-
Notifications
You must be signed in to change notification settings - Fork 6.6k
/
Copy pathindex.html
2957 lines (2535 loc) · 318 KB
/
index.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE html>
<html class="ocks-org do-not-copy" lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, minimum-scale=1" />
<title>Comprehensive Python Cheatsheet</title>
<meta name="description" content="Exhaustive, simple, beautiful and concise. A truly Pythonic cheat sheet about Python programming language.">
<link rel="icon" href="web/favicon.png">
<link rel="stylesheet" href="web/default.min.css">
<link rel="stylesheet" href="https://netdna.bootstrapcdn.com/font-awesome/3.2.1/css/font-awesome.css">
<link rel="stylesheet" href="web/style.css">
<script>
// Uses dark theme 3 if it's specified in query string orbrowser prefers dark mode and
// theme is not explicitly set.
if ((window.location.search.search(/[?&]theme=dark3/) !== -1) || ((window.location.search.search(/[?&]theme=/) == -1) && (window.matchMedia('(prefers-color-scheme: dark)').matches))) {
document.write("<link rel=\"stylesheet\" href=\"web/default_dark3.min.css\">");
document.write("<link rel=\"stylesheet\" href=\"web/style_dark3.css\">");
}
else if (window.location.search.search(/[?&]theme=dark2/) !== -1) {
document.write("<link rel=\"stylesheet\" href=\"web/default_dark2.min.css\">");
document.write("<link rel=\"stylesheet\" href=\"web/style_dark2.css\">");
}
else if (window.location.search.search(/[?&]theme=dark1/) !== -1) {
document.write("<link rel=\"stylesheet\" href=\"web/default_dark1.min.css\">");
document.write("<link rel=\"stylesheet\" href=\"web/style_dark1.css\">");
}
else if (window.location.search.search(/[?&]theme=dark/) !== -1) {
document.write("<link rel=\"stylesheet\" href=\"web/default_dark.min.css\">");
document.write("<link rel=\"stylesheet\" href=\"web/style_dark.css\">");
}
</script>
<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:title" content="Comprehensive Python Cheatsheet">
<meta name="twitter:description" content="Exhaustive, simple, beautiful and concise. A truly Pythonic cheat sheet about Python programming language.">
<meta name="twitter:image" content="https://gto76.github.io/python-cheatsheet/web/image_social_4.png">
<meta property="og:url" content="https://gto76.github.io/python-cheatsheet/">
<meta property="og:title" content="Comprehensive Python Cheatsheet">
<meta property="og:description" content="Exhaustive, simple, beautiful and concise. A truly Pythonic cheat sheet about Python programming language.">
<meta property="og:site_name" content="gto76.github.io">
<meta property="og:image" content="https://gto76.github.io/python-cheatsheet/web/image_social_4.png">
<meta property="og:type" content="article">
<meta itemprop="url" content="https://gto76.github.io/python-cheatsheet/">
<meta itemprop="name" content="Comprehensive Python Cheatsheet">
<meta itemprop="description" content="Exhaustive, simple, beautiful and concise. A truly Pythonic cheat sheet about Python programming language.">
<meta itemprop="image" content="https://gto76.github.io/python-cheatsheet/web/image_social_4.png">
<meta name="google-site-verification" content="w3rvuG0D1kUm_w20qsJecSEZh59Am8jK4eSPVU83e_M">
<meta name="viewport" id="viewport-meta">
</head>
<body>
<header>
<aside>April 30, 2025</aside>
<a href="https://gto76.github.io" rel="author">Jure Šorn</a>
</header>
<div><h1 id="comprehensivepythoncheatsheet">Comprehensive Python Cheatsheet</h1><p class="banner"><sup><a href="https://raw.githubusercontent.com/gto76/python-cheatsheet/main/README.md">Download text file</a>, <a href="https://github.com/gto76/python-cheatsheet">Fork me on GitHub</a>, <a href="https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions">Check out FAQ</a> or <a href="index.html?theme=dark3">Switch to dark theme</a>.
</sup></p><p class="banner" style="margin-bottom: 20px; padding-bottom: 7px;"><img src="web/image_888.jpeg" alt="Monty Python"></p><script>
// Changes the banner image and link-to-theme if "theme=dark" is in query string
// or if browser prefers dark mode and theme is not explicitly set.
const theme_not_set_in_query = window.location.search.search(/[?&]theme=light/) == -1
const browser_prefers_dark = window.matchMedia('(prefers-color-scheme: dark)').matches;
if ((window.location.search.search(/[?&]theme=dark/) !== -1) ||
(theme_not_set_in_query && browser_prefers_dark)) {
activateDarkMode();
}
function activateDarkMode() {
var link_to_theme = document.createElement("a")
link_to_theme.href = "index.html?theme=light"
link_to_theme.text = "Switch to light theme"
document.getElementsByClassName("banner")[0].firstChild.children[3].replaceWith(link_to_theme)
var img_dark = document.createElement("img");
img_dark.src = "web/image_orig_blue6.png";
img_dark.alt = "Monthy Python";
if ((window.location.search.search(/[?&]theme=dark2/) !== -1) ||
(window.location.search.search(/[?&]theme=dark3/) !== -1) ||
(theme_not_set_in_query && browser_prefers_dark)) {
img_dark.style = "width: 910px;";
} else {
img_dark.style = "width: 960px;";
}
document.getElementsByClassName("banner")[1].firstChild.replaceWith(img_dark);
}
</script><pre style="border-left: none;padding-left: 1.9px;"><code class="hljs bash" style="line-height: 1.327em;"><strong>ToC</strong> = {
<strong><span class="hljs-string"><span class="hljs-string">'1. Collections'</span></span></strong>: [<a href="#list">List</a>, <a href="#dictionary">Dictionary</a>, <a href="#set">Set</a>, <a href="#tuple">Tuple</a>, <a href="#range">Range</a>, <a href="#enumerate">Enumerate</a>, <a href="#iterator">Iterator</a>, <a href="#generator">Generator</a>],
<strong><span class="hljs-string"><span class="hljs-string">'2. Types'</span></span></strong>: [<a href="#type">Type</a>, <a href="#string">String</a>, <a href="#regex">Regular_Exp</a>, <a href="#format">Format</a>, <a href="#numbers">Numbers</a>, <a href="#combinatorics">Combinatorics</a>, <a href="#datetime">Datetime</a>],
<strong><span class="hljs-string"><span class="hljs-string">'3. Syntax'</span></span></strong>: [<a href="#function">Function</a>, <a href="#inline">Inline</a>, <a href="#imports">Import</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#ducktypes">Duck_Type</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Except</a>],
<strong><span class="hljs-string"><span class="hljs-string">'4. System'</span></span></strong>: [<a href="#exit">Exit</a>, <a href="#print">Print</a>, <a href="#input">Input</a>, <a href="#commandlinearguments">Command_Line_Arguments</a>, <a href="#open">Open</a>, <a href="#paths">Path</a>, <a href="#oscommands">OS_Commands</a>],
<strong><span class="hljs-string"><span class="hljs-string">'5. Data'</span></span></strong>: [<a href="#json">JSON</a>, <a href="#pickle">Pickle</a>, <a href="#csv">CSV</a>, <a href="#sqlite">SQLite</a>, <a href="#bytes">Bytes</a>, <a href="#struct">Struct</a>, <a href="#array">Array</a>, <a href="#memoryview">Memory_View</a>, <a href="#deque">Deque</a>],
<strong><span class="hljs-string"><span class="hljs-string">'6. Advanced'</span></span></strong>: [<a href="#operator">Operator</a>, <a href="#matchstatement">Match_Stmt</a>, <a href="#logging">Logging</a>, <a href="#introspection">Introspection</a>, <a href="#threading">Threading</a>, <a href="#coroutines">Coroutines</a>],
<strong><span class="hljs-string"><span class="hljs-string">'7. Libraries'</span></span></strong>: [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#consoleapp">Console_App</a>, <a href="#guiapp">GUI</a>, <a href="#scraping">Scraping</a>, <a href="#webapp">Web</a>, <a href="#profiling">Profile</a>],
<strong><span class="hljs-string"><span class="hljs-string">'8. Multimedia'</span></span></strong>: [<a href="#numpy">NumPy</a>, <a href="#image">Image</a>, <a href="#animation">Animation</a>, <a href="#audio">Audio</a>, <a href="#synthesizer">Synthesizer</a>, <a href="#pygame">Pygame</a>, <a href="#pandas">Pandas</a>, <a href="#plotly">Plotly</a>]
}
</code></pre></div>
<div><h2 id="main"><a href="#main" name="main">#</a>Main</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>: <span class="hljs-comment"># Skips next line if file was imported.</span>
main() <span class="hljs-comment"># Runs `def main(): ...` function.</span>
</code></pre></div>
<div><h2 id="list"><a href="#list" name="list">#</a>List</h2><pre><code class="python language-python hljs"><list> = [<el_1>, <el_2>, ...] <span class="hljs-comment"># Creates new list. Also list(<collection>).</span>
</code></pre></div>
<pre><code class="python language-python hljs"><el> = <list>[index] <span class="hljs-comment"># First index is 0. Last -1. Allows assignments.</span>
<list> = <list>[<slice>] <span class="hljs-comment"># Also <list>[from_inclusive : to_exclusive : ±step].</span>
</code></pre>
<pre><code class="python language-python hljs"><list>.append(<el>) <span class="hljs-comment"># Appends element to the end. Also <list> += [<el>].</span>
<list>.extend(<collection>) <span class="hljs-comment"># Appends elements to the end. Also <list> += <coll>.</span>
</code></pre>
<pre><code class="python language-python hljs"><list>.sort() <span class="hljs-comment"># Sorts elements in ascending order.</span>
<list>.reverse() <span class="hljs-comment"># Reverses the list in-place.</span>
