-
Notifications
You must be signed in to change notification settings - Fork 10
Expand file tree
/
Copy pathlibrary.html
More file actions
1031 lines (970 loc) · 86.2 KB
/
Copy pathlibrary.html
File metadata and controls
1031 lines (970 loc) · 86.2 KB
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 lang="fa" data-content_root="../">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />
<meta property="og:title" content="Library and Extension FAQ" />
<meta property="og:type" content="website" />
<meta property="og:url" content="https://docs.python.org/3/faq/library.html" />
<meta property="og:site_name" content="Python documentation" />
<meta property="og:description" content="محتوا: Library and Extension FAQ- General Library Questions- How do I find a module or application to perform task X?, Where is the math.py (socket.py, regex.py, etc.) source file?, How do I make a..." />
<meta property="og:image" content="_static/og-image.png" />
<meta property="og:image:alt" content="Python documentation" />
<meta name="description" content="محتوا: Library and Extension FAQ- General Library Questions- How do I find a module or application to perform task X?, Where is the math.py (socket.py, regex.py, etc.) source file?, How do I make a..." />
<meta name="theme-color" content="#3776ab">
<meta property="og:image:width" content="200">
<meta property="og:image:height" content="200">
<title>Library and Extension FAQ — مستندات Python3.14.6</title><meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=b86133f3" />
<link rel="stylesheet" type="text/css" href="../_static/classic.css?v=234b1a7c" />
<link rel="stylesheet" type="text/css" href="../_static/pydoctheme.css?v=4365c8fe" />
<link id="pygments_dark_css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css" href="../_static/pygments_dark.css?v=0fc419ee" />
<script src="../_static/documentation_options.js?v=e254dbbb"></script>
<script src="../_static/doctools.js?v=9bcbadda"></script>
<script src="../_static/sphinx_highlight.js?v=dc90522c"></script>
<script src="../_static/translations.js?v=5df48d09"></script>
<script src="../_static/sidebar.js"></script>
<link rel="search" type="application/opensearchdescription+xml"
title="جستجو در مستندات Python3.14.6"
href="../_static/opensearch.xml"/>
<link rel="author" title="درباره این مستندات" href="../about.html" />
<link rel="index" title="فهرست" href="../genindex.html" />
<link rel="search" title="جستجو" href="../search.html" />
<link rel="copyright" title="حق چاپ" href="../copyright.html" />
<link rel="next" title="Extending/Embedding FAQ" href="extending.html" />
<link rel="prev" title="Design and History FAQ" href="design.html" />
<link rel="canonical" href="https://docs.python.org/3/faq/library.html">
<style>
@media only screen {
table.full-width-table {
width: 100%;
}
}
</style>
<link rel="stylesheet" href="../_static/pydoctheme_dark.css" media="(prefers-color-scheme: dark)" id="pydoctheme_dark_css">
<link rel="shortcut icon" type="image/png" href="../_static/py.svg">
<script type="text/javascript" src="../_static/copybutton.js"></script>
<script type="text/javascript" src="../_static/menu.js"></script>
<script type="text/javascript" src="../_static/search-focus.js"></script>
<script type="text/javascript" src="../_static/themetoggle.js"></script>
<script type="text/javascript" src="../_static/rtd_switcher.js"></script>
<meta name="readthedocs-addons-api-version" content="1">
</head>
<body>
<div class="mobile-nav">
<input type="checkbox" id="menuToggler" class="toggler__input" aria-controls="navigation"
aria-pressed="false" aria-expanded="false" role="button" aria-label="Menu">
<nav class="nav-content" role="navigation">
<label for="menuToggler" class="toggler__label">
<span></span>
</label>
<span class="nav-items-wrapper">
<a href="https://www.python.org/" class="nav-logo">
<img src="../_static/py.svg" alt="Python logo">
</a>
<span class="version_switcher_placeholder"></span>
<form role="search" class="search" action="../search.html" method="get">
<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" class="search-icon">
<path fill-rule="nonzero" fill="currentColor" d="M15.5 14h-.79l-.28-.27a6.5 6.5 0 001.48-5.34c-.47-2.78-2.79-5-5.59-5.34a6.505 6.505 0 00-7.27 7.27c.34 2.8 2.56 5.12 5.34 5.59a6.5 6.5 0 005.34-1.48l.27.28v.79l4.25 4.25c.41.41 1.08.41 1.49 0 .41-.41.41-1.08 0-1.49L15.5 14zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"></path>
</svg>
<input placeholder="جستجو سریع" aria-label="جستجو سریع" type="search" name="q">
<input type="submit" value="برو">
</form>
</span>
</nav>
<div class="menu-wrapper">
<nav class="menu" role="navigation" aria-label="main navigation">
<div class="language_switcher_placeholder"></div>
<label class="theme-selector-label">
Theme
