+<iter> = iter(<function>, to_exclusive)     # A sequence of return values until 'to_exclusive'.
+<el>   = next(<iter> [, default])           # Raises StopIteration or returns 'default' on end.
+<list> = list(<iter>)                       # Returns a list of iterator's remaining elements.
+
+ +

Itertools

from itertools import count, repeat, cycle, chain, islice
+
+ +
<iter> = count(start=0, step=1)             # Returns updated value endlessly. Accepts floats.
+<iter> = repeat(<el> [, times])             # Returns element endlessly or 'times' times.
+<iter> = cycle(<collection>)                # Repeats the sequence endlessly.
+
+
<iter> = chain(<coll_1>, <coll_2> [, ...])  # Empties collections in order (figuratively).
+<iter> = chain.from_iterable(<collection>)  # Empties collections inside a collection in order.
+
+
<iter> = islice(<coll>, to_exclusive)       # Only returns first 'to_exclusive' elements.
+<iter> = islice(<coll>, from_inclusive, …)  # `to_exclusive, step_size`.
+
+

#Generator

def count(start, step):
+    while True:
+        yield start
+        start += step
+
+ + +
>>> counter = count(10, 2)
+>>> next(counter), next(counter), next(counter)
+(10, 12, 14)
+
+

#Type

<type> = type(<el>)                          # Or: <el>.__class__
+<bool> = isinstance(<el>, <type>)            # Or: issubclass(type(<el>), <type>)
+
+ + +
>>> type('a'), 'a'.__class__, str
+(<class 'str'>, <class 'str'>, <class 'str'>)
+
+

Some types do not have built-in names, so they must be imported:

from types import FunctionType, MethodType, LambdaType, GeneratorType, ModuleType
+
+ +

Abstract Base Classes

Each abstract base class specifies a set of virtual subclasses. These classes are then recognized by isinstance() and issubclass() as subclasses of the ABC, although they are really not. ABC can also manually decide whether or not a specific class is its virtual subclass, usually based on which methods the class has implemented. For instance, Iterable ABC looks for method iter(), while Collection ABC looks for iter(), contains() and len().

>>> from collections.abc import Iterable, Collection, Sequence
+>>> isinstance([1, 2, 3], Iterable)
+True
+
+ + +
┏━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┓
+┃                  │  Iterable  │ Collection │  Sequence  ┃
+┠──────────────────┼────────────┼────────────┼────────────┨
+┃ list, range, str │     ✓      │     ✓      │     ✓      ┃
+┃ dict, set        │     ✓      │     ✓      │            ┃
+┃ iter             │     ✓      │            │            ┃
+┗━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┛
+
+
>>> from numbers import Number, Complex, Real, Rational, Integral
+>>> isinstance(123, Number)
+True
+
+
┏━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┓
+┃                    │  Number  │  Complex │   Real   │ Rational │ Integral ┃
+┠────────────────────┼──────────┼──────────┼──────────┼──────────┼──────────┨
+┃ int                │    ✓     │    ✓     │    ✓     │    ✓     │    ✓     ┃
+┃ fractions.Fraction │    ✓     │    ✓     │    ✓     │    ✓     │          ┃
+┃ float              │    ✓     │    ✓     │    ✓     │          │          ┃
+┃ complex            │    ✓     │    ✓     │          │          │          ┃
+┃ decimal.Decimal    │    ✓     │          │          │          │          ┃
+┗━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┛
+
+

#String

<str>  = <str>.strip()                       # Strips all whitespace characters from both ends.
+<str>  = <str>.strip('<chars>')              # Strips all passed characters from both ends.
+
+ +
<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>.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.
+
+
<bool> = <sub_str> in <str>                  # Checks if string contains a substring.
+<bool> = <str>.startswith(<sub_str>)         # Pass tuple of strings for multiple options.
+<bool> = <str>.endswith(<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 missing.
+
+
<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.
+
+
<str>  = chr(<int>)                          # Converts int to Unicode character.
+<int>  = ord(<str>)                          # Converts Unicode character to int.
+
+ +

Property Methods

┏━━━━━━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┓
+┃               │ [ !#$%…] │ [a-zA-Z] │  [¼½¾]   │  [²³¹]   │  [0-9]   ┃
+┠───────────────┼──────────┼──────────┼──────────┼──────────┼──────────┨
+┃ isprintable() │    ✓     │    ✓     │    ✓     │    ✓     │    ✓     ┃
+┃ isalnum()     │          │    ✓     │    ✓     │    ✓     │    ✓     ┃
+┃ isnumeric()   │          │          │    ✓     │    ✓     │    ✓     ┃
+┃ isdigit()     │          │          │          │    ✓     │    ✓     ┃
+┃ isdecimal()   │          │          │          │          │    ✓     ┃
+┗━━━━━━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┛
+
+ + +

#Regex

import re
+<str>   = re.sub(<regex>, new, text, count=0)  # Substitutes all occurrences with 'new'.
+<list>  = re.findall(<regex>, text)            # Returns all occurrences as strings.
+<list>  = re.split(<regex>, text, maxsplit=0)  # Use brackets in regex to include the matches.
+<Match> = re.search(<regex>, text)             # Searches for first occurrence of the pattern.
+<Match> = re.match(<regex>, text)              # Searches only at the beginning of the text.
+<iter>  = re.finditer(<regex>, text)           # Returns all occurrences as Match objects.
+
+ + +

Match Object

<str>   = <Match>.group()                      # Returns the whole match. Also group(0).
+<str>   = <Match>.group(1)                     # Returns part in the first bracket.
+<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.
+
+ +

Special Sequences

'\d' == '[0-9]'                                # Matches decimal characters.
+'\w' == '[a-zA-Z0-9_]'                         # Matches alphanumerics and underscore.
+'\s' == '[ \t\n\r\f\v]'                        # Matches whitespaces.
+
+ + +

#Format

<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> = '%s, %s' % (<el_1>, <el_2>)      # Redundant and inferior C style formatting.
+
+ +

Attributes

>>> Person = collections.namedtuple('Person', 'name height')
+>>> person = Person('Jean-Luc', 187)
+>>> f'{person.height}'
+'187'
+>>> '{p.height}'.format(p=person)
+'187'
+
+ +

General Options

{<el>:<10}                               # '<el>      '
+{<el>:^10}                               # '   <el>   '
+{<el>:>10}                               # '      <el>'
+{<el>:.<10}                              # '<el>......'
+{<el>:0}                                 # '<el>'
+
+ + +

Strings

{'abcde':10}                             # 'abcde     '
+{'abcde':10.3}                           # 'abc       '
+{'abcde':.3}                             # 'abc'
+{'abcde'!r:10}                           # "'abcde'   "
+
+ +

Numbers

{123456:10}                              # '    123456'
+{123456:10,}                             # '   123,456'
+{123456:10_}                             # '   123_456'
+{123456:+10}                             # '   +123456'
+{123456:=+10}                            # '+   123456'
+{123456: }                               # ' 123456'
+{-123456: }                              # '-123456'
+
+ +

Floats

{1.23456:10.3}                           # '      1.23'
+{1.23456:10.3f}                          # '     1.235'
+{1.23456:10.3e}                          # ' 1.235e+00'
+{1.23456:10.3%}                          # '  123.456%'
+
+ +

Comparison of presentation types:

┏━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┓
+┃              │    {<float>}   │   {<float>:f}  │   {<float>:e}  │   {<float>:%}  ┃
+┠──────────────┼────────────────┼────────────────┼────────────────┼────────────────┨
+┃  0.000056789 │   '5.6789e-05' │    '0.000057'  │ '5.678900e-05' │    '0.005679%' ┃
+┃  0.00056789  │   '0.00056789' │    '0.000568'  │ '5.678900e-04' │    '0.056789%' ┃
+┃  0.0056789   │   '0.0056789'  │    '0.005679'  │ '5.678900e-03' │    '0.567890%' ┃
+┃  0.056789    │   '0.056789'   │    '0.056789'  │ '5.678900e-02' │    '5.678900%' ┃
+┃  0.56789     │   '0.56789'    │    '0.567890'  │ '5.678900e-01' │   '56.789000%' ┃
+┃  5.6789      │   '5.6789'     │    '5.678900'  │ '5.678900e+00' │  '567.890000%' ┃
+┃ 56.789       │  '56.789'      │   '56.789000'  │ '5.678900e+01' │ '5678.900000%' ┃
+┗━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┛
+
+┏━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┓
+┃              │  {<float>:.2}  │  {<float>:.2f} │  {<float>:.2e} │  {<float>:.2%} ┃
+┠──────────────┼────────────────┼────────────────┼────────────────┼────────────────┨
+┃  0.000056789 │    '5.7e-05'   │      '0.00'    │   '5.68e-05'   │      '0.01%'   ┃
+┃  0.00056789  │    '0.00057'   │      '0.00'    │   '5.68e-04'   │      '0.06%'   ┃
+┃  0.0056789   │    '0.0057'    │      '0.01'    │   '5.68e-03'   │      '0.57%'   ┃
+┃  0.056789    │    '0.057'     │      '0.06'    │   '5.68e-02'   │      '5.68%'   ┃
+┃  0.56789     │    '0.57'      │      '0.57'    │   '5.68e-01'   │     '56.79%'   ┃
+┃  5.6789      │    '5.7'       │      '5.68'    │   '5.68e+00'   │    '567.89%'   ┃
+┃ 56.789       │    '5.7e+01'   │     '56.79'    │   '5.68e+01'   │   '5678.90%'   ┃
+┗━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┛
+
+ + + +

Ints

{90:c}                                   # 'Z'
+{90:b}                                   # '1011010'
+{90:X}                                   # '5A'
+
+ +

#Numbers

<int>      = int(<float/str/bool>)       # Or: math.floor(<float>)
+<float>    = float(<int/str/bool>)       # Or: <real>e±<int>
+<complex>  = complex(real=0, imag=0)     # Or: <real> ± <real>j
+<Fraction> = fractions.Fraction(0, 1)    # Or: Fraction(numerator=0, denominator=1)
+<Decimal>  = decimal.Decimal(<str/int>)  # Or: Decimal((sign, digits, exponent))
+
+ + +

Basic Functions

<num> = pow(<num>, <num>)                # Or: <num> ** <num>
+<num> = abs(<num>)                       # <float> = abs(<complex>)
+<num> = round(<num> [, ±ndigits])        # `round(126, -1) == 130`
+
+ +

Math

from math import e, pi, inf, nan, isinf, isnan
+from math import sin, cos, tan, asin, acos, atan, degrees, radians
+from math import log, log10, log2
+
+ +

Statistics

from statistics import mean, median, variance, stdev, quantiles, groupby
+
+ +

Random

from random import random, randint, choice, shuffle, gauss, 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.
+
+ +

Bin, Hex

<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>'.
+
+ +

Bitwise Operators

<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.
+
+ +

#Combinatorics

from itertools import product, combinations, combinations_with_replacement, permutations
+
+ + +
>>> product([0, 1], repeat=3)
+[(0, 0, 0), (0, 0, 1), (0, 1, 0), (0, 1, 1), ..., (1, 1, 1)]
+
+
>>> 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
+
+
>>> combinations('abc', 2)                   #   a  b  c
+[('a', 'b'), ('a', 'c'),                     # a .  x  x
+ ('b', 'c')]                                 # b .  .  x
+
+
>>> 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
+
+
>>> 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  .
+
+

#Datetime

from datetime import date, time, datetime, timedelta
+from dateutil.tz import UTC, tzlocal, gettz, datetime_exists, resolve_imaginary
+
+ + +

Constructors

<D>  = date(year, month, day)
+<T>  = time(hour=0, minute=0, second=0, microsecond=0, tzinfo=None, fold=0)
+<DT> = datetime(year, month, day, hour=0, minute=0, second=0, ...)
+<TD> = timedelta(weeks=0, days=0, hours=0, minutes=0, seconds=0, ...)
+
+ + +