<list> = sorted(<collection>) <span class="hljs-comment"># Returns new list with sorted elements.</span>
<iter> = reversed(<list>) <span class="hljs-comment"># Returns reversed iterator of elements.</span>
</code></pre>
<pre><code class="python language-python hljs"><el> = max(<collection>) <span class="hljs-comment"># Returns largest element. Also min(<el_1>, ...).</span>
<num> = sum(<collection>) <span class="hljs-comment"># Returns sum of elements. Also math.prod(<coll>).</span>
</code></pre>
<pre><code class="python language-python hljs">elementwise_sum = [sum(pair) <span class="hljs-keyword">for</span> pair <span class="hljs-keyword">in</span> zip(list_a, list_b)]
sorted_by_second = sorted(<collection>, key=<span class="hljs-keyword">lambda</span> el: el[<span class="hljs-number">1</span>])
sorted_by_both = sorted(<collection>, key=<span class="hljs-keyword">lambda</span> el: (el[<span class="hljs-number">1</span>], el[<span class="hljs-number">0</span>]))
flatter_list = list(itertools.chain.from_iterable(<list>))
</code></pre>
<ul>
<li><strong>For details about sort(), sorted(), min() and max() see <a href="#sortable">Sortable</a>.</strong></li>
<li><strong>Module <a href="#operator">operator</a> has function itemgetter() that can replace listed <a href="#lambda">lambdas</a>.</strong></li>
<li><strong>This text uses the term collection instead of iterable. For rationale see <a href="#collection">Collection</a>.</strong></li>
</ul>
<pre><code class="python language-python hljs"><int> = len(<list>) <span class="hljs-comment"># Returns number of items. Also works on dict, set and string.</span>
<int> = <list>.count(<el>) <span class="hljs-comment"># Returns number of occurrences. Also `if <el> in <coll>: ...`.</span>
<int> = <list>.index(<el>) <span class="hljs-comment"># Returns index of the first occurrence or raises ValueError.</span>
<el> = <list>.pop() <span class="hljs-comment"># Removes and returns item from the end or at index if passed.</span>
<list>.insert(<int>, <el>) <span class="hljs-comment"># Inserts item at index and moves the rest to the right.</span>
<list>.remove(<el>) <span class="hljs-comment"># Removes first occurrence of the item or raises ValueError.</span>
<list>.clear() <span class="hljs-comment"># Removes all items. Also works on dictionary and set.</span>
</code></pre>
<div><h2 id="dictionary"><a href="#dictionary" name="dictionary">#</a>Dictionary</h2><pre><code class="python language-python hljs"><dict> = {key_1: val_1, key_2: val_2, ...} <span class="hljs-comment"># Use `<dict>[key]` to get or set the value.</span>
</code></pre></div>
<pre><code class="python language-python hljs"><view> = <dict>.keys() <span class="hljs-comment"># Collection of keys that reflects changes.</span>
<view> = <dict>.values() <span class="hljs-comment"># Collection of values that reflects changes.</span>
<view> = <dict>.items() <span class="hljs-comment"># Coll. of key-value tuples that reflects chgs.</span>
</code></pre>
<pre><code class="python language-python hljs">value = <dict>.get(key, default=<span class="hljs-keyword">None</span>) <span class="hljs-comment"># Returns default if key is missing.</span>
value = <dict>.setdefault(key, default=<span class="hljs-keyword">None</span>) <span class="hljs-comment"># Returns and writes default if key is missing.</span>
<dict> = collections.defaultdict(<type>) <span class="hljs-comment"># Returns a dict with default value `<type>()`.</span>
<dict> = collections.defaultdict(<span class="hljs-keyword">lambda</span>: <span class="hljs-number">1</span>) <span class="hljs-comment"># Returns a dict with default value 1.</span>
</code></pre>
<pre><code class="python language-python hljs"><dict> = dict(<collection>) <span class="hljs-comment"># Creates a dict from coll. of key-value pairs.</span>
<dict> = dict(zip(keys, values)) <span class="hljs-comment"># Creates a dict from two collections.</span>
<dict> = dict.fromkeys(keys [, value]) <span class="hljs-comment"># Creates a dict from collection of keys.</span>
</code></pre>
<pre><code class="python language-python hljs"><dict>.update(<dict>) <span class="hljs-comment"># Adds items. Replaces ones with matching keys.</span>
value = <dict>.pop(key) <span class="hljs-comment"># Removes item or raises KeyError if missing.</span>
{k <span class="hljs-keyword">for</span> k, v <span class="hljs-keyword">in</span> <dict>.items() <span class="hljs-keyword">if</span> v == value} <span class="hljs-comment"># Returns set of keys that point to the value.</span>
{k: v <span class="hljs-keyword">for</span> k, v <span class="hljs-keyword">in</span> <dict>.items() <span class="hljs-keyword">if</span> k <span class="hljs-keyword">in</span> keys} <span class="hljs-comment"># Filters the dictionary by keys.</span>
</code></pre>
<div><h3 id="counter">Counter</h3><pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> Counter
<span class="hljs-meta">>>> </span>counter = Counter([<span class="hljs-string">'blue'</span>, <span class="hljs-string">'blue'</span>, <span class="hljs-string">'blue'</span>, <span class="hljs-string">'red'</span>, <span class="hljs-string">'red'</span>])
<span class="hljs-meta">>>> </span>counter[<span class="hljs-string">'yellow'</span>] += <span class="hljs-number">1</span>
<span class="hljs-meta">>>> </span>print(counter.most_common())
[(<span class="hljs-string">'blue'</span>, <span class="hljs-number">3</span>), (<span class="hljs-string">'red'</span>, <span class="hljs-number">2</span>), (<span class="hljs-string">'yellow'</span>, <span class="hljs-number">1</span>)]
</code></pre></div>
<div><h2 id="set"><a href="#set" name="set">#</a>Set</h2><pre><code class="python language-python hljs"><set> = {<el_1>, <el_2>, ...} <span class="hljs-comment"># Use `set()` for empty set.</span>
</code></pre></div>
<pre><code class="python language-python hljs"><set>.add(<el>) <span class="hljs-comment"># Or: <set> |= {<el>}</span>
<set>.update(<collection> [, ...]) <span class="hljs-comment"># Or: <set> |= <set></span>
</code></pre>
<pre><code class="python language-python hljs"><set> = <set>.union(<coll.>) <span class="hljs-comment"># Or: <set> | <set></span>
<set> = <set>.intersection(<coll.>) <span class="hljs-comment"># Or: <set> & <set></span>
<set> = <set>.difference(<coll.>) <span class="hljs-comment"># Or: <set> - <set></span>
<set> = <set>.symmetric_difference(<coll.>) <span class="hljs-comment"># Or: <set> ^ <set></span>
<bool> = <set>.issubset(<coll.>) <span class="hljs-comment"># Or: <set> <= <set></span>
<bool> = <set>.issuperset(<coll.>) <span class="hljs-comment"># Or: <set> >= <set></span>
</code></pre>
<pre><code class="python language-python hljs"><el> = <set>.pop() <span class="hljs-comment"># Raises KeyError if empty.</span>
<set>.remove(<el>) <span class="hljs-comment"># Raises KeyError if missing.</span>
<set>.discard(<el>) <span class="hljs-comment"># Doesn't raise an error.</span>
</code></pre>
<div><h3 id="frozenset">Frozen Set</h3><ul>
<li><strong>Is immutable and hashable.</strong></li>
<li><strong>That means it can be used as a key in a dictionary or as an element in a set.</strong></li>
</ul><pre><code class="python language-python hljs"><frozenset> = frozenset(<collection>)
</code></pre></div>
<div><h2 id="tuple"><a href="#tuple" name="tuple">#</a>Tuple</h2><p><strong>Tuple is an immutable and hashable list.</strong></p><pre><code class="python language-python hljs"><tuple> = () <span class="hljs-comment"># Empty tuple.</span>
<tuple> = (<el>,) <span class="hljs-comment"># Or: <el>,</span>
<tuple> = (<el_1>, <el_2> [, ...]) <span class="hljs-comment"># Or: <el_1>, <el_2> [, ...]</span>
</code></pre></div>
<div><h3 id="namedtuple">Named Tuple</h3><p><strong>Tuple's subclass with named elements.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
<span class="hljs-meta">>>> </span>Point = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>)
<span class="hljs-meta">>>> </span>p = Point(<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>)
<span class="hljs-meta">>>> </span>print(p)
Point(x=<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>)
<span class="hljs-meta">>>> </span>p[<span class="hljs-number">0</span>], p.x
(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>)
</code></pre></div>
<div><h2 id="range"><a href="#range" name="range">#</a>Range</h2><p><strong>Immutable and hashable sequence of integers.</strong></p><pre><code class="python language-python hljs"><range> = range(stop) <span class="hljs-comment"># I.e. range(to_exclusive).</span>
<range> = range(start, stop) <span class="hljs-comment"># I.e. range(from_inclusive, to_exclusive).</span>
<range> = range(start, stop, ±step) <span class="hljs-comment"># I.e. range(from_inclusive, to_exclusive, ±step).</span>
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>[i <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">3</span>)]
[<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>]
</code></pre>
<div><h2 id="enumerate"><a href="#enumerate" name="enumerate">#</a>Enumerate</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">for</span> i, el <span class="hljs-keyword">in</span> enumerate(<coll>, start=<span class="hljs-number">0</span>): <span class="hljs-comment"># Returns next element and its index on each pass.</span>
...