<select class="theme-selector" oninput="activateTheme(this.value)">
<option value="auto" selected>Auto</option>
<option value="light">Light</option>
<option value="dark">Dark</option>
</select>
</label>
<div>
<h3><a href="../contents.html">فهرست عناوین</a></h3>
<ul>
<li><a class="reference internal" href="#">Library and Extension FAQ</a><ul>
<li><a class="reference internal" href="#general-library-questions">General Library Questions</a></li>
<li><a class="reference internal" href="#common-tasks">Common tasks</a></li>
<li><a class="reference internal" href="#threads">Threads</a></li>
<li><a class="reference internal" href="#input-and-output">Input and Output</a></li>
<li><a class="reference internal" href="#network-internet-programming">Network/Internet Programming</a></li>
<li><a class="reference internal" href="#databases">Databases</a></li>
<li><a class="reference internal" href="#mathematics-and-numerics">Mathematics and Numerics</a></li>
</ul>
</li>
</ul>
</div>
<div>
<h4>موضوع قبلی</h4>
<p class="topless"><a href="design.html"
title="فصل قبلی">Design and History FAQ</a></p>
</div>
<div>
<h4>موضوع بعدی</h4>
<p class="topless"><a href="extending.html"
title="فصل بعدی">Extending/Embedding FAQ</a></p>
</div>
<script>
document.addEventListener('DOMContentLoaded', () => {
const title = document.querySelector('meta[property="og:title"]').content;
const elements = document.querySelectorAll('.improvepage');
const pageurl = window.location.href.split('?')[0];
elements.forEach(element => {
const url = new URL(element.href.split('?')[0].replace("-nojs", ""));
url.searchParams.set('pagetitle', title);
url.searchParams.set('pageurl', pageurl);
url.searchParams.set('pagesource', "faq/library.rst");
element.href = url.toString();
});
});
</script>
<div role="note" aria-label="source link">
<h3>این صفحه</h3>
<ul class="this-page-menu">
<li><a href="../bugs.html">گزارش یک اشکال</a></li>
<li><a class="improvepage" href="../improve-page-nojs.html">بهبود این صفحه</a></li>
<li>
<a href="https://github.com/python/cpython/blob/main/Doc/faq/library.rst?plain=1"
rel="nofollow">نمایش منبع
</a>
</li>
<li>
<a href="https://github.com/python/python-docs-fa/blob/3.14/faq/library.po?plain=1"
rel="nofollow">نمایش منبع ترجمه</a>
</li>
</ul>
</div>
</nav>
</div>
</div>
<div class="related" role="navigation" aria-label="Related">
<h3>ناوبری</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="فهرست کلی"
accesskey="I">فهرست</a></li>
<li class="right" >
<a href="../py-modindex.html" title="نمایه ی ماژول های پایتون"
>ماژول ها</a> |</li>
<li class="right" >
<a href="extending.html" title="Extending/Embedding FAQ"
accesskey="N">بعدی</a> |</li>
<li class="right" >
<a href="design.html" title="Design and History FAQ"
accesskey="P">قبلی</a> |</li>
<li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li class="switchers">
<div class="language_switcher_placeholder"></div>
<div class="version_switcher_placeholder"></div>
</li>
<li>
</li>
<li id="cpython-language-and-version">
<a href="../index.html">3.14.6 Documentation</a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" accesskey="U">Python Frequently Asked Questions</a> »</li>
<li class="nav-item nav-item-this"><a href="">Library and Extension FAQ</a></li>
<li class="right">
<div class="inline-search" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="جستجو سریع" aria-label="جستجو سریع" type="search" name="q" id="search-box">
<input type="submit" value="برو">
</form>
</div>
|
</li>
<li class="right">
<label class="theme-selector-label">
Theme
<select class="theme-selector" oninput="activateTheme(this.value)">
<option value="auto" selected>Auto</option>
<option value="light">Light</option>
<option value="dark">Dark</option>
</select>
</label> |</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<section id="library-and-extension-faq">
<h1><a class="toc-backref" href="#id2" role="doc-backlink">Library and Extension FAQ</a><a class="headerlink" href="#library-and-extension-faq" title="Link to this heading">¶</a></h1>
<nav class="contents" id="id1">
<p class="topic-title">محتوا</p>
<ul class="simple">
<li><p><a class="reference internal" href="#library-and-extension-faq" id="id2">Library and Extension FAQ</a></p>
<ul>
<li><p><a class="reference internal" href="#general-library-questions" id="id3">General Library Questions</a></p>
<ul>
<li><p><a class="reference internal" href="#how-do-i-find-a-module-or-application-to-perform-task-x" id="id4">How do I find a module or application to perform task X?</a></p></li>
<li><p><a class="reference internal" href="#where-is-the-math-py-socket-py-regex-py-etc-source-file" id="id5">Where is the math.py (socket.py, regex.py, etc.) source file?</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-make-a-python-script-executable-on-unix" id="id6">How do I make a Python script executable on Unix?</a></p></li>