Now

<D/DTn>  = D/DT.today()                     # Current local date or naive datetime.
+<DTn>    = DT.utcnow()                      # Naive datetime from current UTC time.
+<DTa>    = DT.now(<tzinfo>)                 # Aware datetime from current tz time.
+
+ + +

Timezone

<tzinfo> = UTC                              # UTC timezone. London without DST.
+<tzinfo> = tzlocal()                        # Local timezone. Also gettz().
+<tzinfo> = gettz('<Continent>/<City>')      # 'Continent/City_Name' timezone or None.
+<DTa>    = <DT>.astimezone(<tzinfo>)        # Datetime, converted to the passed timezone.
+<Ta/DTa> = <T/DT>.replace(tzinfo=<tzinfo>)  # Unconverted object with a new timezone.
+
+ +

Encode

<D/T/DT> = D/T/DT.fromisoformat('<iso>')    # Object from ISO string. Raises ValueError.
+<DT>     = DT.strptime(<str>, '<format>')   # Datetime from str, according to format.
+<D/DTn>  = D/DT.fromordinal(<int>)          # D/DTn from days since the Gregorian NYE 1.
+<DTn>    = DT.fromtimestamp(<real>)         # Local time DTn from seconds since the Epoch.
+<DTa>    = DT.fromtimestamp(<real>, <tz.>)  # Aware datetime from seconds since the Epoch.
+
+ + +

Decode

<str>    = <D/T/DT>.isoformat(sep='T')      # Also timespec='auto/hours/minutes/seconds/…'.
+<str>    = <D/T/DT>.strftime('<format>')    # Custom string representation.
+<int>    = <D/DT>.toordinal()               # Days since Gregorian NYE 1, ignoring time and tz.
+<float>  = <DTn>.timestamp()                # Seconds since the Epoch, from DTn in local tz.
+<float>  = <DTa>.timestamp()                # Seconds since the Epoch, from aware datetime.
+
+ +

Format

>>> dt = datetime.strptime('2015-05-14 23:39:00.00 +2000', '%Y-%m-%d %H:%M:%S.%f %z')
+>>> dt.strftime("%A, %dth of %B '%y, %I:%M%p %Z")
+"Thursday, 14th of May '15, 11:39PM UTC+02:00"
+
+ + +

Arithmetics

<D/DT>   = <D/DT>  ± <TD>                   # Returned datetime can fall into missing hour.
+<TD>     = <D/DTn> - <D/DTn>                # Returns the difference, ignoring time jumps.
+<TD>     = <DTa>   - <DTa>                  # Ignores time jumps if they share tzinfo object.
+<TD>     = <TD>    * <real>                 # Also: <TD> = abs(<TD>) and <TD> = <TD> ±% <TD>.
+<float>  = <TD>    / <TD>                   # How many weeks/years there are in TD. Also //.
+
+ +

#Arguments

Inside Function Call

func(<positional_args>)                           # func(0, 0)
+func(<keyword_args>)                              # func(x=0, y=0)
+func(<positional_args>, <keyword_args>)           # func(0, y=0)
+
+ + +

Inside Function Definition

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): ...
+
+ + +

#Splat Operator

Inside Function Call

Splat expands a collection into positional arguments, while splatty-splat expands a dictionary into keyword arguments.

args   = (1, 2)
+kwargs = {'x': 3, 'y': 4, 'z': 5}
+func(*args, **kwargs)
+
+ + + +

Is the same as:

func(1, 2, x=3, y=4, z=5)
+
+ +

Inside Function Definition

Splat combines zero or more positional arguments into a tuple, while splatty-splat combines zero or more keyword arguments into a dictionary.

def add(*a):
+    return sum(a)
+
+ + +
>>> add(1, 2, 3)
+6
+
+

Legal argument combinations:

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)
+
+ +
def f(*args): ...               # f(1, 2, 3)
+def f(x, *args): ...            # f(1, 2, 3)
+def f(*args, z): ...            # f(1, 2, z=3)
+
+
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)
+def f(*, x, **kwargs): ...      # f(x=1, y=2, z=3)
+
+
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)
+
+

Other Uses

<list>  = [*<coll.> [, ...]]    # Or: list(<collection>) [+ ...]
+<tuple> = (*<coll.>, [...])     # Or: tuple(<collection>) [+ ...]
+<set>   = {*<coll.> [, ...]}    # Or: set(<collection>) [| ...]
+<dict>  = {**<dict> [, ...]}    # Or: dict(**<dict> [, ...])
+
+ +
head, *body, tail = <coll.>     # Head or tail can be omitted.
+
+

#Inline

Lambda

<func> = lambda: <return_value>                     # A single statement function.
+<func> = lambda <arg_1>, <arg_2>: <return_value>    # Also accepts default arguments.
+
+ + +

Comprehensions

<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}
+
+ +
>>> [l+r for l in 'abc' for r in 'abc']
+['aa', 'ab', 'ac', ..., 'cc']
+
+

Map, Filter, Reduce

<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
+
+ + +

Any, All

<bool> = any(<collection>)                          # Is `bool(el)` True for any element.
+<bool> = all(<collection>)                          # Is True for all elements or empty.
+
+ +

Conditional Expression

<obj> = <exp> if <condition> else <exp>             # Only one expression gets evaluated.
+
+ +
>>> [a if a else 'zero' for a in (0, 1, 2, 3)]
+['zero', 1, 2, 3]
+
+

Named Tuple, Enum, Dataclass

from collections import namedtuple
+Point = namedtuple('Point', 'x y')                  # Creates a tuple's subclass.
+point = Point(0, 0)                                 # Returns its instance.
+
+ +
from enum import Enum
+Direction = Enum('Direction', 'n e s w')            # Creates an enum.
+direction = Direction.n                             # Returns its member.
+
+
from dataclasses import make_dataclass
+Player = make_dataclass('Player', ['loc', 'dir'])   # Creates a class.
+player = Player(point, direction)                   # Returns its instance.
+
+

#Imports

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'.
+
+ + +

#Closure

We have/get a closure in Python when:

def get_multiplier(a):
+    def out(b):
+        return a * b
+    return out
+
+ + + +
>>> multiply_by_3 = get_multiplier(3)
+>>> multiply_by_3(10)
+30
+
+ +

Partial

from functools import partial
+<function> = partial(<function> [, <arg_1>, <arg_2>, ...])
+
+ +
>>> import operator as op
+>>> multiply_by_3 = partial(op.mul, 3)
+>>> multiply_by_3(10)
+30
+
+ +

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'.

def get_counter():
+    i = 0
+    def out():
+        nonlocal i
+        i += 1
+        return i
+    return out
+
+ + +
>>> counter = get_counter()
+>>> counter(), counter(), counter()
+(1, 2, 3)
+
+

#Decorator

@decorator_name
+def function_that_gets_passed_to_decorator():
+    ...
+
+ + +

Debugger Example

Decorator that prints function's name every time the function is called.

from functools import wraps
+
+def debug(func):
+    @wraps(func)
+    def out(*args, **kwargs):
+        print(func.__name__)
+        return func(*args, **kwargs)
+    return out
+
+@debug
+def add(x, y):
+    return x + y
+
+ + + +

LRU Cache

Decorator that caches function's return values. All function's arguments must be hashable.

from functools import lru_cache
+
+@lru_cache(maxsize=None)
+def fib(n):
+    return n if n < 2 else fib(n-2) + fib(n-1)
+
+ + + +

Parametrized Decorator

A decorator that accepts arguments and returns a normal decorator that accepts a function.

from functools import wraps
+
+def debug(print_result=False):
+    def decorator(func):
+        @wraps(func)
+        def out(*args, **kwargs):
+            result = func(*args, **kwargs)
+            print(func.__name__, result if print_result else '')
+            return result
+        return out
+    return decorator
+
+@debug(print_result=True)
+def add(x, y):
+    return x + y
+
+ + + +

#Class

class <name>:
+    def __init__(self, a):
+        self.a = a
+    def __repr__(self):
+        class_name = self.__class__.__name__
+        return f'{class_name}({self.a!r})'
+    def __str__(self):
+        return str(self.a)
+
+    @classmethod
+    def get_class_name(cls):
+        return cls.__name__
+
+ + +

Str() use cases:

print(<el>)
+f'{<el>}'
+logging.warning(<el>)
+csv.writer(<file>).writerow([<el>])
+raise Exception(<el>)
+
+ +

Repr() use cases:

print/str/repr([<el>])
+f'{<el>!r}'
+Z = dataclasses.make_dataclass('Z', ['a']); print/str/repr(Z(<el>))
+>>> <el>
+
+ +

Constructor Overloading

class <name>:
+    def __init__(self, a=None):
+        self.a = a
+
+ +

Inheritance

class Person:
+    def __init__(self, name, age):
+        self.name = name
+        self.age  = age
+
+class Employee(Person):
+    def __init__(self, name, age, staff_num):
+        super().__init__(name, age)
+        self.staff_num = staff_num
+
+ +

Multiple Inheritance

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:

+
>>> C.mro()
+[<class 'C'>, <class 'A'>, <class 'B'>, <class 'object'>]
+
+

Property

Pythonic way of implementing getters and setters.

class Person:
+    @property
+    def name(self):
+        return ' '.join(self._name)
+
+    @name.setter
+    def name(self, value):
+        self._name = value.split()
+
+ + +
>>> person = Person()
+>>> person.name = '\t Guido  van Rossum \n'
+>>> person.name
+'Guido van Rossum'
+
+

Dataclass

Decorator that automatically generates init(), repr() and eq() special methods.

from dataclasses import dataclass, field
+
+@dataclass(order=False, frozen=False)
+class <class_name>:
+    <attr_name_1>: <type>
+    <attr_name_2>: <type> = <default_value>
+    <attr_name_3>: list/dict/set = field(default_factory=list/dict/set)
+
+ + + +

Inline:

from dataclasses import make_dataclass
+<class> = make_dataclass('<class_name>', <coll_of_attribute_names>)
+<class> = make_dataclass('<class_name>', <coll_of_tuples>)
+<tuple> = ('<attr_name>', <type> [, <default_value>])
+ +

Rest of type annotations (CPython interpreter ignores them all):

def func(<arg_name>: <type> [= <obj>]) -> <type>: ...
+<var_name>: typing.List/Set/Iterable/Sequence/Optional[<type>]
+<var_name>: typing.Dict/Tuple/Union[<type>, ...]
+
+ +

Slots

Mechanism that restricts objects to attributes listed in 'slots' and significantly reduces their memory footprint.

class MyClassWithSlots:
+    __slots__ = ['a']
+    def __init__(self):
+        self.a = 1
+
+ + +

Copy

from copy import copy, deepcopy
+<object> = copy(<object>)
+<object> = deepcopy(<object>)
+
+ +

#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.
    • +
  • Ne() automatically works on any object that has eq() defined.
    • +
class MyComparable:
+    def __init__(self, a):
+        self.a = a
+    def __eq__(self, other):
+        if isinstance(other, type(self)):
+            return self.a == other.a
+        return NotImplemented
+
+ + + + +

Hashable

class MyHashable:
+    def __init__(self, a):
+        self._a = a
+    @property
+    def a(self):
+        return self._a
+    def __eq__(self, other):
+        if isinstance(other, type(self)):
+            return self.a == other.a
+        return NotImplemented
+    def __hash__(self):
+        return hash(self.a)
+
+ + +

Sortable

from functools import total_ordering
+
+@total_ordering
+class MySortable:
+    def __init__(self, a):
+        self.a = a
+    def __eq__(self, other):
+        if isinstance(other, type(self)):
+            return self.a == other.a
+        return NotImplemented
+    def __lt__(self, other):
+        if isinstance(other, type(self)):
+            return self.a < other.a
+        return NotImplemented
+
+ + +

Iterator

class Counter:
+    def __init__(self):
+        self.i = 0
+    def __next__(self):
+        self.i += 1
+        return self.i
+    def __iter__(self):
+        return self
+
+ + +
>>> counter = Counter()
+>>> next(counter), next(counter), next(counter)
+(1, 2, 3)
+
+

Python has many different iterator objects:

Callable

    +
  • All functions and classes have a call() method, hence are callable.
    • +
  • When this cheatsheet uses '<function>' as an argument, it actually means '<callable>'.
    • +
class Counter:
+    def __init__(self):
+        self.i = 0
+    def __call__(self):
+        self.i += 1
+        return self.i
+
+ + + + +
>>> counter = Counter()
+>>> counter(), counter(), counter()
+(1, 2, 3)
+
+

Context Manager

class MyOpen:
+    def __init__(self, filename):
+        self.filename = filename
+    def __enter__(self):
+        self.file = open(self.filename)
+        return self.file
+    def __exit__(self, exc_type, exception, traceback):
+        self.file.close()
+
+ + +
>>> with open('test.txt', 'w') as file:
+...     file.write('Hello World!')
+>>> with MyOpen('test.txt') as file:
+...     print(file.read())
+Hello World!
+
+

#Iterable Duck Types

Iterable

    +
  • Only required method is iter(). It should return an iterator of object's items.
    • +
  • Contains() automatically works on any object that has iter() defined.
    • +
class MyIterable:
+    def __init__(self, a):
+        self.a = a
+    def __iter__(self):
+        return iter(self.a)
+    def __contains__(self, el):
+        return el in self.a
+
+ + + +
>>> obj = MyIterable([1, 2, 3])
+>>> [el for el in obj]
+[1, 2, 3]
+>>> 1 in obj
+True
+
+

Collection

class MyCollection:
+    def __init__(self, a):
+        self.a = a
+    def __iter__(self):
+        return iter(self.a)
+    def __contains__(self, el):
+        return el in self.a
+    def __len__(self):
+        return len(self.a)
+
+ + +

Sequence

class MySequence:
+    def __init__(self, a):
+        self.a = a
+    def __iter__(self):
+        return iter(self.a)
+    def __contains__(self, el):
+        return el in self.a
+    def __len__(self):
+        return len(self.a)
+    def __getitem__(self, i):
+        return self.a[i]
+    def __reversed__(self):
+        return reversed(self.a)
+
+ + +

Discrepancies between glossary definitions and abstract base classes:

+ + + + +

ABC Sequence

from collections import abc
+
+class MyAbcSequence(abc.Sequence):
+    def __init__(self, a):
+        self.a = a
+    def __len__(self):
+        return len(self.a)
+    def __getitem__(self, i):
+        return self.a[i]
+

Table of required and automatically available special methods:

┏━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━┓
+┃            │  Iterable  │ Collection │  Sequence  │ abc.Sequence ┃
+┠────────────┼────────────┼────────────┼────────────┼──────────────┨
+┃ iter()     │     !      │     !      │     ✓      │      ✓       ┃
+┃ contains() │     ✓      │     ✓      │     ✓      │      ✓       ┃
+┃ len()      │            │     !      │     !      │      !       ┃
+┃ getitem()  │            │            │     !      │      !       ┃
+┃ reversed() │            │            │     ✓      │      ✓       ┃
+┃ index()    │            │            │            │      ✓       ┃
+┃ count()    │            │            │            │      ✓       ┃
+┗━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━┛
+
+ + +

#Enum

from enum import Enum, auto
+
+ +
class <enum_name>(Enum):
+    <member_name_1> = <value_1>
+    <member_name_2> = <value_2_a>, <value_2_b>
+    <member_name_3> = auto()
+
+ +
<member> = <enum>.<member_name>                 # Returns a member.
+<member> = <enum>['<member_name>']              # Returns a member or raises KeyError.
+<member> = <enum>(<value>)                      # Returns a member or raises ValueError.
+<str>    = <member>.name                        # Returns member's name.
+<obj>    = <member>.value                       # Returns member's value.
+
+
list_of_members = list(<enum>)
+member_names    = [a.name for a in <enum>]
+member_values   = [a.value for a in <enum>]
+random_member   = random.choice(list(<enum>))
+
+
def get_next_member(member):
+    members = list(member.__class__)
+    index   = (members.index(member) + 1) % len(members)
+    return members[index]
+
+

Inline

Cutlery = Enum('Cutlery', 'fork knife spoon')
+Cutlery = Enum('Cutlery', ['fork', 'knife', 'spoon'])
+Cutlery = Enum('Cutlery', {'fork': 1, 'knife': 2, 'spoon': 3})
+
+ +

User-defined functions cannot be values, so they must be wrapped:

from functools import partial
+LogicOp = Enum('LogicOp', {'AND': partial(lambda l, r: l and r),
+                           'OR':  partial(lambda l, r: l or r)})
+
+ + +

#Exceptions

Basic Example

try:
+    <code>
+except <exception>:
+    <code>
+
+ + +

Complex Example

try:
+    <code_1>
+except <exception_a>:
+    <code_2_a>
+except <exception_b>:
+    <code_2_b>
+else:
+    <code_2_c>
+finally:
+    <code_3>
+
+ + +

Catching Exceptions

except <exception>:
+except <exception> as <name>:
+except (<exception>, [...]):
+except (<exception>, [...]) as <name>:
+
+ + +

Raising Exceptions

raise <exception>
+raise <exception>()
+raise <exception>(<el> [, ...])
+
+ +

Re-raising caught exception:

except <exception> as <name>:
+    ...
+    raise
+
+ +

Exception Object

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)
+traceback = ''.join(traceback.format_tb(<name>.__traceback__))
+error_msg = ''.join(traceback.format_exception(exc_type, <name>, <name>.__traceback__))
+
+ +

Built-in Exceptions

BaseException
+ ├── SystemExit                   # Raised by the sys.exit() function.
+ ├── KeyboardInterrupt            # Raised when the user hits the interrupt key (ctrl-c).
+ └── Exception                    # User-defined exceptions should be derived from this class.
+      ├── ArithmeticError         # Base class for arithmetic errors.
+      │    └── ZeroDivisionError  # Raised when dividing by zero.
+      ├── AssertionError          # Raised by `assert <exp>` if expression returns false value.
+      ├── AttributeError          # Raised when an attribute is missing.
+      ├── EOFError                # Raised by input() when it hits end-of-file condition.
+      ├── LookupError             # Raised when a look-up on a collection fails.
+      │    ├── IndexError         # Raised when a sequence index is out of range.
+      │    └── KeyError           # Raised when a dictionary key or set element is missing.
+      ├── MemoryError             # Out of memory. Could be too late to start deleting vars.
+      ├── NameError               # Raised when an object is missing.
+      ├── OSError                 # Errors such as “file not found” or “disk full” (see Open).
+      │    └── FileNotFoundError  # When a file or directory is requested but doesn't exist.
+      ├── RuntimeError            # Raised by errors that don't fall into other categories.
+      │    └── RecursionError     # Raised when the maximum recursion depth is exceeded.
+      ├── StopIteration           # Raised by next() when run on an empty iterator.
+      ├── TypeError               # Raised when an argument is of wrong type.
+      └── ValueError              # When an argument is of right type but inappropriate value.
+           └── UnicodeError       # Raised when encoding/decoding strings to/from bytes fails.
+
+ +

Collections and their exceptions:

┏━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┓
+┃           │    List    │    Set     │    Dict    ┃
+┠───────────┼────────────┼────────────┼────────────┨
+┃ getitem() │ IndexError │            │  KeyError  ┃
+┃ pop()     │ IndexError │  KeyError  │  KeyError  ┃
+┃ remove()  │ ValueError │  KeyError  │            ┃
+┃ index()   │ ValueError │            │            ┃
+┗━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┛
+
+ +

Useful built-in exceptions:

raise TypeError('Argument is of wrong type!')
+raise ValueError('Argument is of right type but inappropriate value!')
+raise RuntimeError('None of above!')
+
+ +

User-defined Exceptions

class MyError(Exception): pass
+class MyInputError(MyError): pass
+
+ +

#Exit

Exits the interpreter by raising SystemExit exception.

import sys
+sys.exit()                        # Exits with exit code 0 (success).
+sys.exit(<el>)                    # Prints to stderr and exits with 1.
+sys.exit(<int>)                   # Exits with passed exit code.
+
+ + +

#Print

print(<el_1>, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
+
+ + +

Pretty Print

from pprint import pprint
+pprint(<collection>, width=80, depth=None, compact=False, sort_dicts=True)
+
+ + +

#Input

Reads a line from user input or pipe if present.

<str> = input(prompt=None)
+
+ + + +

#Command Line Arguments

import sys
+scripts_path = sys.argv[0]
+arguments    = sys.argv[1:]
+
+ +

Argument Parser

from argparse import ArgumentParser, FileType
+p = ArgumentParser(description=<str>)
+p.add_argument('-<short_name>', '--<name>', action='store_true')  # Flag.
+p.add_argument('-<short_name>', '--<name>', type=<type>)          # Option.
+p.add_argument('<name>', type=<type>, nargs=1)                    # First argument.
+p.add_argument('<name>', type=<type>, nargs='+')                  # Remaining arguments.
+p.add_argument('<name>', type=<type>, nargs='*')                  # Optional arguments.
+args  = p.parse_args()                                            # Exits on error.
+value = args.<name>
+
+ + +

#Open

Opens the file and returns a corresponding file object.

<file> = open(<path>, mode='r', encoding=None, newline=None)
+
+ + + +

Modes

Exceptions

    +
  • 'FileNotFoundError' can be raised when reading with 'r' or 'r+'.
    • +
  • 'FileExistsError' can be raised when writing with 'x'.
    • +
  • 'IsADirectoryError' and 'PermissionError' can be raised by any.
    • +
  • 'OSError' is the parent class of all listed exceptions.
    • +

File Object

<file>.seek(0)                      # Moves to the start of the file.
+<file>.seek(offset)                 # Moves 'offset' chars/bytes from the start.
+<file>.seek(0, 2)                   # Moves to the end of the file.
+<bin_file>.seek(±offset, <anchor>)  # Anchor: 0 start, 1 current position, 2 end.
+
+ + + + + +
<str/bytes> = <file>.read(size=-1)  # Reads 'size' chars/bytes or until 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.
+
+
<file>.write(<str/bytes>)           # Writes a string or bytes object.
+<file>.writelines(<collection>)     # Writes a coll. of strings or bytes objects.
+<file>.flush()                      # Flushes write buffer. Runs every 4096/8192 B.
+
+ +

Read Text from File

def read_file(filename):
+    with open(filename, encoding='utf-8') as file:
+        return file.readlines()
+
+ +

Write Text to File

def write_to_file(filename, text):
+    with open(filename, 'w', encoding='utf-8') as file:
+        file.write(text)
+
+ +

#Paths

from os import getcwd, path, listdir, scandir
+from glob import glob
+
+ +
<str>  = getcwd()                   # Returns the current working directory.
+<str>  = path.join(<path>, ...)     # Joins two or more pathname components.
+<str>  = path.abspath(<path>)       # Returns absolute path.
+
+
<str>  = path.basename(<path>)      # Returns final component of the path.
+<str>  = path.dirname(<path>)       # Returns path without the final component.
+<tup.> = path.splitext(<path>)      # Splits on last period of the final component.
+
+
<list> = listdir(path='.')          # Returns filenames located at path.
+<list> = glob('<pattern>')          # Returns paths matching the wildcard pattern.
+
+
<bool> = path.exists(<path>)        # Or: <Path>.exists()
+<bool> = path.isfile(<path>)        # Or: <DirEntry/Path>.is_file()
+<bool> = path.isdir(<path>)         # Or: <DirEntry/Path>.is_dir()
+
+
<stat> = os.stat(<path>)            # Or: <DirEntry/Path>.stat()
+<real> = <stat>.st_mtime/st_size/…  # Modification time, size in bytes, …
+
+

DirEntry

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.