</code></pre></div>
<div><h2 id="iterator"><a href="#iterator" name="iterator">#</a>Iterator</h2><p><strong>Potentially endless stream of elements.</strong></p><pre><code class="python language-python hljs"><iter> = iter(<collection>) <span class="hljs-comment"># `iter(<iter>)` returns unmodified iterator.</span>
<iter> = iter(<function>, to_exclusive) <span class="hljs-comment"># A sequence of return values until 'to_exclusive'.</span>
<el> = next(<iter> [, default]) <span class="hljs-comment"># Raises StopIteration or returns 'default' on end.</span>
<list> = list(<iter>) <span class="hljs-comment"># Returns a list of iterator's remaining elements.</span>
</code></pre></div>
<div><h3 id="itertools">Itertools</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> itertools <span class="hljs-keyword">as</span> it
</code></pre></div>
<pre><code class="python language-python hljs"><iter> = it.count(start=<span class="hljs-number">0</span>, step=<span class="hljs-number">1</span>) <span class="hljs-comment"># Returns updated value endlessly. Accepts floats.</span>
<iter> = it.repeat(<el> [, times]) <span class="hljs-comment"># Returns element endlessly or 'times' times.</span>
<iter> = it.cycle(<collection>) <span class="hljs-comment"># Repeats the sequence endlessly.</span>
</code></pre>
<pre><code class="python language-python hljs"><iter> = it.chain(<coll>, <coll> [, ...]) <span class="hljs-comment"># Empties collections in order (figuratively).</span>
<iter> = it.chain.from_iterable(<coll>) <span class="hljs-comment"># Empties collections inside a collection in order.</span>
</code></pre>
<pre><code class="python language-python hljs"><iter> = it.islice(<coll>, to_exclusive) <span class="hljs-comment"># Only returns first 'to_exclusive' elements.</span>
<iter> = it.islice(<coll>, from_inc, …) <span class="hljs-comment"># `to_exclusive, +step_size`. Indices can be None.</span>
</code></pre>
<div><h2 id="generator"><a href="#generator" name="generator">#</a>Generator</h2><ul>
<li><strong>Any function that contains a yield statement returns a generator.</strong></li>
<li><strong>Generators and iterators are interchangeable.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">count</span><span class="hljs-params">(start, step)</span>:</span>
<span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
<span class="hljs-keyword">yield</span> start
start += step
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>counter = count(<span class="hljs-number">10</span>, <span class="hljs-number">2</span>)
<span class="hljs-meta">>>> </span>next(counter), next(counter), next(counter)
(<span class="hljs-number">10</span>, <span class="hljs-number">12</span>, <span class="hljs-number">14</span>)
</code></pre>
<div><h2 id="type"><a href="#type" name="type">#</a>Type</h2><ul>
<li><strong>Everything is an object.</strong></li>
<li><strong>Every object has a type.</strong></li>
<li><strong>Type and class are synonymous.</strong></li>
</ul><pre><code class="python language-python hljs"><type> = type(<el>) <span class="hljs-comment"># Or: <el>.__class__</span>
<bool> = isinstance(<el>, <type>) <span class="hljs-comment"># Or: issubclass(type(<el>), <type>)</span>
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>type(<span class="hljs-string">'a'</span>), <span class="hljs-string">'a'</span>.__class__, str
(<<span class="hljs-class"><span class="hljs-title">class</span> '<span class="hljs-title">str</span>'>, <<span class="hljs-title">class</span> '<span class="hljs-title">str</span>'>, <<span class="hljs-title">class</span> '<span class="hljs-title">str</span>'>)
</span></code></pre>
<div><h4 id="sometypesdonothavebuiltinnamessotheymustbeimported">Some types do not have built-in names, so they must be imported:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> types <span class="hljs-keyword">import</span> FunctionType, MethodType, LambdaType, GeneratorType, ModuleType
</code></pre></div>
<div><h3 id="abstractbaseclasses">Abstract Base Classes</h3><p><strong>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().</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> collections.abc <span class="hljs-keyword">import</span> Iterable, Collection, Sequence
<span class="hljs-meta">>>> </span>isinstance([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>], Iterable)
<span class="hljs-keyword">True</span>
</code></pre></div>
<pre><code class="text language-text">┏━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┓
┃ │ Iterable │ Collection │ Sequence ┃
┠──────────────────┼────────────┼────────────┼────────────┨
┃ list, range, str │ ✓ │ ✓ │ ✓ ┃
┃ dict, set │ ✓ │ ✓ │ ┃
┃ iter │ ✓ │ │ ┃
┗━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┛
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-keyword">from</span> numbers <span class="hljs-keyword">import</span> Number, Complex, Real, Rational, Integral
<span class="hljs-meta">>>> </span>isinstance(<span class="hljs-number">123</span>, Number)
<span class="hljs-keyword">True</span>
</code></pre>
<pre><code class="text language-text">┏━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┓
┃ │ Number │ Complex │ Real │ Rational │ Integral ┃
┠────────────────────┼──────────┼──────────┼──────────┼──────────┼──────────┨
┃ int │ ✓ │ ✓ │ ✓ │ ✓ │ ✓ ┃
┃ fractions.Fraction │ ✓ │ ✓ │ ✓ │ ✓ │ ┃
┃ float │ ✓ │ ✓ │ ✓ │ │ ┃
┃ complex │ ✓ │ ✓ │ │ │ ┃
┃ decimal.Decimal │ ✓ │ │ │ │ ┃
┗━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┛
</code></pre>
<div><h2 id="string"><a href="#string" name="string">#</a>String</h2><p><strong>Immutable sequence of characters.</strong></p><pre><code class="python language-python hljs"><str> = <str>.strip() <span class="hljs-comment"># Strips all whitespace characters from both ends.</span>
<str> = <str>.strip(<span class="hljs-string">'<chars>'</span>) <span class="hljs-comment"># Strips passed characters. Also lstrip/rstrip().</span>
</code></pre></div>
<pre><code class="python language-python hljs"><list> = <str>.split() <span class="hljs-comment"># Splits on one or more whitespace characters.</span>
<list> = <str>.split(sep=<span class="hljs-keyword">None</span>, maxsplit=<span class="hljs-number">-1</span>) <span class="hljs-comment"># Splits on 'sep' str at most 'maxsplit' times.</span>
<list> = <str>.splitlines(keepends=<span class="hljs-keyword">False</span>) <span class="hljs-comment"># On [\n\r\f\v\x1c-\x1e\x85\u2028\u2029] and \r\n.</span>
<str> = <str>.join(<coll_of_strings>) <span class="hljs-comment"># Joins elements using string as a separator.</span>
</code></pre>
<pre><code class="python language-python hljs"><bool> = <sub_str> <span class="hljs-keyword">in</span> <str> <span class="hljs-comment"># Checks if string contains the substring.</span>
<bool> = <str>.startswith(<sub_str>) <span class="hljs-comment"># Pass tuple of strings for multiple options.</span>
<int> = <str>.find(<sub_str>) <span class="hljs-comment"># Returns start index of the first match or -1.</span>
<int> = <str>.index(<sub_str>) <span class="hljs-comment"># Same, but raises ValueError if there's no match.</span>
</code></pre>
<pre><code class="python language-python hljs"><str> = <str>.lower() <span class="hljs-comment"># Changes the case. Also upper/capitalize/title().</span>
<str> = <str>.replace(old, new [, count]) <span class="hljs-comment"># Replaces 'old' with 'new' at most 'count' times.</span>
<str> = <str>.translate(<table>) <span class="hljs-comment"># Use `str.maketrans(<dict>)` to generate table.</span>
</code></pre>
<pre><code class="python language-python hljs"><str> = chr(<int>) <span class="hljs-comment"># Converts int to Unicode character.</span>
<int> = ord(<str>) <span class="hljs-comment"># Converts Unicode character to int.</span>
</code></pre>
<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'unicodedata.normalize("NFC", <str>)'</span></code> on strings like <code class="python hljs"><span class="hljs-string">'Motörhead'</span></code> before comparing them to other strings, because <code class="python hljs"><span class="hljs-string">'ö'</span></code> can be stored as one or two characters.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'NFC'</span></code> converts such characters to a single character, while <code class="python hljs"><span class="hljs-string">'NFD'</span></code> converts them to two.</strong></li>
</ul>
<div><h3 id="propertymethods">Property Methods</h3><pre><code class="python language-python hljs"><bool> = <str>.isdecimal() <span class="hljs-comment"># Checks for [0-9]. Also [०-९] and [٠-٩].</span>
<bool> = <str>.isdigit() <span class="hljs-comment"># Checks for [²³¹…] and isdecimal().</span>
<bool> = <str>.isnumeric() <span class="hljs-comment"># Checks for [¼½¾…], [零〇一…] and isdigit().</span>
<bool> = <str>.isalnum() <span class="hljs-comment"># Checks for [a-zA-Z…] and isnumeric().</span>
<bool> = <str>.isprintable() <span class="hljs-comment"># Checks for [ !#$%…] and isalnum().</span>
<bool> = <str>.isspace() <span class="hljs-comment"># Checks for [ \t\n\r\f\v\x1c-\x1f\x85\xa0…].</span>
</code></pre></div>
<div><h2 id="regex"><a href="#regex" name="regex">#</a>Regex</h2><p><strong>Functions for regular expression matching.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> re
<str> = re.sub(<span class="hljs-string">r'<regex>'</span>, new, text, count=<span class="hljs-number">0</span>) <span class="hljs-comment"># Substitutes all occurrences with 'new'.</span>
<list> = re.findall(<span class="hljs-string">r'<regex>'</span>, text) <span class="hljs-comment"># Returns all occurrences as strings.</span>
<list> = re.split(<span class="hljs-string">r'<regex>'</span>, text, maxsplit=<span class="hljs-number">0</span>) <span class="hljs-comment"># Add brackets around regex to keep matches.</span>
<Match> = re.search(<span class="hljs-string">r'<regex>'</span>, text) <span class="hljs-comment"># First occurrence of the pattern or None.</span>
<Match> = re.match(<span class="hljs-string">r'<regex>'</span>, text) <span class="hljs-comment"># Searches only at the beginning of the text.</span>
<iter> = re.finditer(<span class="hljs-string">r'<regex>'</span>, text) <span class="hljs-comment"># Returns all occurrences as Match objects.</span>
</code></pre></div>
<ul>
<li><strong>Raw string literals do not interpret escape sequences, thus enabling us to use regex-specific escape sequences that cause SyntaxWarning in normal string literals (since 3.12).</strong></li>
<li><strong>Argument 'new' of re.sub() can be a function that accepts Match object and returns a str.</strong></li>
<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.IGNORECASE'</span></code> can be used with all functions.</strong></li>
<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.MULTILINE'</span></code> makes <code class="python hljs"><span class="hljs-string">'^'</span></code> and <code class="python hljs"><span class="hljs-string">'$'</span></code> match the start/end of each line.</strong></li>