<li><p><a class="reference internal" href="#is-there-a-curses-termcap-package-for-python" id="id7">Is there a curses/termcap package for Python?</a></p></li>
<li><p><a class="reference internal" href="#is-there-an-equivalent-to-c-s-onexit-in-python" id="id8">Is there an equivalent to C's onexit() in Python?</a></p></li>
<li><p><a class="reference internal" href="#why-don-t-my-signal-handlers-work" id="id9">Why don't my signal handlers work?</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#common-tasks" id="id10">Common tasks</a></p>
<ul>
<li><p><a class="reference internal" href="#how-do-i-test-a-python-program-or-component" id="id11">How do I test a Python program or component?</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-create-documentation-from-doc-strings" id="id12">How do I create documentation from doc strings?</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-get-a-single-keypress-at-a-time" id="id13">How do I get a single keypress at a time?</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#threads" id="id14">Threads</a></p>
<ul>
<li><p><a class="reference internal" href="#how-do-i-program-using-threads" id="id15">How do I program using threads?</a></p></li>
<li><p><a class="reference internal" href="#none-of-my-threads-seem-to-run-why" id="id16">None of my threads seem to run: why?</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-parcel-out-work-among-a-bunch-of-worker-threads" id="id17">How do I parcel out work among a bunch of worker threads?</a></p></li>
<li><p><a class="reference internal" href="#what-kinds-of-global-value-mutation-are-thread-safe" id="id18">What kinds of global value mutation are thread-safe?</a></p></li>
<li><p><a class="reference internal" href="#can-t-we-get-rid-of-the-global-interpreter-lock" id="id19">Can't we get rid of the Global Interpreter Lock?</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#input-and-output" id="id20">Input and Output</a></p>
<ul>
<li><p><a class="reference internal" href="#how-do-i-delete-a-file-and-other-file-questions" id="id21">How do I delete a file? (And other file questions...)</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-copy-a-file" id="id22">How do I copy a file?</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-read-or-write-binary-data" id="id23">How do I read (or write) binary data?</a></p></li>
<li><p><a class="reference internal" href="#i-can-t-seem-to-use-os-read-on-a-pipe-created-with-os-popen-why" id="id24">I can't seem to use os.read() on a pipe created with os.popen(); why?</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-access-the-serial-rs232-port" id="id25">How do I access the serial (RS232) port?</a></p></li>
<li><p><a class="reference internal" href="#why-doesn-t-closing-sys-stdout-stdin-stderr-really-close-it" id="id26">Why doesn't closing sys.stdout (stdin, stderr) really close it?</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#network-internet-programming" id="id27">Network/Internet Programming</a></p>
<ul>
<li><p><a class="reference internal" href="#what-www-tools-are-there-for-python" id="id28">What WWW tools are there for Python?</a></p></li>
<li><p><a class="reference internal" href="#what-module-should-i-use-to-help-with-generating-html" id="id29">What module should I use to help with generating HTML?</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-send-mail-from-a-python-script" id="id30">How do I send mail from a Python script?</a></p></li>
<li><p><a class="reference internal" href="#how-do-i-avoid-blocking-in-the-connect-method-of-a-socket" id="id31">How do I avoid blocking in the connect() method of a socket?</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#databases" id="id32">Databases</a></p>
<ul>
<li><p><a class="reference internal" href="#are-there-any-interfaces-to-database-packages-in-python" id="id33">Are there any interfaces to database packages in Python?</a></p></li>
<li><p><a class="reference internal" href="#how-do-you-implement-persistent-objects-in-python" id="id34">How do you implement persistent objects in Python?</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#mathematics-and-numerics" id="id35">Mathematics and Numerics</a></p>
<ul>
<li><p><a class="reference internal" href="#how-do-i-generate-random-numbers-in-python" id="id36">How do I generate random numbers in Python?</a></p></li>
</ul>
</li>
</ul>
</li>
</ul>
</nav>
<section id="general-library-questions">
<h2><a class="toc-backref" href="#id3" role="doc-backlink">General Library Questions</a><a class="headerlink" href="#general-library-questions" title="Link to this heading">¶</a></h2>
<section id="how-do-i-find-a-module-or-application-to-perform-task-x">