<iter> = scandir(path='.')          # Returns DirEntry objects located at path.
+<str>  = <DirEntry>.path            # Returns 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.
+
+ + +

Path Object

from pathlib import Path
+
+ +
<Path> = Path(<path> [, ...])       # Accepts strings, Paths and DirEntry objects.
+<Path> = <path> / <path> [/ ...]    # First or second path must be a Path object.
+
+
<Path> = Path()                     # Returns relative cwd. 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>.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.
+
+
<iter> = <Path>.iterdir()           # Returns directory contents as Path objects.
+<iter> = <Path>.glob('<pattern>')   # Returns Paths matching the wildcard pattern.
+
+
<str>  = str(<Path>)                # Returns path as a string.
+<file> = open(<Path>)               # Also <Path>.read/write_text/bytes().
+
+

#OS Commands

import os, shutil, subprocess
+
+ +
os.chdir(<path>)                 # Changes the current working directory.
+os.mkdir(<path>, mode=0o777)     # Creates a directory. Mode is in octal.
+os.makedirs(<path>, mode=0o777)  # Creates all path's dirs. Also: `exist_ok=False`.
+
+
shutil.copy(from, to)            # Copies the file. 'to' can exist or be a dir.
+shutil.copytree(from, to)        # Copies the directory. 'to' must not exist.
+
+
os.rename(from, to)              # Renames/moves the file or directory.
+os.replace(from, to)             # Same, but overwrites 'to' if it exists.
+
+
os.remove(<path>)                # Deletes the file.
+os.rmdir(<path>)                 # Deletes the empty directory.
+shutil.rmtree(<path>)            # Deletes the directory.
+
+ +

Shell Commands

<pipe> = os.popen('<command>')   # Executes command in sh/cmd and returns its stdout pipe.
+<str>  = <pipe>.read(size=-1)    # Reads 'size' chars or until EOF. Also readline/s().
+<int>  = <pipe>.close()          # Closes the pipe. Returns None on success, int on error.
+
+ +

Sends '1 + 1' to the basic calculator and captures its output:

>>> subprocess.run('bc', input='1 + 1\n', capture_output=True, text=True)
+CompletedProcess(args='bc', returncode=0, stdout='2\n', stderr='')
+
+ +

Sends test.in to the basic calculator running in standard mode and saves its output to test.out:

>>> from shlex import split
+>>> os.popen('echo 1 + 1 > test.in')
+>>> subprocess.run(split('bc -s'), stdin=open('test.in'), stdout=open('test.out', 'w'))
+CompletedProcess(args=['bc', '-s'], returncode=0)
+>>> open('test.out').read()
+'2\n'
+
+ +

#JSON

Text file format for storing collections of strings and numbers.

import json
+<str>    = json.dumps(<object>)    # Converts object to JSON string.
+<object> = json.loads(<str>)       # Converts JSON string to object.
+
+ + +

Read Object from JSON File

def read_json_file(filename):
+    with open(filename, encoding='utf-8') as file:
+        return json.load(file)
+
+ +

Write Object to JSON File

def write_to_json_file(filename, an_object):
+    with open(filename, 'w', encoding='utf-8') as file:
+        json.dump(an_object, file, ensure_ascii=False, indent=2)
+
+ +

#Pickle

Binary file format for storing Python objects.

import pickle
+<bytes>  = pickle.dumps(<object>)  # Converts object to bytes.
+<object> = pickle.loads(<bytes>)   # Converts bytes to object.
+
+ + +

Read Object from File

def read_pickle_file(filename):
+    with open(filename, 'rb') as file:
+        return pickle.load(file)
+
+ +

Write Object to File

def write_to_pickle_file(filename, an_object):
+    with open(filename, 'wb') as file:
+        pickle.dump(an_object, file)
+
+ +

#CSV

Text file format for storing spreadsheets.

import csv
+
+ + +

Read

<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.
+
+ + +

Write

<writer> = csv.writer(<file>)       # Also: `dialect='excel', delimiter=','`.
+<writer>.writerow(<collection>)     # Encodes objects using `str(<el>)`.
+<writer>.writerows(<coll_of_coll>)  # Appends multiple rows.
+
+ + +

Parameters

Dialects

┏━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┓
+┃                  │     excel    │   excel-tab  │     unix     ┃
+┠──────────────────┼──────────────┼──────────────┼──────────────┨
+┃ delimiter        │       ','    │      '\t'    │       ','    ┃
+┃ quotechar        │       '"'    │       '"'    │       '"'    ┃
+┃ doublequote      │      True    │      True    │      True    ┃
+┃ skipinitialspace │     False    │     False    │     False    ┃
+┃ lineterminator   │    '\r\n'    │    '\r\n'    │      '\n'    ┃
+┃ quoting          │         0    │         0    │         1    ┃
+┃ escapechar       │      None    │      None    │      None    ┃
+┗━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┛
+
+ + + +

Read Rows from CSV File

def read_csv_file(filename, dialect='excel'):
+    with open(filename, encoding='utf-8', newline='') as file:
+        return list(csv.reader(file, dialect))
+
+ +

Write Rows to CSV File

def write_to_csv_file(filename, rows, dialect='excel'):
+    with open(filename, 'w', encoding='utf-8', newline='') as file:
+        writer = csv.writer(file, dialect)
+        writer.writerows(rows)
+
+ +

#SQLite

A server-less database engine that stores each database into a separate file.

Connect

Opens a connection to the database file. Creates a new file if path doesn't exist.

import sqlite3
+<conn> = sqlite3.connect(<path>)                # Also ':memory:'.
+<conn>.close()                                  # Closes the connection.
+
+ + + + +

Read

Returned values can be of type str, int, float, bytes or None.

<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>).
+
+ + +

Write

<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:

with <conn>:                                    # Exits the block with commit() or rollback(),
+    <conn>.execute('<query>')                   # depending on whether any exception occurred.
+
+ +

Placeholders

<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.
+
+ + +

Example

Values are not actually saved in this example because 'conn.commit()' is omitted!

>>> 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()
+[(1, 'Jean-Luc', 187)]
+
+ + +

MySQL

Has a very similar interface, with differences listed below.

# $ pip3 install mysql-connector
+from mysql import connector
+<conn>   = connector.connect(host=<str>, …)     # `user=<str>, password=<str>, database=<str>`.
+<cursor> = <conn>.cursor()                      # Only cursor has execute() method.
+<cursor>.execute('<query>')                     # Can raise a subclass of connector.Error.
+<cursor>.execute('<query>', <list/tuple>)       # Replaces '%s's in query with values.
+<cursor>.execute('<query>', <dict/namedtuple>)  # Replaces '%(<key>)s's with values.
+
+ + +

#Bytes

Bytes object is an immutable sequence of single bytes. Mutable version is called bytearray.

<bytes> = b'<str>'                       # Only accepts ASCII characters and \x00-\xff.
+<int>   = <bytes>[<index>]               # Returns an int 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.
+
+ + +

Encode

<bytes> = bytes(<coll_of_ints>)          # Ints must be in range from 0 to 255.
+<bytes> = bytes(<str>, 'utf-8')          # Or: <str>.encode('utf-8')
+<bytes> = <int>.to_bytes(n_bytes, …)     # `byteorder='big/little', signed=False`.
+<bytes> = bytes.fromhex('<hex>')         # Hex pairs can be separated by whitespaces.
+
+ +

Decode

<list>  = list(<bytes>)                  # Returns ints in range from 0 to 255.
+<str>   = str(<bytes>, 'utf-8')          # Or: <bytes>.decode('utf-8')
+<int>   = int.from_bytes(<bytes>, …)     # `byteorder='big/little', signed=False`.
+'<hex>' = <bytes>.hex()                  # Returns hex pairs. Accepts `sep=<str>`.
+
+ +

Read Bytes from File

def read_bytes(filename):
+    with open(filename, 'rb') as file:
+        return file.read()
+
+ +

Write Bytes to File

def write_bytes(filename, bytes_obj):
+    with open(filename, 'wb') as file:
+        file.write(bytes_obj)
+
+ +

#Struct

from struct import pack, unpack
+<bytes> = pack('<format>', <el_1> [, ...])  # Packages arguments into bytes object.
+<tuple> = unpack('<format>', <bytes>)       # Use iter_unpack() for iterator of tuples.
+
+ + +
>>> pack('>hhl', 1, 2, 3)
+b'\x00\x01\x00\x02\x00\x00\x00\x03'
+>>> unpack('>hhl', b'\x00\x01\x00\x02\x00\x00\x00\x03')
+(1, 2, 3)
+
+

Format

For standard type sizes and manual alignment (padding) start format string with:

Besides numbers, pack() and unpack() also support bytes objects as part of the seqence:

    +
  • 'c' - A bytes object with a single element. Use 'x' for pad byte.
    • +
  • '<n>s' - A bytes object with n elements.
    • +

Integer types. Use a capital letter for unsigned type. Minimum and standard sizes are in brackets:

    +
  • 'b' - char (1/1)
    • +
  • 'h' - short (2/2)
    • +
  • 'i' - int (2/4)
    • +
  • 'l' - long (4/4)
    • +
  • 'q' - long long (8/8)
    • +

Floating point types:

    +
  • 'f' - float (4/4)
    • +
  • 'd' - double (8/8)
    • +
+ + + + + + + + +

#Array

List that can only hold numbers of a predefined type. Available types and their minimum sizes in bytes are listed above. Sizes and byte order are always determined by the system.

from array import array
+<array> = array('<typecode>', <collection>)    # Array from collection of numbers.
+<array> = array('<typecode>', <bytes>)         # Array from bytes object.
+<array> = array('<typecode>', <array>)         # Treats array as a sequence of numbers.
+<bytes> = bytes(<array>)                       # Or: <array>.tobytes()
+<file>.write(<array>)                          # Writes array to the binary file.
+
+ + +

#Memory View

<mview> = memoryview(<bytes/bytearray/array>)  # Immutable if bytes, else mutable.
+<real>  = <mview>[<index>]                     # Returns an int or a float.
+<mview> = <mview>[<slice>]                     # Mview with rearranged elements.
+<mview> = <mview>.cast('<typecode>')           # Casts memoryview to the new format.
+<mview>.release()                              # Releases the object's memory buffer.
+
+ + +

Decode

<bytes> = bytes(<mview>)                       # Creates a new bytes object.
+<bytes> = <bytes>.join(<coll_of_mviews>)       # Joins mviews using bytes object as sep.
+<array> = array('<typecode>', <mview>)         # Treats mview as a sequence of numbers.
+<file>.write(<mview>)                          # Writes mview to the binary file.
+
+ +
<list>  = list(<mview>)                        # Returns a list of ints or floats.
+<str>   = str(<mview>, 'utf-8')                # Treats mview as a bytes object.
+<int>   = int.from_bytes(<mview>, …)           # `byteorder='big/little', signed=False`.
+'<hex>' = <mview>.hex()                        # Treats mview as a bytes object.
+
+

#Deque

A thread-safe list with efficient appends and pops from either side. Pronounced "deck".

from collections import deque
+<deque> = deque(<collection>, maxlen=None)
+
+ + +
<deque>.appendleft(<el>)                       # Opposite element is dropped if full.
+<deque>.extendleft(<collection>)               # Collection gets reversed.
+<el> = <deque>.popleft()                       # Raises IndexError if empty.
+<deque>.rotate(n=1)                            # Rotates elements to the right.
+
+

#Threading

from threading import Thread, RLock, Semaphore, Event, Barrier
+from concurrent.futures import ThreadPoolExecutor
+
+ + +

Thread

<Thread> = Thread(target=<function>)           # Use `args=<collection>` to set the arguments.
+<Thread>.start()                               # Starts the thread.
+<bool> = <Thread>.is_alive()                   # Checks if the thread has finished executing.
+<Thread>.join()                                # Waits for the thread to finish.
+
+ + +

Lock

<lock> = RLock()                               # Lock that can only be released by the owner.
+<lock>.acquire()                               # Waits for the lock to be available.
+<lock>.release()                               # Makes the lock available again.
+
+ +

Or:

with <lock>:                                   # Enters the block by calling acquire(),
+    ...                                        # and exits it with release().
+
+ +

Semaphore, Event, Barrier

<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.
+
+ +

Thread Pool Executor

<Exec> = ThreadPoolExecutor(max_workers=None)  # Or: `with ThreadPoolExecutor() as <name>: …`
+<Exec>.shutdown(wait=True)                     # Blocks until all threads finish executing.
+
+ + +
<iter> = <Exec>.map(<func>, <args_1>, ...)     # A multithreaded and non-lazy map().
+<Futr> = <Exec>.submit(<func>, <arg_1>, ...)   # Starts a thread and returns its Future object.
+<bool> = <Futr>.done()                         # Checks if the thread has finished executing.
+<obj>  = <Futr>.result()                       # Waits for thread to finish and returns result.
+
+

Queue

A thread-safe FIFO queue. For LIFO queue use LifoQueue.

from queue import Queue
+<Queue> = Queue(maxsize=0)
+
+ + +
<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.
+
+

#Operator

Module of functions that provide the functionality of operators.

import operator as op
+<el>      = op.add/sub/mul/truediv/floordiv/mod(<el>, <el>)  # +, -, *, /, //, %
+<int/set> = op.and_/or_/xor(<int/set>, <int/set>)            # &, |, ^
+<bool>    = op.eq/ne/lt/le/gt/ge(<sortable>, <sortable>)     # ==, !=, <, <=, >, >=
+<func>    = op.itemgetter/attrgetter/methodcaller(<obj>)     # [index/key], .name, .name()
+
+ + +
elementwise_sum  = map(op.add, list_a, list_b)
+sorted_by_second = sorted(<collection>, key=op.itemgetter(1))
+sorted_by_both   = sorted(<collection>, key=op.itemgetter(1, 0))
+product_of_elems = functools.reduce(op.mul, <collection>)
+union_of_sets    = functools.reduce(op.or_, <coll_of_sets>)
+first_element    = op.methodcaller('pop', 0)(<list>)
+
+ +

#Introspection

Inspecting code at runtime.