<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.DOTALL'</span></code> makes <code class="python hljs"><span class="hljs-string">'.'</span></code> also accept the <code class="python hljs"><span class="hljs-string">'\n'</span></code>.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'re.compile(<regex>)'</span></code> returns a Pattern object with methods sub(), findall(), etc.</strong></li>
</ul>
<div><h3 id="matchobject">Match Object</h3><pre><code class="python language-python hljs"><str> = <Match>.group() <span class="hljs-comment"># Returns the whole match. Also group(0).</span>
<str> = <Match>.group(<span class="hljs-number">1</span>) <span class="hljs-comment"># Returns part inside the first brackets.</span>
<tuple> = <Match>.groups() <span class="hljs-comment"># Returns all bracketed parts.</span>
<int> = <Match>.start() <span class="hljs-comment"># Returns start index of the match.</span>
<int> = <Match>.end() <span class="hljs-comment"># Returns exclusive end index of the match.</span>
</code></pre></div>
<div><h3 id="specialsequences">Special Sequences</h3><pre><code class="python language-python hljs"><span class="hljs-string">'\d'</span> == <span class="hljs-string">'[0-9]'</span> <span class="hljs-comment"># Also [०-९…]. Matches a decimal character.</span>
<span class="hljs-string">'\w'</span> == <span class="hljs-string">'[a-zA-Z0-9_]'</span> <span class="hljs-comment"># Also [ª²³…]. Matches an alphanumeric or _.</span>
<span class="hljs-string">'\s'</span> == <span class="hljs-string">'[ \t\n\r\f\v]'</span> <span class="hljs-comment"># Also [\x1c-\x1f…]. Matches a whitespace.</span>
</code></pre></div>
<ul>
<li><strong>By default, decimal characters and alphanumerics from all alphabets are matched unless <code class="python hljs"><span class="hljs-string">'flags=re.ASCII'</span></code> is used. It restricts special sequence matches to the first 128 Unicode characters and also prevents <code class="python hljs"><span class="hljs-string">'\s'</span></code> from accepting <code class="python hljs"><span class="hljs-string">'\x1c'</span></code>, <code class="python hljs"><span class="hljs-string">'\x1d'</span></code>, <code class="python hljs"><span class="hljs-string">'\x1e'</span></code> and <code class="python hljs"><span class="hljs-string">'\x1f'</span></code> (non-printable characters that divide text into files, tables, rows and fields, respectively).</strong></li>
<li><strong>Use a capital letter for negation (all non-ASCII characters will be matched when used in combination with ASCII flag).</strong></li>
</ul>
<div><h2 id="format"><a href="#format" name="format">#</a>Format</h2><pre><code class="python hljs"><str> = <span class="hljs-string">f'<span class="hljs-subst">{<el_1>}</span>, <span class="hljs-subst">{<el_2>}</span>'</span> <span class="hljs-comment"># Curly brackets can also contain expressions.</span>
<str> = <span class="hljs-string">'{}, {}'</span>.format(<el_1>, <el_2>) <span class="hljs-comment"># Or: '{0}, {a}'.format(<el_1>, a=<el_2>)</span>
<str> = <span class="hljs-string">'%s, %s'</span> % (<el_1>, <el_2>) <span class="hljs-comment"># Redundant and inferior C-style formatting.</span>
</code></pre></div>
<div><h3 id="example">Example</h3><pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>Person = collections.namedtuple(<span class="hljs-string">'Person'</span>, <span class="hljs-string">'name height'</span>)
<span class="hljs-meta">>>> </span>person = Person(<span class="hljs-string">'Jean-Luc'</span>, <span class="hljs-number">187</span>)
<span class="hljs-meta">>>> </span><span class="hljs-string">f'<span class="hljs-subst">{person.name}</span> is <span class="hljs-subst">{person.height / <span class="hljs-number">100</span>}</span> meters tall.'</span>
<span class="hljs-string">'Jean-Luc is 1.87 meters tall.'</span>
</code></pre></div>
<div><h3 id="generaloptions">General Options</h3><pre><code class="python language-python hljs">{<el>:<<span class="hljs-number">10</span>} <span class="hljs-comment"># '<el> '</span>
{<el>:^<span class="hljs-number">10</span>} <span class="hljs-comment"># ' <el> '</span>
{<el>:><span class="hljs-number">10</span>} <span class="hljs-comment"># ' <el>'</span>
{<el>:.<<span class="hljs-number">10</span>} <span class="hljs-comment"># '<el>......'</span>
{<el>:<span class="hljs-number">0</span>} <span class="hljs-comment"># '<el>'</span>
</code></pre></div>
<ul>
<li><strong>Objects are rendered using <code class="python hljs"><span class="hljs-string">'format(<el>, "<options>")'</span></code>.</strong></li>
<li><strong>Options can be generated dynamically: <code class="python hljs"><span class="hljs-string">f'<span class="hljs-subst">{<el>:{<str/int>}</span>[…]}'</span></code>.</strong></li>
<li><strong>Adding <code class="python hljs"><span class="hljs-string">'='</span></code> to the expression prepends it to the output: <code class="python hljs"><span class="hljs-string">f'<span class="hljs-subst">{<span class="hljs-number">1</span>+<span class="hljs-number">1</span>=}</span>'</span></code> returns <code class="python hljs"><span class="hljs-string">'1+1=2'</span></code>.</strong></li>
<li><strong>Adding <code class="python hljs"><span class="hljs-string">'!r'</span></code> to the expression converts object to string by calling its <a href="#class">repr()</a> method.</strong></li>
</ul>
<div><h3 id="strings">Strings</h3><pre><code class="python language-python hljs">{<span class="hljs-string">'abcde'</span>:<span class="hljs-number">10</span>} <span class="hljs-comment"># 'abcde '</span>
{<span class="hljs-string">'abcde'</span>:<span class="hljs-number">10.3</span>} <span class="hljs-comment"># 'abc '</span>
{<span class="hljs-string">'abcde'</span>:<span class="hljs-number">.3</span>} <span class="hljs-comment"># 'abc'</span>
{<span class="hljs-string">'abcde'</span>!r:<span class="hljs-number">10</span>} <span class="hljs-comment"># "'abcde' "</span>
</code></pre></div>
<div><h3 id="numbers-1">Numbers</h3><pre><code class="python language-python hljs">{<span class="hljs-number">123456</span>:<span class="hljs-number">10</span>} <span class="hljs-comment"># ' 123456'</span>
{<span class="hljs-number">123456</span>:<span class="hljs-number">10</span>,} <span class="hljs-comment"># ' 123,456'</span>
{<span class="hljs-number">123456</span>:<span class="hljs-number">10</span>_} <span class="hljs-comment"># ' 123_456'</span>
{<span class="hljs-number">123456</span>:+<span class="hljs-number">10</span>} <span class="hljs-comment"># ' +123456'</span>
{<span class="hljs-number">123456</span>:=+<span class="hljs-number">10</span>} <span class="hljs-comment"># '+ 123456'</span>
{<span class="hljs-number">123456</span>: } <span class="hljs-comment"># ' 123456'</span>
{<span class="hljs-number">-123456</span>: } <span class="hljs-comment"># '-123456'</span>
</code></pre></div>
<div><h3 id="floats">Floats</h3><pre><code class="python language-python hljs">{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>} <span class="hljs-comment"># ' 1.23'</span>
{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>f} <span class="hljs-comment"># ' 1.235'</span>
{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>e} <span class="hljs-comment"># ' 1.235e+00'</span>
{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>%} <span class="hljs-comment"># ' 123.456%'</span>
</code></pre></div>
<div><h4 id="comparisonofpresentationtypes">Comparison of presentation types:</h4><pre><code class="text language-text">┏━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┓
┃ │ {<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%' ┃
┗━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┛
</code></pre></div>
<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'{<float>:g}'</span></code> is <code class="python hljs"><span class="hljs-string">'{<float>:.6}'</span></code> with stripped zeros, exponent starting at <code class="python hljs"><span class="hljs-string">'1e+06'</span></code>.</strong></li>
<li><strong>When both rounding up and rounding down are possible, the one that returns result with even last digit is chosen. That makes <code class="python hljs"><span class="hljs-string">'{6.5:.0f}'</span></code> a <code class="python hljs"><span class="hljs-string">'6'</span></code> and <code class="python hljs"><span class="hljs-string">'{7.5:.0f}'</span></code> an <code class="python hljs"><span class="hljs-string">'8'</span></code>.</strong></li>
<li><strong>This rule only effects numbers that can be represented exactly by a float (<code class="python hljs"><span class="hljs-number">.5</span></code>, <code class="python hljs"><span class="hljs-number">.25</span></code>, …).</strong></li>
</ul>
<div><h3 id="ints">Ints</h3><pre><code class="python language-python hljs">{<span class="hljs-number">90</span>:c} <span class="hljs-comment"># 'Z'. Unicode character with value 90.</span>
{<span class="hljs-number">90</span>:b} <span class="hljs-comment"># '1011010'. Binary representation of the int.</span>
{<span class="hljs-number">90</span>:X} <span class="hljs-comment"># '5A'. Hexadecimal with upper-case letters.</span>
</code></pre></div>
<div><h2 id="numbers"><a href="#numbers" name="numbers">#</a>Numbers</h2><pre><code class="python language-python hljs"><int> = int(<float/str/bool>) <span class="hljs-comment"># Or: math.trunc(<float>)</span>
<float> = float(<int/str/bool>) <span class="hljs-comment"># Or: <int/float>e±<int></span>
<complex> = complex(real=<span class="hljs-number">0</span>, imag=<span class="hljs-number">0</span>) <span class="hljs-comment"># Or: <int/float> ± <int/float>j</span>
<Fraction> = fractions.Fraction(<span class="hljs-number">0</span>, <span class="hljs-number">1</span>) <span class="hljs-comment"># Or: Fraction(numerator=0, denominator=1)</span>
<Decimal> = decimal.Decimal(<str/int>) <span class="hljs-comment"># Or: Decimal((sign, digits, exponent))</span>
</code></pre></div>
<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'int(<str>)'</span></code> and <code class="python hljs"><span class="hljs-string">'float(<str>)'</span></code> raise ValueError on malformed strings.</strong></li>
<li><strong>Decimal numbers are stored exactly, unlike most floats where <code class="python hljs"><span class="hljs-string">'1.1 + 2.2 != 3.3'</span></code>.</strong></li>
<li><strong>Floats can be compared with: <code class="python hljs"><span class="hljs-string">'math.isclose(<float>, <float>)'</span></code>.</strong></li>
<li><strong>Precision of decimal operations is set with: <code class="python hljs"><span class="hljs-string">'decimal.getcontext().prec = <int>'</span></code>.</strong></li>
<li><strong>Bools can be used anywhere ints can, because bool is a subclass of int: <code class="python hljs"><span class="hljs-string">'True + 1 == 2'</span></code>.</strong></li>
</ul>
<div><h3 id="builtinfunctions">Built-in Functions</h3><pre><code class="python language-python hljs"><num> = pow(<num>, <num>) <span class="hljs-comment"># Or: <number> ** <number></span>
<num> = abs(<num>) <span class="hljs-comment"># <float> = abs(<complex>)</span>
<num> = round(<num> [, ±ndigits]) <span class="hljs-comment"># Also math.floor/ceil(<number>).</span>