<h3><a class="toc-backref" href="#id4" role="doc-backlink">How do I find a module or application to perform task X?</a><a class="headerlink" href="#how-do-i-find-a-module-or-application-to-perform-task-x" title="Link to this heading">¶</a></h3>
<p>Check <a class="reference internal" href="../library/index.html#library-index"><span class="std std-ref">the Library Reference</span></a> to see if there's a relevant
standard library module. (Eventually you'll learn what's in the standard
library and will be able to skip this step.)</p>
<p>For third-party packages, search the <a class="reference external" href="https://pypi.org">Python Package Index</a> or try <a class="reference external" href="https://www.google.com">Google</a> or
another web search engine. Searching for "Python" plus a keyword or two for
your topic of interest will usually find something helpful.</p>
</section>
<section id="where-is-the-math-py-socket-py-regex-py-etc-source-file">
<h3><a class="toc-backref" href="#id5" role="doc-backlink">Where is the math.py (socket.py, regex.py, etc.) source file?</a><a class="headerlink" href="#where-is-the-math-py-socket-py-regex-py-etc-source-file" title="Link to this heading">¶</a></h3>
<p>If you can't find a source file for a module it may be a built-in or
dynamically loaded module implemented in C, C++ or other compiled language.
In this case you may not have the source file or it may be something like
<code class="file docutils literal notranslate"><span class="pre">mathmodule.c</span></code>, somewhere in a C source directory (not on the Python Path).</p>
<p>There are (at least) three kinds of modules in Python:</p>
<ol class="arabic">
<li><p>modules written in Python (.py);</p></li>
<li><p>modules written in C and dynamically loaded (.dll, .pyd, .so, .sl, etc);</p></li>
<li><p>modules written in C and linked with the interpreter; to get a list of these,
type:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">sys</span>
<span class="nb">print</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">builtin_module_names</span><span class="p">)</span>
</pre></div>
</div>
</li>
</ol>
</section>
<section id="how-do-i-make-a-python-script-executable-on-unix">
<h3><a class="toc-backref" href="#id6" role="doc-backlink">How do I make a Python script executable on Unix?</a><a class="headerlink" href="#how-do-i-make-a-python-script-executable-on-unix" title="Link to this heading">¶</a></h3>
<p>You need to do two things: the script file's mode must be executable and the
first line must begin with <code class="docutils literal notranslate"><span class="pre">#!</span></code> followed by the path of the Python
interpreter.</p>
<p>The first is done by executing <code class="docutils literal notranslate"><span class="pre">chmod</span> <span class="pre">+x</span> <span class="pre">scriptfile</span></code> or perhaps <code class="docutils literal notranslate"><span class="pre">chmod</span> <span class="pre">755</span>
<span class="pre">scriptfile</span></code>.</p>
<p>The second can be done in a number of ways. The most straightforward way is to
write</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="ch">#!/usr/local/bin/python</span>
</pre></div>
</div>
<p>as the very first line of your file, using the pathname for where the Python
interpreter is installed on your platform.</p>
<p>If you would like the script to be independent of where the Python interpreter
lives, you can use the <strong class="program">env</strong> program. Almost all Unix variants support
the following, assuming the Python interpreter is in a directory on the user's
<span class="target" id="index-0"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python</span>
</pre></div>
</div>
<p><em>Don't</em> do this for CGI scripts. The <span class="target" id="index-1"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code> variable for CGI scripts is
often very minimal, so you need to use the actual absolute pathname of the
interpreter.</p>
<p>Occasionally, a user's environment is so full that the <strong class="program">/usr/bin/env</strong>
program fails; or there's no env program at all. In that case, you can try the
following hack (due to Alex Rezinsky):</p>
<div class="highlight-sh notranslate"><div class="highlight"><pre><span></span><span class="ch">#! /bin/sh</span>
<span class="s2">""":"</span>
<span class="nb">exec</span><span class="w"> </span>python<span class="w"> </span><span class="nv">$0</span><span class="w"> </span><span class="si">${</span><span class="nv">1</span><span class="p">+</span><span class="s2">"</span><span class="nv">$@</span><span class="s2">"</span><span class="si">}</span>
<span class="s2">"""</span>
</pre></div>
</div>
<p>The minor disadvantage is that this defines the script's __doc__ string.