Variables

<list> = dir()                             # Names of local variables (incl. functions).
+<dict> = vars()                            # Dict of local variables. Also locals().
+<dict> = globals()                         # Dict of global variables.
+
+ + + +

Attributes

<list> = dir(<object>)                     # Names of object's attributes (incl. methods).
+<dict> = vars(<object>)                    # Dict of writable attributes. Also <obj>.__dict__.
+<bool> = hasattr(<object>, '<attr_name>')  # Checks if getattr() raises an AttributeError.
+value  = getattr(<object>, '<attr_name>')  # Raises AttributeError if attribute is missing.
+setattr(<object>, '<attr_name>', value)    # Only works on objects with '__dict__' attribute.
+delattr(<object>, '<attr_name>')           # Same. Also `del <object>.<attr_name>`.
+
+ +

Parameters

from inspect import signature
+<Sig>  = signature(<function>)             # Function's Signature object.
+<dict> = <Sig>.parameters                  # Dict of function's Parameter objects.
+<str>  = <Param>.name                      # Parameter's name.
+<memb> = <Param>.kind                      # Member of ParameterKind enum.
+
+ +

#Metaprogramming

Code that generates code.

Type

Type is the root class. If only passed an object it returns its type (class). Otherwise it creates a new class.

<class> = type('<class_name>', <tuple_of_parents>, <dict_of_class_attributes>)
+ + + + +
>>> Z = type('Z', (), {'a': 'abcde', 'b': 12345})
+>>> z = Z()
+
+

Meta Class

A class that creates classes.

def my_meta_class(name, parents, attrs):
+    attrs['a'] = 'abcde'
+    return type(name, parents, attrs)
+
+ + +

Or:

class MyMetaClass(type):
+    def __new__(cls, name, parents, attrs):
+        attrs['a'] = 'abcde'
+        return type.__new__(cls, name, parents, attrs)
+
+ + +

Metaclass Attribute

Right before a class is created it checks if it has the 'metaclass' attribute defined. If not, it recursively checks if any of his parents has it defined and eventually comes to type().

class MyClass(metaclass=MyMetaClass):
+    b = 12345
+
+ + +
>>> MyClass.a, MyClass.b
+('abcde', 12345)
+
+

Type Diagram

type(MyClass) == MyMetaClass         # MyClass is an instance of MyMetaClass.
+type(MyMetaClass) == type            # MyMetaClass is an instance of type.
+
+ +
┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┓
+┃   Classes   │ Metaclasses ┃
+┠─────────────┼─────────────┨
+┃   MyClass ──→ MyMetaClass ┃
+┃             │     ↓       ┃
+┃    object ─────→ type ←╮  ┃
+┃             │     ↑ ╰──╯  ┃
+┃     str ──────────╯       ┃
+┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┛
+
+

Inheritance Diagram

MyClass.__base__ == object           # MyClass is a subclass of object.
+MyMetaClass.__base__ == type         # MyMetaClass is a subclass of type.
+
+ +
┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┓
+┃   Classes   │ Metaclasses ┃
+┠─────────────┼─────────────┨
+┃   MyClass   │ MyMetaClass ┃
+┃      ↓      │     ↓       ┃
+┃    object ←───── type     ┃
+┃      ↑      │             ┃
+┃     str     │             ┃
+┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┛
+
+

#Eval

>>> from ast import literal_eval
+>>> literal_eval('[1, 2, 3]')
+[1, 2, 3]
+>>> literal_eval('1 + 2')
+ValueError: malformed node or string
+
+ +

#Coroutines

Runs a terminal game where you control an asterisk that must avoid numbers:

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
+
+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.
+
+async def main_coroutine(screen):
+    state = {'*': P(0, 0), **{id_: P(W//2, H//2) for id_ in range(10)}}
+    moves = asyncio.Queue()
+    coros = (*(random_controller(id_, moves) for id_ in range(10)),
+             human_controller(screen, moves), model(moves, state), view(state, screen))
+    await asyncio.wait(coros, return_when=asyncio.FIRST_COMPLETED)
+
+async def random_controller(id_, moves):
+    while True:
+        d = random.choice(list(D))
+        moves.put_nowait((id_, d))
+        await asyncio.sleep(random.triangular(0.01, 0.65))
+
+async def human_controller(screen, moves):
+    while True:
+        ch = screen.getch()
+        key_mappings = {258: D.s, 259: D.n, 260: D.w, 261: D.e}
+        if ch in key_mappings:
+            moves.put_nowait(('*', key_mappings[ch]))
+        await asyncio.sleep(0.005)
+
+async def model(moves, state):
+    while state['*'] not in (state[id_] for id_ in range(10)):
+        id_, d = await moves.get()
+        x, y   = state[id_]
+        deltas = {D.n: P(0, -1), D.e: P(1, 0), D.s: P(0, 1), D.w: P(-1, 0)}
+        state[id_] = P((x + deltas[d].x) % W, (y + deltas[d].y) % H)
+
+async def view(state, screen):
+    offset = P(curses.COLS//2 - W//2, curses.LINES//2 - H//2)
+    while True:
+        screen.erase()
+        curses.textpad.rectangle(screen, offset.y-1, offset.x-1, offset.y+H, offset.x+W)
+        for id_, p in state.items():
+            screen.addstr(offset.y + (p.y - state['*'].y + H//2) % H,
+                          offset.x + (p.x - state['*'].x + W//2) % W, str(id_))
+        await asyncio.sleep(0.005)
+
+if __name__ == '__main__':
+    curses.wrapper(main)
+
+ + + +


+

Libraries

#Progress Bar

# $ pip3 install tqdm
+>>> from tqdm import tqdm
+>>> from time import sleep
+>>> for el in tqdm([1, 2, 3], desc='Processing'):
+...     sleep(1)
+Processing: 100%|████████████████████| 3/3 [00:03<00:00,  1.00s/it]
+
+ + +

#Plot

# $ pip3 install matplotlib
+import matplotlib.pyplot as plt
+plt.plot(<x_data>, <y_data> [, label=<str>])   # Or: plt.plot(<y_data>)
+plt.legend()                                   # Adds a legend.
+plt.savefig(<path>)                            # Saves the figure.
+plt.show()                                     # Displays the figure.
+plt.clf()                                      # Clears the figure.
+
+ +

#Table

Prints a CSV file as an ASCII table:

# $ pip3 install tabulate
+import csv, tabulate
+with open('test.csv', encoding='utf-8', newline='') as file:
+    rows   = csv.reader(file)
+    header = next(rows)
+    table  = tabulate.tabulate(rows, header)
+print(table)
+
+ + +

#Curses

Runs a basic file explorer in the terminal:

from curses import wrapper, ascii, A_REVERSE, KEY_DOWN, KEY_UP, KEY_LEFT, KEY_RIGHT, KEY_ENTER
+from os import listdir, path, chdir
+
+def main(screen):
+    ch, first, selected, paths = 0, 0, 0, listdir()
+    while ch != ascii.ESC:
+        height, _ = screen.getmaxyx()
+        screen.erase()
+        for y, filename in enumerate(paths[first : first+height]):
+            screen.addstr(y, 0, filename, A_REVERSE * (selected == first + y))
+        ch = screen.getch()
+        selected += (ch == KEY_DOWN) - (ch == KEY_UP)
+        selected = max(0, min(len(paths)-1, selected))
+        first += (first <= selected - height) - (first > selected)
+        if ch in [KEY_LEFT, KEY_RIGHT, KEY_ENTER, 10, 13]:
+            new_dir = '..' if ch == KEY_LEFT else paths[selected]
+            if path.isdir(new_dir):
+                chdir(new_dir)
+                first, selected, paths = 0, 0, listdir()
+
+if __name__ == '__main__':
+    wrapper(main)
+
+ + +

#Logging

# $ pip3 install loguru
+from loguru import logger
+
+ +
logger.add('debug_{time}.log', colorize=True)  # Connects a log file.
+logger.add('error_{time}.log', level='ERROR')  # Another file for errors or higher.
+logger.<level>('A logging message.')
+
+ +

Exceptions

Exception description, stack trace and values of variables are appended automatically.

try:
+    ...
+except <exception>:
+    logger.exception('An error happened.')
+
+ + +

Rotation

Argument that sets a condition when a new log file is created.

rotation=<int>|<datetime.timedelta>|<datetime.time>|<str>
+
+ + + +

Retention

Sets a condition which old log files get deleted.

retention=<int>|<datetime.timedelta>|<str>
+
+ + + +

#Scraping

Scrapes Python's URL, version number and logo from its Wikipedia page:

# $ pip3 install requests beautifulsoup4
+import requests, bs4, os, sys
+
+WIKI_URL = 'https://en.wikipedia.org/wiki/Python_(programming_language)'
+try:
+    html       = requests.get(WIKI_URL).text
+    document   = bs4.BeautifulSoup(html, 'html.parser')
+    table      = document.find('table', class_='infobox vevent')
+    python_url = table.find('th', text='Website').next_sibling.a['href']
+    version    = table.find('th', text='Stable release').next_sibling.strings.__next__()
+    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)
+    print(f'{python_url}, {version}, file://{os.path.abspath(filename)}')
+except requests.exceptions.ConnectionError:
+    print("You've got problems with connection.", file=sys.stderr)
+
+ + +

#Web

# $ pip3 install bottle
+from bottle import run, route, static_file, template, post, request, response
+import json
+
+ +

Run

run(host='localhost', port=8080)        # Runs locally.
+run(host='0.0.0.0', port=80)            # Runs globally.
+
+ +

Static Request

@route('/img/<filename>')
+def send_file(filename):
+    return static_file(filename, root='img_dir/')
+
+ +

Dynamic Request

@route('/<sport>')
+def send_html(sport):
+    return template('<h1>{{title}}</h1>', title=sport)
+
+ +

REST Request

@post('/<sport>/odds')
+def send_json(sport):
+    team = request.forms.get('team')
+    response.headers['Content-Type'] = 'application/json'
+    response.headers['Cache-Control'] = 'no-cache'
+    return json.dumps({'team': team, 'odds': [2.09, 3.74, 3.68]})
+
+ +

Test:

# $ pip3 install requests
+>>> import threading, requests
+>>> threading.Thread(target=run, daemon=True).start()
+>>> url = 'http://localhost:8080/football/odds'
+>>> request_data = {'team': 'arsenal f.c.'}
+>>> response = requests.post(url, data=request_data)
+>>> response.json()
+{'team': 'arsenal f.c.', 'odds': [2.09, 3.74, 3.68]}
+
+ +

#Profiling

Stopwatch

from time import time
+start_time = time()                     # Seconds since the Epoch.
+...
+duration = time() - start_time
+
+ + +

High performance:

from time import perf_counter
+start_time = perf_counter()             # Seconds since the restart.
+...
+duration = perf_counter() - start_time
+
+ +

Timing a Snippet

>>> from timeit import timeit
+>>> timeit("''.join(str(i) for i in range(100))",
+...        number=10000, globals=globals(), setup='pass')
+0.34986
+
+ +

Profiling by Line

# $ pip3 install line_profiler memory_profiler
+@profile
+def main():
+    a = [*range(10000)]
+    b = {*range(10000)}
+main()
+
+ +
$ kernprof -lv test.py
+Line #   Hits     Time  Per Hit   % Time  Line Contents
+=======================================================
+     1                                    @profile
+     2                                    def main():
+     3      1    955.0    955.0     43.7      a = [*range(10000)]
+     4      1   1231.0   1231.0     56.3      b = {*range(10000)}
+
+
$ python3 -m memory_profiler test.py
+Line #         Mem usage      Increment   Line Contents
+=======================================================
+     1        37.668 MiB     37.668 MiB   @profile
+     2                                    def main():
+     3        38.012 MiB      0.344 MiB       a = [*range(10000)]
+     4        38.477 MiB      0.465 MiB       b = {*range(10000)}
+
+

Call Graph

Generates a PNG image of the call graph with highlighted bottlenecks:

# $ pip3 install pycallgraph2; brew/apt install graphviz
+import pycallgraph2 as cg, datetime
+filename = f'profile-{datetime.datetime.now():%Y%m%d%H%M%S}.png'
+drawer = cg.output.GraphvizOutput(output_file=filename)
+with cg.PyCallGraph(drawer):
+    <code_to_be_profiled>
+
+ + +

#NumPy

Array manipulation mini-language. It can run up to one hundred times faster than the equivalent Python code. An even faster alternative that runs on a GPU is called CuPy.

# $ pip3 install numpy
+import numpy as np
+
+ + +
<array> = np.array(<list/list_of_lists>)
+<array> = np.arange(from_inclusive, to_exclusive, ±step_size)
+<array> = np.ones(<shape>)
+<array> = np.random.randint(from_inclusive, to_exclusive, <shape>)
+
+
<array>.shape = <shape>
+<view>  = <array>.reshape(<shape>)
+<view>  = np.broadcast_to(<array>, <shape>)
+
+
<array> = <array>.sum(axis)
+indexes = <array>.argmin(axis)
+
+ +

Indexing

<el>       = <2d_array>[row_index, column_index]
+<1d_view>  = <2d_array>[row_index]
+<1d_view>  = <2d_array>[:, column_index]
+
+ +
<1d_array> = <2d_array>[row_indexes, column_indexes]
+<2d_array> = <2d_array>[row_indexes]
+<2d_array> = <2d_array>[:, column_indexes]
+
+
<2d_bools> = <2d_array> ><== <el>
+<1d_array> = <2d_array>[<2d_bools>]
+
+

Broadcasting

Broadcasting is a set of rules by which NumPy functions operate on arrays of different sizes and/or dimensions.

left  = [[0.1], [0.6], [0.8]]        # Shape: (3, 1)
+right = [ 0.1 ,  0.6 ,  0.8 ]        # Shape: (3)
+
+ + +

1. If array shapes differ in length, left-pad the shorter shape with ones:

left  = [[0.1], [0.6], [0.8]]        # Shape: (3, 1)
+right = [[0.1 ,  0.6 ,  0.8]]        # Shape: (1, 3) <- !
+
+ +

2. If any dimensions differ in size, expand the ones that have size 1 by duplicating their elements:

left  = [[0.1, 0.1, 0.1], [0.6, 0.6, 0.6], [0.8, 0.8, 0.8]]  # Shape: (3, 3) <- !
+right = [[0.1, 0.6, 0.8], [0.1, 0.6, 0.8], [0.1, 0.6, 0.8]]  # Shape: (3, 3) <- !
+
+ +

3. If neither non-matching dimension has size 1, raise an error.

Example

For each point returns index of its nearest point ([0.1, 0.6, 0.8] => [1, 2, 1]):

>>> 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 = wrapped_points - 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. ]]
+>>> i = np.arange(3)
+[0, 1, 2]
+>>> distances[i, i] = np.inf
+[[ inf,  0.5,  0.7],
+ [ 0.5,  inf,  0.2],
+ [ 0.7,  0.2,  inf]]
+>>> distances.argmin(1)
+[1, 2, 1]
+
+ + + +

#Image

# $ pip3 install pillow
+from PIL import Image
+
+ +
<Image> = Image.new('<mode>', (width, height))  # Also: `color=<int/tuple/str>`.
+<Image> = Image.open(<path>)                    # Identifies format based on file contents.
+<Image> = <Image>.convert('<mode>')             # Converts image to the new mode.
+<Image>.save(<path>)                            # Selects format based on the path extension.
+<Image>.show()                                  # Opens image in default preview app.
+
+
<int/tuple> = <Image>.getpixel((x, y))          # Returns a pixel.
+<Image>.putpixel((x, y), <int/tuple>)           # Writes a pixel to the image.
+<ImagingCore> = <Image>.getdata()               # Returns a flattened sequence of pixels.
+<Image>.putdata(<list/ImagingCore>)             # Writes a flattened sequence of pixels.
+<Image>.paste(<Image>, (x, y))                  # Writes an image to the image.
+
+
<2d_array> = np.array(<Image_L>)                # Creates NumPy array from greyscale image.
+<3d_array> = np.array(<Image_RGB>)              # Creates NumPy array from color image.
+<Image>    = Image.fromarray(<array>)           # Creates image from NumPy array of floats.
+
+

Modes

Examples

Creates a PNG image of a rainbow gradient:

WIDTH, HEIGHT = 100, 100
+n_pixels = WIDTH * HEIGHT
+hues = (255 * i/n_pixels for i in range(n_pixels))
+img = Image.new('HSV', (WIDTH, HEIGHT))
+img.putdata([(int(h), 255, 255) for h in hues])
+img.convert('RGB').save('test.png')
+
+ + + + +

Adds noise to a PNG image:

from random import randint
+add_noise = lambda value: max(0, min(255, value + randint(-20, 20)))
+img = Image.open('test.png').convert('HSV')
+img.putdata([(add_noise(h), s, v) for h, s, v in img.getdata()])
+img.convert('RGB').save('test.png')
+
+ +

Image Draw

from PIL import ImageDraw
+<ImageDraw> = ImageDraw.Draw(<Image>)
+
+ +
<ImageDraw>.point((x, y))
+<ImageDraw>.line((x1, y1, x2, y2 [, ...]))
+<ImageDraw>.arc((x1, y1, x2, y2), from_deg, to_deg)
+<ImageDraw>.rectangle((x1, y1, x2, y2))
+<ImageDraw>.polygon((x1, y1, x2, y2 [, ...]))
+<ImageDraw>.ellipse((x1, y1, x2, y2))
+
+ +

#Animation

Creates a GIF of a bouncing ball:

# $ pip3 install imageio
+from PIL import Image, ImageDraw
+import imageio
+WIDTH, HEIGHT, R = 126, 126, 10
+frames = []
+for velocity in range(1, 16):
+    y = sum(range(velocity))
+    frame = Image.new('L', (WIDTH, HEIGHT))
+    draw  = ImageDraw.Draw(frame)
+    draw.ellipse((WIDTH/2-R, y, WIDTH/2+R, y+R*2), fill='white')
+    frames.append(frame)
+frames += reversed(frames[1:-1])
+imageio.mimsave('test.gif', frames, duration=0.03)
+
+ + +

#Audio

import wave
+
+ +
<Wave_read>  = wave.open('<path>', 'rb')        # Opens the WAV file.
+framerate    = <Wave_read>.getframerate()       # Number of frames per second.
+nchannels    = <Wave_read>.getnchannels()       # Number of samples per frame.
+sampwidth    = <Wave_read>.getsampwidth()       # Sample size in bytes.
+nframes      = <Wave_read>.getnframes()         # Number of frames.
+<params>     = <Wave_read>.getparams()          # Immutable collection of above.
+<bytes>      = <Wave_read>.readframes(nframes)  # Returns next 'nframes' frames.
+
+
<Wave_write> = wave.open('<path>', 'wb')        # Truncates existing file.
+<Wave_write>.setframerate(<int>)                # 44100 for CD, 48000 for video.
+<Wave_write>.setnchannels(<int>)                # 1 for mono, 2 for stereo.
+<Wave_write>.setsampwidth(<int>)                # 2 for CD quality sound.
+<Wave_write>.setparams(<params>)                # Sets all parameters.
+<Wave_write>.writeframes(<bytes>)               # Appends frames to the file.
+
+ +

Sample Values

┏━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━┯━━━━━━━━━━━━━┓
+┃ sampwidth │     min     │ zero │     max     ┃
+┠───────────┼─────────────┼──────┼─────────────┨
+┃     1     │           0 │  128 │         255 ┃
+┃     2     │      -32768 │    0 │       32767 ┃
+┃     3     │    -8388608 │    0 │     8388607 ┃
+┃     4     │ -2147483648 │    0 │  2147483647 ┃
+┗━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━┷━━━━━━━━━━━━━┛
+
+ +

Read Float Samples from WAV File

def read_wav_file(filename):
+    def get_int(bytes_obj):
+        an_int = int.from_bytes(bytes_obj, 'little', signed=(sampwidth != 1))
+        return an_int - 128 * (sampwidth == 1)
+    with wave.open(filename, 'rb') as file:
+        sampwidth = file.getsampwidth()
+        frames = file.readframes(-1)
+    bytes_samples = (frames[i : i+sampwidth] for i in range(0, len(frames), sampwidth))
+    return [get_int(b) / pow(2, sampwidth * 8 - 1) for b in bytes_samples]
+
+ +

Write Float Samples to WAV File

def write_to_wav_file(filename, float_samples, nchannels=1, sampwidth=2, framerate=44100):
+    def get_bytes(a_float):
+        a_float = max(-1, min(1 - 2e-16, a_float))
+        a_float += sampwidth == 1
+        a_float *= pow(2, sampwidth * 8 - 1)
+        return int(a_float).to_bytes(sampwidth, 'little', signed=(sampwidth != 1))
+    with wave.open(filename, 'wb') as file:
+        file.setnchannels(nchannels)
+        file.setsampwidth(sampwidth)
+        file.setframerate(framerate)
+        file.writeframes(b''.join(get_bytes(f) for f in float_samples))
+
+ +

Examples

Saves a 440 Hz sine wave to a mono WAV file:

from math import pi, sin
+samples_f = (sin(i * 2 * pi * 440 / 44100) for i in range(100000))
+write_to_wav_file('test.wav', samples_f)
+
+ + +

Adds noise to a mono WAV file:

from random import random
+add_noise = lambda value: value + (random() - 0.5) * 0.03
+samples_f = (add_noise(f) for f in read_wav_file('test.wav'))
+write_to_wav_file('test.wav', samples_f)
+
+ +

Plays a WAV file:

# $ pip3 install simpleaudio
+from simpleaudio import play_buffer
+with wave.open('test.wav', 'rb') as file:
+    p = file.getparams()
+    frames = file.readframes(-1)
+    play_buffer(frames, p.nchannels, p.sampwidth, p.framerate)
+
+ +

Text to Speech

# $ pip3 install pyttsx3
+import pyttsx3
+engine = pyttsx3.init()
+engine.say('Sally sells seashells by the seashore.')
+engine.runAndWait()
+
+ +

#Synthesizer

Plays Popcorn by Gershon Kingsley:

# $ pip3 install simpleaudio
+import math, struct, simpleaudio
+from itertools import repeat, chain
+F  = 44100
+P1 = '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: 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 key: 8.176 * 2 ** (int(key) / 12)
+parse_note  = lambda note: (get_hz(note[:2]), 1/4 if '♩' in note else 1/8)
+get_samples = lambda note: get_wave(*parse_note(note)) if note else get_pause(1/8)
+samples_f   = chain.from_iterable(get_samples(n) for n in f'{P1},{P1},{P2}'.split(','))
+samples_b   = b''.join(struct.pack('<h', int(f * 30000)) for f in samples_f)
+simpleaudio.play_buffer(samples_b, 1, 2, F)
+
+ + +

#Pygame

Basic Example

# $ pip3 install pygame
+import pygame as pg
+pg.init()
+screen = pg.display.set_mode((500, 500))
+rect = pg.Rect(240, 240, 20, 20)
+while all(event.type != pg.QUIT for event in pg.event.get()):
+    deltas = {pg.K_UP: (0, -1), pg.K_RIGHT: (1, 0), pg.K_DOWN: (0, 1), pg.K_LEFT: (-1, 0)}
+    for ch, is_pressed in enumerate(pg.key.get_pressed()):
+        rect = rect.move(deltas[ch]) if ch in deltas and is_pressed else rect
+    screen.fill((0, 0, 0))
+    pg.draw.rect(screen, (255, 255, 255), rect)
+    pg.display.flip()
+
+ + +

Rectangle

Object for storing rectangular coordinates.