<num> = min(<collection>) <span class="hljs-comment"># Also max(<num>, <num> [, ...]).</span>
<num> = sum(<collection>) <span class="hljs-comment"># Also math.prod(<collection>).</span>
</code></pre></div>
<div><h3 id="math">Math</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> pi, inf, nan, isnan <span class="hljs-comment"># `inf*0` and `nan+1` return nan.</span>
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> sqrt, factorial <span class="hljs-comment"># `sqrt(-1)` raises ValueError.</span>
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> sin, cos, tan <span class="hljs-comment"># Also: asin, degrees, radians.</span>
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> log, log10, log2 <span class="hljs-comment"># Log accepts base as second arg.</span>
</code></pre></div>
<div><h3 id="statistics">Statistics</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> statistics <span class="hljs-keyword">import</span> mean, median, mode <span class="hljs-comment"># Mode returns the most common value.</span>
<span class="hljs-keyword">from</span> statistics <span class="hljs-keyword">import</span> variance, stdev <span class="hljs-comment"># Also: pvariance, pstdev, quantiles.</span>
</code></pre></div>
<div><h3 id="random">Random</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> random, randint, uniform <span class="hljs-comment"># Also: gauss, choice, shuffle, seed.</span>
</code></pre></div>
<pre><code class="python language-python hljs"><float> = random() <span class="hljs-comment"># Returns a float inside [0, 1).</span>
<num> = randint/uniform(a, b) <span class="hljs-comment"># Returns an int/float inside [a, b].</span>
<float> = gauss(mean, stdev) <span class="hljs-comment"># Also triangular(low, high, mode).</span>
<el> = choice(<sequence>) <span class="hljs-comment"># Keeps it intact. Also sample(pop, k).</span>
shuffle(<list>) <span class="hljs-comment"># Shuffles the list in place.</span>
</code></pre>
<div><h3 id="hexadecimalnumbers">Hexadecimal Numbers</h3><pre><code class="python language-python hljs"><int> = ±<span class="hljs-number">0x</span><hex> <span class="hljs-comment"># Or: ±0b<bin></span>
<int> = int(<span class="hljs-string">'±<hex>'</span>, <span class="hljs-number">16</span>) <span class="hljs-comment"># Or: int('±<bin>', 2)</span>
<int> = int(<span class="hljs-string">'±0x<hex>'</span>, <span class="hljs-number">0</span>) <span class="hljs-comment"># Or: int('±0b<bin>', 0)</span>
<str> = hex(<int>) <span class="hljs-comment"># Returns '[-]0x<hex>'. Also bin().</span>
</code></pre></div>
<div><h3 id="bitwiseoperators">Bitwise Operators</h3><pre><code class="python language-python hljs"><int> = <int> & <int> <span class="hljs-comment"># And (0b1100 & 0b1010 == 0b1000).</span>
<int> = <int> | <int> <span class="hljs-comment"># Or (0b1100 | 0b1010 == 0b1110).</span>
<int> = <int> ^ <int> <span class="hljs-comment"># Xor (0b1100 ^ 0b1010 == 0b0110).</span>
<int> = <int> << n_bits <span class="hljs-comment"># Left shift. Use >> for right.</span>
<int> = ~<int> <span class="hljs-comment"># Not. Also -<int> - 1.</span>
</code></pre></div>
<div><h2 id="combinatorics"><a href="#combinatorics" name="combinatorics">#</a>Combinatorics</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> itertools <span class="hljs-keyword">as</span> it
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>list(it.product(<span class="hljs-string">'abc'</span>, repeat=<span class="hljs-number">2</span>)) <span class="hljs-comment"># a b c</span>
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>), <span class="hljs-comment"># a x x x</span>
(<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>), <span class="hljs-comment"># b x x x</span>
(<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'c'</span>)] <span class="hljs-comment"># c x x x</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>list(it.permutations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>)) <span class="hljs-comment"># a b c</span>
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>), <span class="hljs-comment"># a . x x</span>
(<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>), <span class="hljs-comment"># b x . x</span>
(<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>)] <span class="hljs-comment"># c x x .</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>list(it.combinations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>)) <span class="hljs-comment"># a b c</span>
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>), <span class="hljs-comment"># a . x x</span>
(<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>) <span class="hljs-comment"># b . . x</span>
] <span class="hljs-comment"># c . . .</span>
</code></pre>
<div><h2 id="datetime"><a href="#datetime" name="datetime">#</a>Datetime</h2><p><strong>Provides 'date', 'time', 'datetime' and 'timedelta' classes. All are immutable and hashable.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install python-dateutil</span>
<span class="hljs-keyword">from</span> datetime <span class="hljs-keyword">import</span> date, time, datetime, timedelta, timezone
<span class="hljs-keyword">import</span> zoneinfo, dateutil.tz
</code></pre></div>
<pre><code class="python language-python apache hljs"><D> = date(year, month, day) <span class="hljs-comment"># Only accepts valid dates from 1 to 9999 AD.</span>
<T> = time(hour=<span class="hljs-number">0</span>, minute=<span class="hljs-number">0</span>, second=<span class="hljs-number">0</span>) <span class="hljs-comment"># Also: `microsecond=0, tzinfo=None, fold=0`.</span>
<DT> = datetime(year, month, day, hour=<span class="hljs-number">0</span>) <span class="hljs-comment"># Also: `minute=0, second=0, microsecond=0, …`.</span>
<TD> = timedelta(weeks=<span class="hljs-number">0</span>, days=<span class="hljs-number">0</span>, hours=<span class="hljs-number">0</span>) <span class="hljs-comment"># Also: `minutes=0, seconds=0, microseconds=0`.</span>
</code></pre>
<ul>
<li><strong>Times and datetimes that have defined timezone are called aware and ones that don't, naive. If object is naive, it is presumed to be in the system's timezone!</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'fold=1'</span></code> means the second pass in case of time jumping back for one hour.</strong></li>
<li><strong>Timedelta normalizes arguments to ±days, seconds (< 86 400) and microseconds (< 1M). Its str() method returns <code class="python hljs"><span class="hljs-string">'[±D, ]H:MM:SS[.…]'</span></code> and total_seconds() a float of all seconds.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'<D/DT>.weekday()'</span></code> to get the day of the week as an int, with Monday being 0.</strong></li>
</ul>
<div><h3 id="now">Now</h3><pre><code class="python language-python hljs"><D/DTn> = D/DT.today() <span class="hljs-comment"># Current local date or naive DT. Also DT.now().</span>
<DTa> = DT.now(<tzinfo>) <span class="hljs-comment"># Aware DT from current time in passed timezone.</span>
</code></pre></div>
<ul>
<li><strong>To extract time use <code class="python hljs"><span class="hljs-string">'<DTn>.time()'</span></code>, <code class="python hljs"><span class="hljs-string">'<DTa>.time()'</span></code> or <code class="python hljs"><span class="hljs-string">'<DTa>.timetz()'</span></code>.</strong></li>
</ul>
<div><h3 id="timezone">Timezone</h3><pre><code class="python language-python apache hljs"><tzinfo> = timezone.utc <span class="hljs-comment"># London without daylight saving time (DST).</span>
<tzinfo> = timezone(<timedelta>) <span class="hljs-comment"># Timezone with fixed offset from UTC.</span>
<tzinfo> = dateutil.tz.tzlocal() <span class="hljs-comment"># Local timezone with dynamic offset from UTC.</span>
<tzinfo> = zoneinfo.ZoneInfo(<span class="hljs-string">'<iana_key>'</span>) <span class="hljs-comment"># 'Continent/City_Name' zone with dynamic offset.</span>
<DTa> = <DT>.astimezone([<tzinfo>]) <span class="hljs-comment"># Converts DT to the passed or local fixed zone.</span>
<Ta/DTa> = <T/DT>.replace(tzinfo=<tzinfo>) <span class="hljs-comment"># Changes object's timezone without conversion.</span>
</code></pre></div>
<ul>
<li><strong>Timezones returned by tzlocal(), ZoneInfo() and implicit local timezone of naive objects have offsets that vary through time due to DST and historical changes of the base offset.</strong></li>
<li><strong>To get ZoneInfo() to work on Windows run <code class="python hljs"><span class="hljs-string">'> pip3 install tzdata'</span></code>.</strong></li>
</ul>
<div><h3 id="encode">Encode</h3><pre><code class="python language-python apache hljs"><D/T/DT> = D/T/DT.fromisoformat(<str>) <span class="hljs-comment"># Object from ISO string. Raises ValueError.</span>
<DT> = DT.strptime(<str>, <span class="hljs-string">'<format>'</span>) <span class="hljs-comment"># Datetime from custom string. See Format.</span>
<D/DTn> = D/DT.fromordinal(<int>) <span class="hljs-comment"># D/DT from days since the Gregorian NYE 1.</span>
<DTn> = DT.fromtimestamp(<float>) <span class="hljs-comment"># Local naive DT from seconds since the Epoch.</span>
<DTa> = DT.fromtimestamp(<float>, <tz>) <span class="hljs-comment"># Aware datetime from seconds since the Epoch.</span>
</code></pre></div>
<ul>
<li><strong>ISO strings come in following forms: <code class="python hljs"><span class="hljs-string">'YYYY-MM-DD'</span></code>, <code class="python hljs"><span class="hljs-string">'HH:MM:SS.mmmuuu[±HH:MM]'</span></code>, or both separated by an arbitrary character. All parts following the hours are optional.</strong></li>
<li><strong>Python uses the Unix Epoch: <code class="python hljs"><span class="hljs-string">'1970-01-01 00:00 UTC'</span></code>, <code class="python hljs"><span class="hljs-string">'1970-01-01 01:00 CET'</span></code>, …</strong></li>
</ul>
<div><h3 id="decode">Decode</h3><pre><code class="python language-python hljs"><str> = <D/T/DT>.isoformat(sep=<span class="hljs-string">'T'</span>) <span class="hljs-comment"># Also `timespec='auto/hours/minutes/seconds/…'`.</span>
<str> = <D/T/DT>.strftime(<span class="hljs-string">'<format>'</span>) <span class="hljs-comment"># Custom string representation of the object.</span>
<int> = <D/DT>.toordinal() <span class="hljs-comment"># Days since Gregorian NYE 1, ignoring time and tz.</span>
<float> = <DTn>.timestamp() <span class="hljs-comment"># Seconds since the Epoch, from local naive DT.</span>
<float> = <DTa>.timestamp() <span class="hljs-comment"># Seconds since the Epoch, from aware datetime.</span>
</code></pre></div>
<div><h3 id="format-1">Format</h3><pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>dt = datetime.strptime(<span class="hljs-string">'2025-08-14 23:39:00.00 +0200'</span>, <span class="hljs-string">'%Y-%m-%d %H:%M:%S.%f %z'</span>)
<span class="hljs-meta">>>> </span>dt.strftime(<span class="hljs-string">"%dth of %B '%y (%a), %I:%M %p %Z"</span>)
<span class="hljs-string">"14th of August '25 (Thu), 11:39 PM UTC+02:00"</span>
</code></pre></div>