However, you can fix that by adding</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="vm">__doc__</span> <span class="o">=</span> <span class="s2">"""...Whatever..."""</span>
</pre></div>
</div>
</section>
<section id="is-there-a-curses-termcap-package-for-python">
<h3><a class="toc-backref" href="#id7" role="doc-backlink">Is there a curses/termcap package for Python?</a><a class="headerlink" href="#is-there-a-curses-termcap-package-for-python" title="Link to this heading">¶</a></h3>
<p>For Unix variants: The standard Python source distribution comes with a curses
module in the <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.14/Modules">Modules</a> subdirectory, though it's not compiled by default.
(Note that this is not available in the Windows distribution -- there is no
curses module for Windows.)</p>
<p>The <a class="reference internal" href="../library/curses.html#module-curses" title="curses: An interface to the curses library, providing portable terminal handling."><code class="xref py py-mod docutils literal notranslate"><span class="pre">curses</span></code></a> module supports basic curses features as well as many additional
functions from ncurses and SYSV curses such as colour, alternative character set
support, pads, and mouse support. This means the module isn't compatible with
operating systems that only have BSD curses, but there don't seem to be any
currently maintained OSes that fall into this category.</p>
</section>
<section id="is-there-an-equivalent-to-c-s-onexit-in-python">
<h3><a class="toc-backref" href="#id8" role="doc-backlink">Is there an equivalent to C's onexit() in Python?</a><a class="headerlink" href="#is-there-an-equivalent-to-c-s-onexit-in-python" title="Link to this heading">¶</a></h3>
<p>The <a class="reference internal" href="../library/atexit.html#module-atexit" title="atexit: Register and execute cleanup functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code></a> module provides a register function that is similar to C's
<code class="xref c c-func docutils literal notranslate"><span class="pre">onexit()</span></code>.</p>
</section>
<section id="why-don-t-my-signal-handlers-work">
<h3><a class="toc-backref" href="#id9" role="doc-backlink">Why don't my signal handlers work?</a><a class="headerlink" href="#why-don-t-my-signal-handlers-work" title="Link to this heading">¶</a></h3>
<p>The most common problem is that the signal handler is declared with the wrong
argument list. It is called as</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">handler</span><span class="p">(</span><span class="n">signum</span><span class="p">,</span> <span class="n">frame</span><span class="p">)</span>
</pre></div>
</div>
<p>so it should be declared with two parameters:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">handler</span><span class="p">(</span><span class="n">signum</span><span class="p">,</span> <span class="n">frame</span><span class="p">):</span>
<span class="o">...</span>
</pre></div>
</div>
</section>
</section>
<section id="common-tasks">
<h2><a class="toc-backref" href="#id10" role="doc-backlink">Common tasks</a><a class="headerlink" href="#common-tasks" title="Link to this heading">¶</a></h2>
<section id="how-do-i-test-a-python-program-or-component">
<h3><a class="toc-backref" href="#id11" role="doc-backlink">How do I test a Python program or component?</a><a class="headerlink" href="#how-do-i-test-a-python-program-or-component" title="Link to this heading">¶</a></h3>
<p>Python comes with two testing frameworks. The <a class="reference internal" href="../library/doctest.html#module-doctest" title="doctest: Test pieces of code within docstrings."><code class="xref py py-mod docutils literal notranslate"><span class="pre">doctest</span></code></a> module finds
examples in the docstrings for a module and runs them, comparing the output with
the expected output given in the docstring.</p>
<p>The <a class="reference internal" href="../library/unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><code class="xref py py-mod docutils literal notranslate"><span class="pre">unittest</span></code></a> module is a fancier testing framework modelled on Java and
Smalltalk testing frameworks.</p>
<p>To make testing easier, you should use good modular design in your program.
Your program should have almost all functionality
encapsulated in either functions or class methods -- and this sometimes has the
surprising and delightful effect of making the program run faster (because local
variable accesses are faster than global accesses). Furthermore the program
should avoid depending on mutating global variables, since this makes testing
much more difficult to do.</p>
<p>The "global main logic" of your program may be as simple as</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s2">"__main__"</span><span class="p">:</span>
<span class="n">main_logic</span><span class="p">()</span>
</pre></div>
</div>
<p>at the bottom of the main module of your program.</p>
<p>Once your program is organized as a tractable collection of function and class
behaviours, you should write test functions that exercise the behaviours. A
test suite that automates a sequence of tests can be associated with each module.