<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((x, y))                    # Use move_ip() to move in-place.
+
+ + +
<bool> = <Rect>.collidepoint((x, y))            # Checks if rectangle contains a point.
+<bool> = <Rect>.colliderect(<Rect>)             # Checks if two rectangles overlap.
+<int>  = <Rect>.collidelist(<list_of_Rect>)     # Returns index of first colliding Rect or -1.
+<list> = <Rect>.collidelistall(<list_of_Rect>)  # Returns indexes of all colliding rectangles.
+
+

Surface

Object for representing images.

<Surf> = pg.display.set_mode((width, height))   # Returns a display surface.
+<Surf> = pg.Surface((width, height))            # New RGB surface. RGBA if `flags=pg.SRCALPHA`.
+<Surf> = pg.image.load('<path>')                # Loads the image. Format depends on source.
+<Surf> = <Surf>.subsurface(<Rect>)              # Returns a subsurface.
+
+ + +
<Surf>.fill(color)                              # Tuple, Color('#rrggbb[aa]') or Color(<name>).
+<Surf>.set_at((x, y), color)                    # Updates pixel.
+<Surf>.blit(<Surf>, (x, y))                     # Draws passed surface to the surface.
+
+
from pygame.transform import scale, ...
+<Surf> = scale(<Surf>, (width, height))         # Returns scaled surface.
+<Surf> = rotate(<Surf>, degrees)                # Returns rotated and scaled surface.
+<Surf> = flip(<Surf>, x_bool, y_bool)           # Returns flipped surface.
+
+
from pygame.draw import line, ...
+line(<Surf>, color, (x1, y1), (x2, y2), width)  # Draws a line to the surface.
+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

<Font> = pg.font.SysFont('<name>', size)        # Loads the system font or default if missing.
+<Font> = pg.font.Font('<path>', size)           # Loads the TTF file. Pass None for default.
+<Surf> = <Font>.render(text, antialias, color)  # Background color can be specified at the end.
+
+ +

Sound

<Sound> = pg.mixer.Sound('<path>')              # Loads the WAV file.
+<Sound>.play()                                  # Starts playing the sound.
+
+ +

Basic Mario Brothers Example

import collections, dataclasses, enum, io, itertools as it, pygame as pg, urllib.request
+from random import randint
+
+P = collections.namedtuple('P', 'x y')          # Position
+D = enum.Enum('D', 'n e s w')                   # Direction
+W, H, MAX_S = 50, 50, P(5, 10)                  # Width, Height, Max speed
+
+def main():
+    def get_screen():
+        pg.init()
+        return pg.display.set_mode((W*16, H*16))
+    def get_images():
+        url = 'https://gto76.github.io/python-cheatsheet/web/mario_bros.png'
+        img = pg.image.load(io.BytesIO(urllib.request.urlopen(url).read()))
+        return [img.subsurface(get_rect(x, 0)) for x in range(img.get_width() // 16)]
+    def get_mario():
+        Mario = dataclasses.make_dataclass('Mario', 'rect spd facing_left frame_cycle'.split())
+        return Mario(get_rect(1, 1), P(0, 0), False, it.cycle(range(3)))
+    def get_tiles():
+        border = [(x, y) for x in range(W) for y in range(H) if x in [0, W-1] or y in [0, H-1]]
+        platforms = [(randint(1, W-2), randint(2, H-2)) for _ in range(W*H // 10)]
+        return [get_rect(x, y) for x, y in border + platforms]
+    def get_rect(x, y):
+        return pg.Rect(x*16, y*16, 16, 16)
+    run(get_screen(), get_images(), get_mario(), get_tiles())
+
+def run(screen, images, mario, tiles):
+    clock = pg.time.Clock()
+    while all(event.type != pg.QUIT for event in pg.event.get()):
+        keys = {pg.K_UP: D.n, pg.K_RIGHT: D.e, pg.K_DOWN: D.s, pg.K_LEFT: D.w}
+        pressed = {keys.get(ch) for ch, is_prsd in enumerate(pg.key.get_pressed()) if is_prsd}
+        update_speed(mario, tiles, pressed)
+        update_position(mario, tiles)
+        draw(screen, images, mario, tiles, pressed)
+        clock.tick(28)
+
+def update_speed(mario, tiles, pressed):
+    x, y = mario.spd
+    x += 2 * ((D.e in pressed) - (D.w 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
+    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):
+    x, y = mario.rect.topleft
+    n_steps = max(abs(s) for s in mario.spd)
+    for _ in range(n_steps):
+        mario.spd = stop_on_collision(mario.spd, get_boundaries(mario.rect, tiles))
+        x, y = x + mario.spd.x / n_steps, y + mario.spd.y / n_steps
+        mario.rect.topleft = x, y
+
+def get_boundaries(rect, tiles):
+    deltas = {D.n: P(0, -1), D.e: P(1, 0), D.s: P(0, 1), D.w: P(-1, 0)}
+    return {d for d, delta in deltas.items() if rect.move(delta).collidelist(tiles) != -1}
+
+def stop_on_collision(spd, bounds):
+    return P(x=0 if (D.w in bounds and spd.x < 0) or (D.e in bounds and spd.x > 0) else spd.x,
+             y=0 if (D.n in bounds and spd.y < 0) or (D.s in bounds and spd.y > 0) else spd.y)
+
+def draw(screen, images, mario, tiles, pressed):
+    def get_marios_image_index():
+        if D.s not in get_boundaries(mario.rect, tiles):
+            return 4
+        return next(mario.frame_cycle) if {D.w, D.e} & pressed else 6
+    screen.fill((85, 168, 255))
+    mario.facing_left = (D.w in pressed) if {D.w, D.e} & pressed else mario.facing_left
+    screen.blit(images[get_marios_image_index() + mario.facing_left * 9], mario.rect)
+    for t in tiles:
+        screen.blit(images[18 if t.x in [0, (W-1)*16] or t.y in [0, (H-1)*16] else 19], t)
+    pg.display.flip()
+
+if __name__ == '__main__':
+    main()
+
+ +

#Pandas

# $ pip3 install pandas
+import pandas as pd
+from pandas import Series, DataFrame
+
+ +

Series

Ordered dictionary with a name.

>>> Series([1, 2], index=['x', 'y'], name='a')
+x    1
+y    2
+Name: a, dtype: int64
+
+ + +
<Sr> = Series(<list>)                         # Assigns RangeIndex starting at 0.
+<Sr> = Series(<dict>)                         # Takes dictionary's keys for index.
+<Sr> = Series(<dict/Series>, index=<list>)    # Only keeps items with keys specified in index.
+
+
<el> = <Sr>.loc[key]                          # Or: <Sr>.iloc[index]
+<Sr> = <Sr>.loc[keys]                         # Or: <Sr>.iloc[indexes]
+<Sr> = <Sr>.loc[from_key : to_key_inclusive]  # Or: <Sr>.iloc[from_i : to_i_exclusive]
+
+
<el> = <Sr>[key/index]                        # Or: <Sr>.key
+<Sr> = <Sr>[keys/indexes]                     # Or: <Sr>[<key_range/range>]
+<Sr> = <Sr>[bools]                            # Or: <Sr>.i/loc[bools]
+
+
<Sr> = <Sr> ><== <el/Sr>                      # Returns a Series of bools.
+<Sr> = <Sr> +-*/ <el/Sr>                      # Items with non-matching keys get value NaN.
+
+
<Sr> = <Sr>.append(<Sr>)                      # Or: pd.concat(<coll_of_Sr>)
+<Sr> = <Sr>.combine_first(<Sr>)               # Adds items that are not yet present.
+<Sr>.update(<Sr>)                             # Updates items that are already present.
+
+
<Sr>.plot.line/area/bar/pie/hist()            # Generates a Matplotlib plot.
+matplotlib.pyplot.show()                      # Displays the plot. Also savefig(<path>).
+
+

Series — Aggregate, Transform, Map:

<el> = <Sr>.sum/max/mean/idxmax/all()         # Or: <Sr>.agg(lambda <Sr>: <el>)
+<Sr> = <Sr>.rank/diff/cumsum/ffill/interpl()  # Or: <Sr>.agg/transform(lambda <Sr>: <Sr>)
+<Sr> = <Sr>.fillna(<el>)                      # Or: <Sr>.agg/transform/map(lambda <el>: <el>)
+
+ +
>>> sr = Series([1, 2], index=['x', 'y'])
+x    1
+y    2
+
+
┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
+┃                 │    'sum'    │   ['sum']   │ {'s': 'sum'}  ┃
+┠─────────────────┼─────────────┼─────────────┼───────────────┨
+┃ sr.apply(…)     │      3      │    sum  3   │     s  3      ┃
+┃ sr.agg(…)       │             │             │               ┃
+┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
+
+┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
+┃                 │    'rank'   │   ['rank']  │ {'r': 'rank'} ┃
+┠─────────────────┼─────────────┼─────────────┼───────────────┨
+┃ sr.apply(…)     │             │      rank   │               ┃
+┃ sr.agg(…)       │     x  1    │   x     1   │    r  x  1    ┃
+┃ sr.transform(…) │     y  2    │   y     2   │       y  2    ┃
+┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
+
+ + +

DataFrame

Table with labeled rows and columns.