<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'%z'</span></code> accepts <code class="python hljs"><span class="hljs-string">'±HH[:]MM'</span></code> and returns <code class="python hljs"><span class="hljs-string">'±HHMM'</span></code> or empty string if object is naive.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'%Z'</span></code> accepts <code class="python hljs"><span class="hljs-string">'UTC/GMT'</span></code> and local timezone's code and returns timezone's name, <code class="python hljs"><span class="hljs-string">'UTC[±HH:MM]'</span></code> if timezone is nameless, or an empty string if object is naive.</strong></li>
</ul>
<div><h3 id="arithmetics">Arithmetics</h3><pre><code class="python language-python apache hljs"><bool> = <D/T/DTn> > <D/T/DTn> <span class="hljs-comment"># Ignores time jumps (fold attribute). Also ==.</span>
<bool> = <DTa> > <DTa> <span class="hljs-comment"># Ignores time jumps if they share tzinfo object.</span>
<TD> = <D/DTn> - <D/DTn> <span class="hljs-comment"># Ignores jumps. Convert to UTC for actual delta.</span>
<TD> = <DTa> - <DTa> <span class="hljs-comment"># Ignores jumps if they share tzinfo object.</span>
<D/DT> = <D/DT> ± <TD> <span class="hljs-comment"># Returned datetime can fall into missing hour.</span>
<TD> = <TD> * <float> <span class="hljs-comment"># Also `<TD> = abs(<TD>)`, `<TD> = <TD> ± <TD>`.</span>
<float> = <TD> / <TD> <span class="hljs-comment"># Also `(<int>, <TD>) = divmod(<TD>, <TD>)`.</span>
</code></pre></div>
<div><h2 id="function"><a href="#function" name="function">#</a>Function</h2><p><strong>Independent block of code that returns a value when called.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <<span class="hljs-title">func_name</span>><span class="hljs-params">(<nondefault_args>)</span>:</span> ... <span class="hljs-comment"># E.g. `def func(x, y): ...`.</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <<span class="hljs-title">func_name</span>><span class="hljs-params">(<default_args>)</span>:</span> ... <span class="hljs-comment"># E.g. `def func(x=0, y=0): ...`.</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <<span class="hljs-title">func_name</span>><span class="hljs-params">(<nondefault_args>, <default_args>)</span>:</span> ... <span class="hljs-comment"># E.g. `def func(x, y=0): ...`.</span>
</code></pre></div>
<ul>
<li><strong>Function returns None if it doesn't encounter <code class="python hljs"><span class="hljs-string">'return <obj/exp>'</span></code> statement.</strong></li>
<li><strong>Run <code class="python hljs"><span class="hljs-string">'global <var_name>'</span></code> inside the function before assigning to global variable.</strong></li>
<li><strong>Default values are evaluated when function is first encountered in the scope. Any mutation of a mutable default value will persist between invocations!</strong></li>
</ul>
<div><h3 id="functioncall">Function Call</h3><pre><code class="python language-python hljs"><obj> = <function>(<positional_args>) <span class="hljs-comment"># E.g. `func(0, 0)`.</span>
<obj> = <function>(<keyword_args>) <span class="hljs-comment"># E.g. `func(x=0, y=0)`.</span>
<obj> = <function>(<positional_args>, <keyword_args>) <span class="hljs-comment"># E.g. `func(0, y=0)`.</span>
</code></pre></div>
<div><h2 id="splatoperator"><a href="#splatoperator" name="splatoperator">#</a>Splat Operator</h2><p><strong>Splat expands a collection into positional arguments, while splatty-splat expands a dictionary into keyword arguments.</strong></p><pre><code class="python language-python hljs">args, kwargs = (<span class="hljs-number">1</span>, <span class="hljs-number">2</span>), {<span class="hljs-string">'z'</span>: <span class="hljs-number">3</span>}
func(*args, **kwargs)
</code></pre></div>
<div><h4 id="isthesameas">Is the same as:</h4><pre><code class="python language-python hljs">func(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, z=<span class="hljs-number">3</span>)
</code></pre></div>
<div><h3 id="insidefunctiondefinition">Inside Function Definition</h3><p><strong>Splat combines zero or more positional arguments into a tuple, while splatty-splat combines zero or more keyword arguments into a dictionary.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(*a)</span>:</span>
<span class="hljs-meta">... </span> <span class="hljs-keyword">return</span> sum(a)
<span class="hljs-meta">... </span>
<span class="hljs-meta">>>> </span>add(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
<span class="hljs-number">6</span>
</code></pre></div>
<div><h4 id="allowedcompositionsofargumentsinsidefunctiondefinitionandthewaystheycanbecalled">Allowed compositions of arguments inside function definition and the ways they can be called:</h4><pre><code class="text language-text">┏━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━┓
┃ │ f(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>) │ f(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, z=<span class="hljs-number">3</span>) │ f(<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>, z=<span class="hljs-number">3</span>) │ f(x=<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>, z=<span class="hljs-number">3</span>) ┃
┠────────────────────┼────────────┼──────────────┼────────────────┼──────────────────┨
┃ <span class="hljs-title">f</span>(x, *args, **kw): │ ✓ │ ✓ │ ✓ │ ✓ ┃
┃ <span class="hljs-title">f</span>(*args, z, **kw): │ │ ✓ │ ✓ │ ✓ ┃
┃ <span class="hljs-title">f</span>(x, **kw): │ │ │ ✓ │ ✓ ┃
┃ <span class="hljs-title">f</span>(*, x, **kw): │ │ │ │ ✓ ┃
┗━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━┛
</code></pre></div>
<div><h3 id="otheruses">Other Uses</h3><pre><code class="python language-python hljs"><list> = [*<collection> [, ...]] <span class="hljs-comment"># Or: list(<coll>) [+ ...]</span>
<tuple> = (*<collection>, [...]) <span class="hljs-comment"># Or: tuple(<coll>) [+ ...]</span>
<set> = {*<collection> [, ...]} <span class="hljs-comment"># Or: set(<coll>) [| ...]</span>
<dict> = {**<dict> [, ...]} <span class="hljs-comment"># Or: <dict> | ...</span>
</code></pre></div>
<pre><code class="python language-python hljs">head, *body, tail = <collection> <span class="hljs-comment"># Head or tail can be omitted.</span>
</code></pre>
<div><h2 id="inline"><a href="#inline" name="inline">#</a>Inline</h2><div><h3 id="lambda">Lambda</h3><pre><code class="python language-python hljs"><func> = <span class="hljs-keyword">lambda</span>: <return_value> <span class="hljs-comment"># A single statement function.</span>
<func> = <span class="hljs-keyword">lambda</span> <arg_1>, <arg_2>: <return_value> <span class="hljs-comment"># Also allows default arguments.</span>
</code></pre></div></div>
<div><h3 id="comprehensions">Comprehensions</h3><pre><code class="python language-python hljs"><list> = [i+<span class="hljs-number">1</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)] <span class="hljs-comment"># Or: [1, 2, ..., 10]</span>
<iter> = (i <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>) <span class="hljs-keyword">if</span> i > <span class="hljs-number">5</span>) <span class="hljs-comment"># Or: iter([6, 7, 8, 9])</span>
<set> = {i+<span class="hljs-number">5</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)} <span class="hljs-comment"># Or: {5, 6, ..., 14}</span>
<dict> = {i: i*<span class="hljs-number">2</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)} <span class="hljs-comment"># Or: {0: 0, 1: 2, ..., 9: 18}</span>
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>[l+r <span class="hljs-keyword">for</span> l <span class="hljs-keyword">in</span> <span class="hljs-string">'abc'</span> <span class="hljs-keyword">for</span> r <span class="hljs-keyword">in</span> <span class="hljs-string">'abc'</span>] <span class="hljs-comment"># Inner loop is on the right side.</span>
[<span class="hljs-string">'aa'</span>, <span class="hljs-string">'ab'</span>, <span class="hljs-string">'ac'</span>, ..., <span class="hljs-string">'cc'</span>]
</code></pre>
<div><h3 id="mapfilterreduce">Map, Filter, Reduce</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> reduce
</code></pre></div>
<pre><code class="python language-python hljs"><iter> = map(<span class="hljs-keyword">lambda</span> x: x + <span class="hljs-number">1</span>, range(<span class="hljs-number">10</span>)) <span class="hljs-comment"># Or: iter([1, 2, ..., 10])</span>
<iter> = filter(<span class="hljs-keyword">lambda</span> x: x > <span class="hljs-number">5</span>, range(<span class="hljs-number">10</span>)) <span class="hljs-comment"># Or: iter([6, 7, 8, 9])</span>
<obj> = reduce(<span class="hljs-keyword">lambda</span> out, x: out + x, range(<span class="hljs-number">10</span>)) <span class="hljs-comment"># Or: 45</span>
</code></pre>
<div><h3 id="anyall">Any, All</h3><pre><code class="python language-python hljs"><bool> = any(<collection>) <span class="hljs-comment"># Is `bool(<el>)` True for any el?</span>
<bool> = all(<collection>) <span class="hljs-comment"># True for all? Also True if empty.</span>
</code></pre></div>
<div><h3 id="conditionalexpression">Conditional Expression</h3><pre><code class="python language-python hljs"><obj> = <exp> <span class="hljs-keyword">if</span> <condition> <span class="hljs-keyword">else</span> <exp> <span class="hljs-comment"># Only one expression is evaluated.</span>
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>[i <span class="hljs-keyword">if</span> i <span class="hljs-keyword">else</span> <span class="hljs-string">'zero'</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)] <span class="hljs-comment"># `any([0, '', [], None]) == False`</span>
[<span class="hljs-string">'zero'</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]
</code></pre>
<div><h3 id="andor">And, Or</h3><pre><code class="python language-python hljs"><obj> = <exp> <span class="hljs-keyword">and</span> <exp> [<span class="hljs-keyword">and</span> ...] <span class="hljs-comment"># Returns first false or last operand.</span>
<obj> = <exp> <span class="hljs-keyword">or</span> <exp> [<span class="hljs-keyword">or</span> ...] <span class="hljs-comment"># Returns first true or last operand.</span>
</code></pre></div>
<div><h3 id="walrusoperator">Walrus Operator</h3><pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>[i <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> <span class="hljs-string">'0123'</span> <span class="hljs-keyword">if</span> (i := int(a)) > <span class="hljs-number">0</span>] <span class="hljs-comment"># Assigns to variable mid-sentence.</span>
[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]
</code></pre></div>
<div><h3 id="namedtupleenumdataclass">Named Tuple, Enum, Dataclass</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
Point = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>) <span class="hljs-comment"># Creates tuple's subclass.</span>
point = Point(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>) <span class="hljs-comment"># Returns its instance.</span>
<span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum
Direction = Enum(<span class="hljs-string">'Direction'</span>, <span class="hljs-string">'N E S W'</span>) <span class="hljs-comment"># Creates Enum's subclass.</span>