This sounds like a lot of work, but since Python is so terse and flexible it's
surprisingly easy. You can make coding much more pleasant and fun by writing
your test functions in parallel with the "production code", since this makes it
easy to find bugs and even design flaws earlier.</p>
<p>"Support modules" that are not intended to be the main module of a program may
include a self-test of the module.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s2">"__main__"</span><span class="p">:</span>
<span class="n">self_test</span><span class="p">()</span>
</pre></div>
</div>
<p>Even programs that interact with complex external interfaces may be tested when
the external interfaces are unavailable by using "fake" interfaces implemented
in Python.</p>
</section>
<section id="how-do-i-create-documentation-from-doc-strings">
<h3><a class="toc-backref" href="#id12" role="doc-backlink">How do I create documentation from doc strings?</a><a class="headerlink" href="#how-do-i-create-documentation-from-doc-strings" title="Link to this heading">¶</a></h3>
<p>The <a class="reference internal" href="../library/pydoc.html#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pydoc</span></code></a> module can create HTML from the doc strings in your Python
source code. An alternative for creating API documentation purely from
docstrings is <a class="reference external" href="https://epydoc.sourceforge.net/">epydoc</a>. <a class="reference external" href="https://www.sphinx-doc.org">Sphinx</a> can also include docstring content.</p>
</section>
<section id="how-do-i-get-a-single-keypress-at-a-time">
<h3><a class="toc-backref" href="#id13" role="doc-backlink">How do I get a single keypress at a time?</a><a class="headerlink" href="#how-do-i-get-a-single-keypress-at-a-time" title="Link to this heading">¶</a></h3>
<p>For Unix variants there are several solutions. It's straightforward to do this
using curses, but curses is a fairly large module to learn.</p>
</section>
</section>
<section id="threads">
<h2><a class="toc-backref" href="#id14" role="doc-backlink">Threads</a><a class="headerlink" href="#threads" title="Link to this heading">¶</a></h2>
<section id="how-do-i-program-using-threads">
<h3><a class="toc-backref" href="#id15" role="doc-backlink">How do I program using threads?</a><a class="headerlink" href="#how-do-i-program-using-threads" title="Link to this heading">¶</a></h3>
<p>Be sure to use the <a class="reference internal" href="../library/threading.html#module-threading" title="threading: Thread-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a> module and not the <a class="reference internal" href="../library/_thread.html#module-_thread" title="_thread: Low-level threading API."><code class="xref py py-mod docutils literal notranslate"><span class="pre">_thread</span></code></a> module.
The <code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code> module builds convenient abstractions on top of the
low-level primitives provided by the <code class="xref py py-mod docutils literal notranslate"><span class="pre">_thread</span></code> module.</p>
</section>
<section id="none-of-my-threads-seem-to-run-why">
<h3><a class="toc-backref" href="#id16" role="doc-backlink">None of my threads seem to run: why?</a><a class="headerlink" href="#none-of-my-threads-seem-to-run-why" title="Link to this heading">¶</a></h3>
<p>As soon as the main thread exits, all threads are killed. Your main thread is
running too quickly, giving the threads no time to do any work.</p>
<p>A simple fix is to add a sleep to the end of the program that's long enough for
all the threads to finish:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">threading</span><span class="o">,</span><span class="w"> </span><span class="nn">time</span>
<span class="k">def</span><span class="w"> </span><span class="nf">thread_task</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">n</span><span class="p">):</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">n</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">i</span><span class="p">)</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="n">T</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">Thread</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">thread_task</span><span class="p">,</span> <span class="n">args</span><span class="o">=</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">i</span><span class="p">),</span> <span class="n">i</span><span class="p">))</span>
<span class="n">T</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span> <span class="c1"># <---------------------------!</span>
</pre></div>
</div>
<p>But now (on many platforms) the threads don't run in parallel, but appear to run
sequentially, one at a time! The reason is that the OS thread scheduler doesn't
start a new thread until the previous thread is blocked.</p>
<p>A simple fix is to add a tiny sleep to the start of the run function:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">thread_task</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">n</span><span class="p">):</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mf">0.001</span><span class="p">)</span> <span class="c1"># <--------------------!</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">n</span><span class="p">):</span>
<span class="nb">print</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">i</span><span class="p">)</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="n">T</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">Thread</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">thread_task</span><span class="p">,</span> <span class="n">args</span><span class="o">=</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">i</span><span class="p">),</span> <span class="n">i</span><span class="p">))</span>
<span class="n">T</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span>
</pre></div>
</div>
<p>Instead of trying to guess a good delay value for <a class="reference internal" href="../library/time.html#time.sleep" title="time.sleep"><code class="xref py py-func docutils literal notranslate"><span class="pre">time.sleep()</span></code></a>,