>>> DataFrame([[1, 2], [3, 4]], index=['a', 'b'], columns=['x', 'y'])
+   x  y
+a  1  2
+b  3  4
+
+ + +
<DF>    = DataFrame(<list_of_rows>)           # Rows can be either lists, dicts or series.
+<DF>    = DataFrame(<dict_of_columns>)        # Columns can be either lists, dicts or series.
+
+
<el>    = <DF>.loc[row_key, column_key]       # Or: <DF>.iloc[row_index, column_index]
+<Sr/DF> = <DF>.loc[row_key/s]                 # Or: <DF>.iloc[row_index/es]
+<Sr/DF> = <DF>.loc[:, column_key/s]           # Or: <DF>.iloc[:, column_index/es]
+<DF>    = <DF>.loc[row_bools, column_bools]   # Or: <DF>.iloc[row_bools, column_bools]
+
+
<Sr/DF> = <DF>[column_key/s]                  # Or: <DF>.column_key
+<DF>    = <DF>[row_bools]                     # Keeps rows as specified by bools.
+<DF>    = <DF>[<DF_of_bools>]                 # Assigns NaN to False values.
+
+
<DF>    = <DF> ><== <el/Sr/DF>                # Returns DF of bools. Sr is treated as a row.
+<DF>    = <DF> +-*/ <el/Sr/DF>                # Items with non-matching keys get value NaN.
+
+
<DF>    = <DF>.set_index(column_key)          # Replaces row keys with values from a column.
+<DF>    = <DF>.reset_index()                  # Moves row keys to a column named index.
+<DF>    = <DF>.sort_index(ascending=True)     # Sorts rows by row keys.
+<DF>    = <DF>.sort_values(column_key/s)      # Sorts rows by the passed column/s.
+
+

DataFrame — Merge, Join, Concat:

>>> l = DataFrame([[1, 2], [3, 4]], index=['a', 'b'], columns=['x', 'y'])
+   x  y
+a  1  2
+b  3  4
+>>> r = DataFrame([[4, 5], [6, 7]], index=['b', 'c'], columns=['y', 'z'])
+   y  z
+b  4  5
+c  6  7
+
+ +
┏━━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+┃                        │    'outer'    │   'inner'  │   'left'   │       Description        ┃
+┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
+┃ l.merge(r, on='y',     │    x   y   z  │ x   y   z  │ x   y   z  │ Joins/merges on column.  ┃
+┃            how=…)      │ 0  1   2   .  │ 3   4   5  │ 1   2   .  │ Also accepts left_on and ┃
+┃                        │ 1  3   4   5  │            │ 3   4   5  │ right_on parameters.     ┃
+┃                        │ 2  .   6   7  │            │            │ Uses 'inner' by default. ┃
+┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
+┃ l.join(r, lsuffix='l', │    x yl yr  z │            │ x yl yr  z │ Joins/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. Use l.append(sr) ┃
+┃                        │ c  .   6   7  │     6      │            │ to add a row instead.    ┃
+┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
+┃ 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.     ┃
+┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
+┃ l.combine_first(r)     │    x   y   z  │            │            │ Adds missing rows and    ┃
+┃                        │ a  1   2   .  │            │            │ columns. Also updates    ┃
+┃                        │ b  3   4   5  │            │            │ items that contain NaN.  ┃
+┃                        │ c  .   6   7  │            │            │ R must be a DataFrame.   ┃
+┗━━━━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+

DataFrame — Aggregate, Transform, Map:

<Sr> = <DF>.sum/max/mean/idxmax/all()         # Or: <DF>.apply/agg(lambda <Sr>: <el>)
+<DF> = <DF>.rank/diff/cumsum/ffill/interpl()  # Or: <DF>.apply/agg/transform(lambda <Sr>: <Sr>)
+<DF> = <DF>.fillna(<el>)                      # Or: <DF>.applymap(lambda <el>: <el>)
+
+ + +
>>> df = DataFrame([[1, 2], [3, 4]], index=['a', 'b'], columns=['x', 'y'])
+   x  y
+a  1  2
+b  3  4
+
+
┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
+┃                 │    'sum'    │   ['sum']   │ {'x': 'sum'}  ┃
+┠─────────────────┼─────────────┼─────────────┼───────────────┨
+┃ df.apply(…)     │             │       x  y  │               ┃
+┃ df.agg(…)       │     x  4    │  sum  4  6  │     x  4      ┃
+┃                 │     y  6    │             │               ┃
+┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
+
+┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
+┃                 │    'rank'   │   ['rank']  │ {'x': 'rank'} ┃
+┠─────────────────┼─────────────┼─────────────┼───────────────┨
+┃ df.apply(…)     │      x  y   │      x    y │        x      ┃
+┃ df.agg(…)       │   a  1  1   │   rank rank │     a  1      ┃
+┃ df.transform(…) │   b  2  2   │ a    1    1 │     b  2      ┃
+┃                 │             │ b    2    2 │               ┃
+┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
+
+ + +

DataFrame — Plot, Encode, Decode:

import matplotlib.pyplot as plt
+<DF>.plot.line/bar/hist/scatter([x=column_key, y=column_key/s]); plt.show()
+
+ +
<DF> = pd.read_json/html('<str/path/url>')
+<DF> = pd.read_csv/pickle/excel('<path/url>')
+<DF> = pd.read_sql('<table_name/query>', <connection>)
+<DF> = pd.read_clipboard()
+
+
<dict> = <DF>.to_dict(['d/l/s/sp/r/i'])
+<str>  = <DF>.to_json/html/csv/markdown/latex([<path>])
+<DF>.to_pickle/excel(<path>)
+<DF>.to_sql('<table_name>', <connection>)
+
+

GroupBy

Object that groups together rows of a dataframe based on the value of the passed column.

>>> df = DataFrame([[1, 2, 3], [4, 5, 6], [7, 8, 6]], index=list('abc'), columns=list('xyz'))
+>>> df.groupby('z').get_group(6)
+   x  y
+b  4  5
+c  7  8
+
+ + +
<GB> = <DF>.groupby(column_key/s)             # DF is split into groups based on passed column.
+<DF> = <GB>.apply(<func>)                     # Maps each group. Func can return DF, Sr or el.
+<GB> = <GB>[column_key]                       # A single column GB. All operations return a Sr.
+
+

GroupBy — Aggregate, Transform, Map:

<DF> = <GB>.sum/max/mean/idxmax/all()         # Or: <GB>.agg(lambda <Sr>: <el>)
+<DF> = <GB>.rank/diff/cumsum/ffill()          # Or: <GB>.transform(lambda <Sr>: <Sr>)
+<DF> = <GB>.fillna(<el>)                      # Or: <GB>.transform(lambda <Sr>: <Sr>)
+
+ +
>>> gb = df.groupby('z')
+      x  y  z
+3: a  1  2  3
+6: b  4  5  6
+   c  7  8  6
+
+
┏━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
+┃                 │    'sum'    │    'rank'   │   ['rank']  │ {'x': 'rank'} ┃
+┠─────────────────┼─────────────┼─────────────┼─────────────┼───────────────┨
+┃ gb.agg(…)       │      x   y  │      x  y   │      x    y │        x      ┃
+┃                 │  z          │   a  1  1   │   rank rank │     a  1      ┃
+┃                 │  3   1   2  │   b  1  1   │ a    1    1 │     b  1      ┃
+┃                 │  6  11  13  │   c  2  2   │ b    1    1 │     c  2      ┃
+┃                 │             │             │ c    2    2 │               ┃
+┠─────────────────┼─────────────┼─────────────┼─────────────┼───────────────┨
+┃ gb.transform(…) │      x   y  │      x  y   │             │               ┃
+┃                 │  a   1   2  │   a  1  1   │             │               ┃
+┃                 │  b  11  13  │   b  1  1   │             │               ┃
+┃                 │  c  11  13  │   c  2  2   │             │               ┃
+┗━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
+
+

Rolling

Object for rolling window calculations.

<R_Sr/R_DF/R_GB> = <Sr/DF/GB>.rolling(window_size)  # Also: `min_periods=None, center=False`.
+<R_Sr/R_DF>      = <R_DF/R_GB>[column_key/s]        # Or: <R>.column_key
+<Sr/DF/DF>       = <R_Sr/R_DF/R_GB>.sum/max/mean()  # Or: <R>.apply/agg(<agg_func/str>)
+
+ + +

#Plotly

# $ pip3 install plotly kaleido
+from plotly.express import line
+<Figure> = line(<DF>, x=<col_name>, y=<col_name>)        # Or: line(x=<list>, y=<list>)
+<Figure>.update_layout(margin=dict(t=0, r=0, b=0, l=0))  # Or: paper_bgcolor='rgba(0, 0, 0, 0)'
+<Figure>.write_html/json/image('<path>')                 # Also: <Figure>.show()
+
+ +

Covid deaths by continent:

covid = pd.read_csv('https://covid.ourworldindata.org/data/owid-covid-data.csv',
+                    usecols=['iso_code', 'date', 'total_deaths', 'population'])
+continents = pd.read_csv('https://gist.githubusercontent.com/stevewithington/20a69c0b6d2ff'
+                         '846ea5d35e5fc47f26c/raw/country-and-continent-codes-list-csv.csv',
+                         usecols=['Three_Letter_Country_Code', 'Continent_Name'])
+df = pd.merge(covid, continents, left_on='iso_code', right_on='Three_Letter_Country_Code')
+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')
+line(df, x='Date', y='Total Deaths per Million', color='Continent').show()
+
+ + + +

Confirmed covid cases, Dow Jones, Gold, and Bitcoin price:

import pandas as pd
+import plotly.graph_objects as go
+
+def main():
+    display_data(wrangle_data(*scrape_data()))
+
+def scrape_data():
+    def scrape_covid():
+        url = 'https://covid.ourworldindata.org/data/owid-covid-data.csv'
+        df = pd.read_csv(url, usecols=['location', 'date', 'total_cases'])
+        return df[df.location == 'World'].set_index('date').total_cases
+    def scrape_yahoo(slug):
+        url = f'https://query1.finance.yahoo.com/v7/finance/download/%3Cspan%20class="hljs-subst">{slug}' + \
+              '?period1=1579651200&period2=9999999999&interval=1d&events=history'
+        df = pd.read_csv(url, usecols=['Date', 'Close'])
+        return df.set_index('Date').Close
+    out = scrape_covid(), scrape_yahoo('BTC-USD'), scrape_yahoo('GC=F'), scrape_yahoo('^DJI')
+    return map(pd.Series.rename, out, ['Total Cases', 'Bitcoin', 'Gold', 'Dow Jones'])
+
+def wrangle_data(covid, bitcoin, gold, dow):
+    df = pd.concat([bitcoin, gold, dow], axis=1)  # Joins columns on dates.
+    df = df.sort_index().interpolate()            # Sorts by date and interpolates NaN-s.
+    df = df.loc['2020-02-23':]                    # Discards rows before '2020-02-23'.
+    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.
+
+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)
+        figure.add_trace(trace)
+    figure.update_layout(
+        yaxis1=dict(title='Total Cases', rangemode='tozero'),
+        yaxis2=dict(title='%', rangemode='tozero', overlaying='y', side='right'),
+        legend=dict(x=1.1),
+        height=450
+    ).show()
+
+if __name__ == '__main__':
+    main()
+
+ + + +

#PySimpleGUI

# $ pip3 install PySimpleGUI
+import PySimpleGUI as sg
+layout = [[sg.Text("What's your name?")], [sg.Input()], [sg.Button('Ok')]]
+window = sg.Window('Window Title', layout)
+event, values = window.read()
+print(f'Hello {values[0]}!' if event == 'Ok' else '')
+
+ +

#Appendix

Cython

Library that compiles Python code into C.

# $ pip3 install cython
+import pyximport; pyximport.install()
+import <cython_script>
+<cython_script>.main()
+
+ + + +

Definitions:

cdef <ctype> <var_name> = <el>
+cdef <ctype>[n_elements] <var_name> = [<el_1>, <el_2>, ...]
+cdef <ctype/void> <func_name>(<ctype> <arg_name>): ...
+
+ + +
cdef class <class_name>:
+    cdef public <ctype> <attr_name>
+    def __init__(self, <ctype> <arg_name>):
+        self.<attr_name> = <arg_name>
+
+
cdef enum <enum_name>: <member_name_1>, <member_name_2>, ...
+
+

PyInstaller

$ pip3 install pyinstaller
+$ pyinstaller script.py                        # Compiles into './dist/script' directory.
+$ pyinstaller script.py --onefile              # Compiles into './dist/script' console app.
+$ pyinstaller script.py --windowed             # Compiles into './dist/script' windowed app.
+$ pyinstaller script.py --add-data '<path>:.'  # Adds file to the root of the executable.
+
+ + +

Basic Script Template

#!/usr/bin/env python3
+#
+# Usage: .py
+#
+
+from sys import argv, exit
+from collections import defaultdict, namedtuple
+from dataclasses import make_dataclass
+from enum import Enum
+import functools as ft, itertools as it, operator as op, re
+
+
+def main():
+    pass
+
+
+###
+##  UTIL
+#
+
+def read_file(filename):
+    with open(filename, encoding='utf-8') as file:
+        return file.readlines()
+
+
+if __name__ == '__main__':
+    main()
+
+ +

#Index

+ + + + + + + + + + + + + + +