direction = Direction.N <span class="hljs-comment"># Returns its member.</span>
<span class="hljs-keyword">from</span> dataclasses <span class="hljs-keyword">import</span> make_dataclass
Player = make_dataclass(<span class="hljs-string">'Player'</span>, [<span class="hljs-string">'loc'</span>, <span class="hljs-string">'dir'</span>]) <span class="hljs-comment"># Creates a class.</span>
player = Player(point, direction) <span class="hljs-comment"># Returns its instance.</span>
</code></pre></div>
<div><h2 id="imports"><a href="#imports" name="imports">#</a>Imports</h2><p><strong>Mechanism that makes code in one file available to another file.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> <module> <span class="hljs-comment"># Imports a built-in or '<module>.py'.</span>
<span class="hljs-keyword">import</span> <package> <span class="hljs-comment"># Imports a built-in or '<package>/__init__.py'.</span>
<span class="hljs-keyword">import</span> <package>.<module> <span class="hljs-comment"># Imports a built-in or '<package>/<module>.py'.</span>
</code></pre></div>
<ul>
<li><strong>Package is a collection of modules, but it can also define its own objects.</strong></li>
<li><strong>On a filesystem this corresponds to a directory of Python files with an optional init script.</strong></li>
<li><strong>Running <code class="python hljs"><span class="hljs-string">'import <package>'</span></code> does not automatically provide access to the package's modules unless they are explicitly imported in its init script.</strong></li>
<li><strong>Directory of the file that is passed to python command serves as a root of local imports.</strong></li>
<li><strong>For relative imports use <code class="python hljs"><span class="hljs-string">'from .[…][<pkg/module>[.…]] import <obj>'</span></code>.</strong></li>
</ul>
<div><h2 id="closure"><a href="#closure" name="closure">#</a>Closure</h2><p><strong>We have/get a closure in Python when a nested function references a value of its enclosing function and then the enclosing function returns its nested function.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_multiplier</span><span class="hljs-params">(a)</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(b)</span>:</span>
<span class="hljs-keyword">return</span> a * b
<span class="hljs-keyword">return</span> out
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>multiply_by_3 = get_multiplier(<span class="hljs-number">3</span>)
<span class="hljs-meta">>>> </span>multiply_by_3(<span class="hljs-number">10</span>)
<span class="hljs-number">30</span>
</code></pre>
<ul>
<li><strong>Any value that is referenced from within multiple nested functions gets shared.</strong></li>
</ul>
<div><h3 id="partial">Partial</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> partial
<function> = partial(<function> [, <arg_1> [, ...]])
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">multiply</span><span class="hljs-params">(a, b)</span>:</span>
<span class="hljs-meta">... </span> <span class="hljs-keyword">return</span> a * b
<span class="hljs-meta">>>> </span>multiply_by_3 = partial(multiply, <span class="hljs-number">3</span>)
<span class="hljs-meta">>>> </span>multiply_by_3(<span class="hljs-number">10</span>)
<span class="hljs-number">30</span>
</code></pre>
<ul>
<li><strong>Partial is also useful in cases when a function needs to be passed as an argument because it enables us to set its arguments beforehand.</strong></li>
<li><strong>A few examples being: <code class="python hljs"><span class="hljs-string">'defaultdict(<func>)'</span></code>, <code class="python hljs"><span class="hljs-string">'iter(<func>, to_exc)'</span></code> and dataclass's <code class="python hljs"><span class="hljs-string">'field(default_factory=<func>)'</span></code>.</strong></li>
</ul>
<div><h3 id="nonlocal">Non-Local</h3><p><strong>If variable is being assigned to anywhere in the scope, it is regarded as a local variable, unless it is declared as a 'global' or a 'nonlocal'.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_counter</span><span class="hljs-params">()</span>:</span>
i = <span class="hljs-number">0</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">()</span>:</span>
<span class="hljs-keyword">nonlocal</span> i
i += <span class="hljs-number">1</span>
<span class="hljs-keyword">return</span> i
<span class="hljs-keyword">return</span> out
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>counter = get_counter()
<span class="hljs-meta">>>> </span>counter(), counter(), counter()
(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
</code></pre>
<div class="pagebreak"></div><div><h2 id="decorator"><a href="#decorator" name="decorator">#</a>Decorator</h2><ul>
<li><strong>A decorator takes a function, adds some functionality and returns it.</strong></li>
<li><strong>It can be any <a href="#callable">callable</a>, but is usually implemented as a function that returns a <a href="#closure">closure</a>.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-meta">@decorator_name</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">function_that_gets_passed_to_decorator</span><span class="hljs-params">()</span>:</span>
...
</code></pre></div>
<div><h3 id="debuggerexample">Debugger Example</h3><p><strong>Decorator that prints function's name every time the function is called.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> wraps
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">debug</span><span class="hljs-params">(func)</span>:</span>
<span class="hljs-meta"> @wraps(func)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(*args, **kwargs)</span>:</span>
print(func.__name__)
<span class="hljs-keyword">return</span> func(*args, **kwargs)
<span class="hljs-keyword">return</span> out
<span class="hljs-meta">@debug</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(x, y)</span>:</span>
<span class="hljs-keyword">return</span> x + y
</code></pre></div>
<ul>
<li><strong>Wraps is a helper decorator that copies the metadata of the passed function (func) to the function it is wrapping (out). Without it, <code class="python hljs"><span class="hljs-string">'add.__name__'</span></code> would return <code class="python hljs"><span class="hljs-string">'out'</span></code>.</strong></li>
</ul>
<div><h3 id="cache">Cache</h3><p><strong>Decorator that caches function's return values. All function's arguments must be hashable.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> cache
<span class="hljs-meta">@cache</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">fib</span><span class="hljs-params">(n)</span>:</span>
<span class="hljs-keyword">return</span> n <span class="hljs-keyword">if</span> n < <span class="hljs-number">2</span> <span class="hljs-keyword">else</span> fib(n-<span class="hljs-number">2</span>) + fib(n-<span class="hljs-number">1</span>)</code></pre></div>
<ul>
<li><strong>Potential problem with cache is that it can grow indefinitely. To clear stored values run <code class="python hljs"><span class="hljs-string">'<func>.cache_clear()'</span></code>, or use <code class="python hljs"><span class="hljs-string">'@lru_cache(maxsize=<int>)'</span></code> decorator instead.</strong></li>
<li><strong>CPython interpreter limits recursion depth to 3000 by default. To increase it run <code class="python hljs"><span class="hljs-string">'sys.setrecursionlimit(<int>)'</span></code>.</strong></li>
</ul>
<div><h3 id="parametrizeddecorator">Parametrized Decorator</h3><p><strong>A decorator that accepts arguments and returns a normal decorator that accepts a function.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> wraps
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">debug</span><span class="hljs-params">(print_result=<span class="hljs-keyword">False</span>)</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">decorator</span><span class="hljs-params">(func)</span>:</span>
<span class="hljs-meta"> @wraps(func)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(*args, **kwargs)</span>:</span>
result = func(*args, **kwargs)
print(func.__name__, result <span class="hljs-keyword">if</span> print_result <span class="hljs-keyword">else</span> <span class="hljs-string">''</span>)
<span class="hljs-keyword">return</span> result
<span class="hljs-keyword">return</span> out
<span class="hljs-keyword">return</span> decorator
<span class="hljs-meta">@debug(print_result=True)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(x, y)</span>:</span>
<span class="hljs-keyword">return</span> x + y
</code></pre></div>
<ul>
<li><strong>Using only <code class="python hljs"><span class="hljs-string">'@debug'</span></code> to decorate the add() function would not work here, because debug would then receive the add() function as a 'print_result' argument. Decorators can however manually check if the argument they received is a function and act accordingly.</strong></li>
</ul>
<div><h2 id="class"><a href="#class" name="class">#</a>Class</h2><p><strong>A template for creating user-defined objects.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClass</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self.a = a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> str(self.a)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__repr__</span><span class="hljs-params">(self)</span>:</span>
class_name = self.__class__.__name__
<span class="hljs-keyword">return</span> <span class="hljs-string">f'<span class="hljs-subst">{class_name}</span>(<span class="hljs-subst">{self.a!r}</span>)'</span>
<span class="hljs-meta"> @classmethod</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_class_name</span><span class="hljs-params">(cls)</span>:</span>
<span class="hljs-keyword">return</span> cls.__name__
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>obj = MyClass(<span class="hljs-number">1</span>)
<span class="hljs-meta">>>> </span>obj.a, str(obj), repr(obj)
(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>, <span class="hljs-string">'MyClass(1)'</span>)
</code></pre>
<ul>
<li><strong>Return value of str() should be readable and of repr() unambiguous.</strong></li>
<li><strong>If only repr() is defined, it will also be used for str().</strong></li>
<li><strong>Methods decorated with <code class="python hljs"><span class="hljs-string">'@staticmethod'</span></code> do not receive 'self' nor 'cls' as their first argument.</strong></li>
</ul>
<div><h4 id="expressionsthatcallthestrmethod">Expressions that call the str() method:</h4><pre><code class="python language-python hljs">print(<obj>)
<span class="hljs-string">f'<span class="hljs-subst">{<obj>}</span>'</span>
logging.warning(<obj>)
csv.writer(<file>).writerow([<obj>])
<span class="hljs-keyword">raise</span> Exception(<obj>)
</code></pre></div>
<div><h4 id="expressionsthatcallthereprmethod">Expressions that call the repr() method:</h4><pre><code class="python language-python hljs">print/str/repr([<obj>])
print/str/repr({<obj>: <obj>})
<span class="hljs-string">f'<span class="hljs-subst">{<obj>!r}</span>'</span>