it's better to use some kind of semaphore mechanism. One idea is to use the
<a class="reference internal" href="../library/queue.html#module-queue" title="queue: A synchronized queue class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code></a> module to create a queue object, let each thread append a token to
the queue when it finishes, and let the main thread read as many tokens from the
queue as there are threads.</p>
</section>
<section id="how-do-i-parcel-out-work-among-a-bunch-of-worker-threads">
<h3><a class="toc-backref" href="#id17" role="doc-backlink">How do I parcel out work among a bunch of worker threads?</a><a class="headerlink" href="#how-do-i-parcel-out-work-among-a-bunch-of-worker-threads" title="Link to this heading">¶</a></h3>
<p>The easiest way is to use the <a class="reference internal" href="../library/concurrent.futures.html#module-concurrent.futures" title="concurrent.futures: Execute computations concurrently using threads or processes."><code class="xref py py-mod docutils literal notranslate"><span class="pre">concurrent.futures</span></code></a> module,
especially the <a class="reference internal" href="../library/concurrent.futures.html#concurrent.futures.ThreadPoolExecutor" title="concurrent.futures.ThreadPoolExecutor"><code class="xref py py-mod docutils literal notranslate"><span class="pre">ThreadPoolExecutor</span></code></a> class.</p>
<p>Or, if you want fine control over the dispatching algorithm, you can write
your own logic manually. Use the <a class="reference internal" href="../library/queue.html#module-queue" title="queue: A synchronized queue class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code></a> module to create a queue
containing a list of jobs. The <a class="reference internal" href="../library/queue.html#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> class maintains a
list of objects and has a <code class="docutils literal notranslate"><span class="pre">.put(obj)</span></code> method that adds items to the queue and
a <code class="docutils literal notranslate"><span class="pre">.get()</span></code> method to return them. The class will take care of the locking
necessary to ensure that each job is handed out exactly once.</p>
<p>Here's a trivial example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">threading</span><span class="o">,</span><span class="w"> </span><span class="nn">queue</span><span class="o">,</span><span class="w"> </span><span class="nn">time</span>
<span class="c1"># The worker thread gets jobs off the queue. When the queue is empty, it</span>
<span class="c1"># assumes there will be no more work and exits.</span>
<span class="c1"># (Realistically workers will run until terminated.)</span>
<span class="k">def</span><span class="w"> </span><span class="nf">worker</span><span class="p">():</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Running worker'</span><span class="p">)</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mf">0.1</span><span class="p">)</span>
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">arg</span> <span class="o">=</span> <span class="n">q</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">block</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
<span class="k">except</span> <span class="n">queue</span><span class="o">.</span><span class="n">Empty</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Worker'</span><span class="p">,</span> <span class="n">threading</span><span class="o">.</span><span class="n">current_thread</span><span class="p">(),</span> <span class="n">end</span><span class="o">=</span><span class="s1">' '</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'queue empty'</span><span class="p">)</span>
<span class="k">break</span>
<span class="k">else</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Worker'</span><span class="p">,</span> <span class="n">threading</span><span class="o">.</span><span class="n">current_thread</span><span class="p">(),</span> <span class="n">end</span><span class="o">=</span><span class="s1">' '</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'running with argument'</span><span class="p">,</span> <span class="n">arg</span><span class="p">)</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mf">0.5</span><span class="p">)</span>
<span class="c1"># Create queue</span>
<span class="n">q</span> <span class="o">=</span> <span class="n">queue</span><span class="o">.</span><span class="n">Queue</span><span class="p">()</span>
<span class="c1"># Start a pool of 5 workers</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">):</span>
<span class="n">t</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">Thread</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">worker</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s1">'worker </span><span class="si">%i</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="p">))</span>
<span class="n">t</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="c1"># Begin adding work to the queue</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">50</span><span class="p">):</span>
<span class="n">q</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
<span class="c1"># Give threads time to run</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Main thread sleeping'</span><span class="p">)</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
</pre></div>
</div>
<p>When run, this will produce the following output:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>Running worker
Running worker
Running worker
Running worker
Running worker
Main thread sleeping
Worker <Thread(worker 1, started 130283832797456)> running with argument 0
Worker <Thread(worker 2, started 130283824404752)> running with argument 1
Worker <Thread(worker 3, started 130283816012048)> running with argument 2
Worker <Thread(worker 4, started 130283807619344)> running with argument 3
Worker <Thread(worker 5, started 130283799226640)> running with argument 4
Worker <Thread(worker 1, started 130283832797456)> running with argument 5
...