Z = make_dataclass(<span class="hljs-string">'Z'</span>, [<span class="hljs-string">'a'</span>]); print/str/repr(Z(<obj>))
<span class="hljs-meta">>>> </span><obj>
</code></pre></div>
<div><h3 id="inheritance">Inheritance</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name)</span>:</span>
self.name = name
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Employee</span><span class="hljs-params">(Person)</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name, staff_num)</span>:</span>
super().__init__(name)
self.staff_num = staff_num
</code></pre></div>
<div><h4 id="multipleinheritance">Multiple inheritance:</h4><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">A</span>:</span> <span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">B</span>:</span> <span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">C</span><span class="hljs-params">(A, B)</span>:</span> <span class="hljs-keyword">pass</span>
</code></pre></div>
<p><strong>MRO determines the order in which parent classes are traversed when searching for a method or an attribute:</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>C.mro()
[<<span class="hljs-class"><span class="hljs-title">class</span> '<span class="hljs-title">C</span>'>, <<span class="hljs-title">class</span> '<span class="hljs-title">A</span>'>, <<span class="hljs-title">class</span> '<span class="hljs-title">B</span>'>, <<span class="hljs-title">class</span> '<span class="hljs-title">object</span>'>]
</span></code></pre>
<div><h3 id="typeannotations">Type Annotations</h3><ul>
<li><strong>They add type hints to variables, arguments and functions (<code class="python hljs"><span class="hljs-string">'def f() -> <type>:'</span></code>).</strong></li>
<li><strong>Hints are used by type checkers like <a href="https://pypi.org/project/mypy/">mypy</a>, data validation libraries such as <a href="https://pypi.org/project/pydantic/">Pydantic</a> and lately also by <a href="https://pypi.org/project/Cython/">Cython</a> compiler. However, they are not enforced by CPython interpreter.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> abc
<name>: <type> [| ...] [= <obj>]
<name>: list/set/abc.Iterable/abc.Sequence[<type>] [= <obj>]
<name>: dict/tuple[<type>, ...] [= <obj>]
</code></pre></div>
<div><h3 id="dataclass">Dataclass</h3><p><strong>Decorator that uses class variables to generate init(), repr() and eq() special methods.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> dataclasses <span class="hljs-keyword">import</span> dataclass, field, make_dataclass
<span class="hljs-meta">@dataclass(order=False, frozen=False)</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <<span class="hljs-title">class_name</span>>:</span>
<attr_name>: <type>
<attr_name>: <type> = <default_value>
<attr_name>: list/dict/set = field(default_factory=list/dict/set)
</code></pre></div>
<ul>
<li><strong>Objects can be made <a href="#sortable">sortable</a> with <code class="python hljs"><span class="hljs-string">'order=True'</span></code> and immutable with <code class="python hljs"><span class="hljs-string">'frozen=True'</span></code>.</strong></li>
<li><strong>For object to be <a href="#hashable">hashable</a>, all attributes must be hashable and 'frozen' must be True.</strong></li>
<li><strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">'<attr_name>: list = []'</span></code> would make a list that is shared among all instances. Its 'default_factory' argument can be any <a href="#callable">callable</a>.</strong></li>
<li><strong>For attributes of arbitrary type use <code class="python hljs"><span class="hljs-string">'typing.Any'</span></code>.</strong></li>
</ul>
<pre><code class="python language-python hljs">P = make_dataclass(<span class="hljs-string">'P'</span>, [<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>])
P = make_dataclass(<span class="hljs-string">'P'</span>, [(<span class="hljs-string">'x'</span>, float), (<span class="hljs-string">'y'</span>, float)])
P = make_dataclass(<span class="hljs-string">'P'</span>, [(<span class="hljs-string">'x'</span>, float, <span class="hljs-number">0</span>), (<span class="hljs-string">'y'</span>, float, <span class="hljs-number">0</span>)])
</code></pre>
<div><h3 id="property">Property</h3><p><strong>Pythonic way of implementing getters and setters.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
<span class="hljs-meta"> @property</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">name</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> <span class="hljs-string">' '</span>.join(self._name)
<span class="hljs-meta"> @name.setter</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">name</span><span class="hljs-params">(self, value)</span>:</span>
self._name = value.split()
</code></pre></div>
<pre><code class="python language-python hljs"><span class="hljs-meta">>>> </span>person = Person()
<span class="hljs-meta">>>> </span>person.name = <span class="hljs-string">'\t Guido van Rossum \n'</span>
<span class="hljs-meta">>>> </span>person.name
<span class="hljs-string">'Guido van Rossum'</span>
</code></pre>
<div><h3 id="slots">Slots</h3><p><strong>Mechanism that restricts objects to attributes listed in 'slots', reduces their memory footprint.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClassWithSlots</span>:</span>
__slots__ = [<span class="hljs-string">'a'</span>]
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
self.a = <span class="hljs-number">1</span>
</code></pre></div>
<div><h3 id="copy">Copy</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> copy <span class="hljs-keyword">import</span> copy, deepcopy
<object> = copy/deepcopy(<object>)
</code></pre></div>
<div><h2 id="ducktypes"><a href="#ducktypes" name="ducktypes">#</a>Duck Types</h2><p><strong>A duck type is an implicit type that prescribes a set of special methods. Any object that has those methods defined is considered a member of that duck type.</strong></p><div><h3 id="comparable">Comparable</h3><ul>
<li><strong>If eq() method is not overridden, it returns <code class="python hljs"><span class="hljs-string">'id(self) == id(other)'</span></code>, which is the same as <code class="python hljs"><span class="hljs-string">'self is other'</span></code>.</strong></li>
<li><strong>That means all user-defined objects compare not equal by default.</strong></li>
<li><strong>Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted. False is returned if both return NotImplemented.</strong></li>
<li><strong>Ne() automatically works on any object that has eq() defined.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyComparable</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self.a = a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__eq__</span><span class="hljs-params">(self, other)</span>:</span>
<span class="hljs-keyword">if</span> isinstance(other, type(self)):
<span class="hljs-keyword">return</span> self.a == other.a
<span class="hljs-keyword">return</span> <span class="hljs-built_in">NotImplemented</span>
</code></pre></div></div>
<div><h3 id="hashable">Hashable</h3><ul>
<li><strong>Hashable object needs both hash() and eq() methods and its hash value should never change.</strong></li>
<li><strong>Hashable objects that compare equal must have the same hash value, meaning default hash() that returns <code class="python hljs"><span class="hljs-string">'id(self)'</span></code> will not do.</strong></li>
<li><strong>That is why Python automatically makes classes unhashable if you only implement eq().</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyHashable</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self._a = a
<span class="hljs-meta"> @property</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">a</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> self._a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__eq__</span><span class="hljs-params">(self, other)</span>:</span>
<span class="hljs-keyword">if</span> isinstance(other, type(self)):
<span class="hljs-keyword">return</span> self.a == other.a
<span class="hljs-keyword">return</span> <span class="hljs-built_in">NotImplemented</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__hash__</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> hash(self.a)
</code></pre></div>
<div><h3 id="sortable">Sortable</h3><ul>
<li><strong>With 'total_ordering' decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods and the rest will be automatically generated.</strong></li>
<li><strong>Functions sorted() and min() only require lt() method, while max() only requires gt(). However, it is best to define them all so that confusion doesn't arise in other contexts.</strong></li>
<li><strong>When two lists, strings or dataclasses are compared, their values get compared in order until a pair of unequal values is found. The comparison of this two values is then returned. The shorter sequence is considered smaller in case of all values being equal.</strong></li>
<li><strong>To sort collection of strings in proper alphabetical order pass <code class="python hljs"><span class="hljs-string">'key=locale.strxfrm'</span></code> to sorted() after running <code class="python hljs"><span class="hljs-string">'locale.setlocale(locale.LC_COLLATE, "en_US.UTF-8")'</span></code>.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> total_ordering
<span class="hljs-meta">@total_ordering</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MySortable</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
self.a = a
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__eq__</span><span class="hljs-params">(self, other)</span>:</span>
<span class="hljs-keyword">if</span> isinstance(other, type(self)):
<span class="hljs-keyword">return</span> self.a == other.a
<span class="hljs-keyword">return</span> <span class="hljs-built_in">NotImplemented</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__lt__</span><span class="hljs-params">(self, other)</span>:</span>
<span class="hljs-keyword">if</span> isinstance(other, type(self)):
<span class="hljs-keyword">return</span> self.a < other.a
<span class="hljs-keyword">return</span> <span class="hljs-built_in">NotImplemented</span>
</code></pre></div>
<div><h3 id="iterator-1">Iterator</h3><ul>
<li><strong>Any object that has methods next() and iter() is an iterator.</strong></li>
<li><strong>Next() should return next item or raise StopIteration exception.</strong></li>
<li><strong>Iter() should return an iterator of remaining items, i.e. 'self'.</strong></li>
<li><strong>Any object that has iter() method can be used in a for loop.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Counter</span>:</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
self.i = <span class="hljs-number">0</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__next__</span><span class="hljs-params">(self)</span>:</span>
self.i += <span class="hljs-number">1</span>
<span class="hljs-keyword">return</span> self.i
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__iter__</span><span class="hljs-params">(self)</span>:</span>
<span class="hljs-keyword">return</span> self