</pre></div>
</div>
<p>Consult the module's documentation for more details; the <a class="reference internal" href="../library/queue.html#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a>
class provides a featureful interface.</p>
</section>
<section id="what-kinds-of-global-value-mutation-are-thread-safe">
<h3><a class="toc-backref" href="#id18" role="doc-backlink">What kinds of global value mutation are thread-safe?</a><a class="headerlink" href="#what-kinds-of-global-value-mutation-are-thread-safe" title="Link to this heading">¶</a></h3>
<p>A <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">global interpreter lock</span></a> (GIL) is used internally to ensure that only one
thread runs in the Python VM at a time. In general, Python offers to switch
among threads only between bytecode instructions; how frequently it switches can
be set via <a class="reference internal" href="../library/sys.html#sys.setswitchinterval" title="sys.setswitchinterval"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.setswitchinterval()</span></code></a>. Each bytecode instruction and
therefore all the C implementation code reached from each instruction is
therefore atomic from the point of view of a Python program.</p>
<p>In theory, this means an exact accounting requires an exact understanding of the
PVM bytecode implementation. In practice, it means that operations on shared
variables of built-in data types (ints, lists, dicts, etc) that "look atomic"
really are.</p>
<p>For example, the following operations are all atomic (L, L1, L2 are lists, D,
D1, D2 are dicts, x, y are objects, i, j are ints):</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">L</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="n">L1</span><span class="o">.</span><span class="n">extend</span><span class="p">(</span><span class="n">L2</span><span class="p">)</span>
<span class="n">x</span> <span class="o">=</span> <span class="n">L</span><span class="p">[</span><span class="n">i</span><span class="p">]</span>
<span class="n">x</span> <span class="o">=</span> <span class="n">L</span><span class="o">.</span><span class="n">pop</span><span class="p">()</span>
<span class="n">L1</span><span class="p">[</span><span class="n">i</span><span class="p">:</span><span class="n">j</span><span class="p">]</span> <span class="o">=</span> <span class="n">L2</span>
<span class="n">L</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span>
<span class="n">x</span> <span class="o">=</span> <span class="n">y</span>
<span class="n">x</span><span class="o">.</span><span class="n">field</span> <span class="o">=</span> <span class="n">y</span>
<span class="n">D</span><span class="p">[</span><span class="n">x</span><span class="p">]</span> <span class="o">=</span> <span class="n">y</span>
<span class="n">D1</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="n">D2</span><span class="p">)</span>
<span class="n">D</span><span class="o">.</span><span class="n">keys</span><span class="p">()</span>
</pre></div>
</div>
<p>These aren't:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">i</span> <span class="o">=</span> <span class="n">i</span><span class="o">+</span><span class="mi">1</span>
<span class="n">L</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">L</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">])</span>
<span class="n">L</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="n">L</span><span class="p">[</span><span class="n">j</span><span class="p">]</span>
<span class="n">D</span><span class="p">[</span><span class="n">x</span><span class="p">]</span> <span class="o">=</span> <span class="n">D</span><span class="p">[</span><span class="n">x</span><span class="p">]</span> <span class="o">+</span> <span class="mi">1</span>
</pre></div>
</div>
<p>Operations that replace other objects may invoke those other objects'
<a class="reference internal" href="../reference/datamodel.html#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__del__()</span></code></a> method when their reference count reaches zero, and that can
affect things. This is especially true for the mass updates to dictionaries and
lists. When in doubt, use a mutex!</p>
</section>
<section id="can-t-we-get-rid-of-the-global-interpreter-lock">
<h3><a class="toc-backref" href="#id19" role="doc-backlink">Can't we get rid of the Global Interpreter Lock?</a><a class="headerlink" href="#can-t-we-get-rid-of-the-global-interpreter-lock" title="Link to this heading">¶</a></h3>
<p>The <a class="reference internal" href="../glossary.html#term-global-interpreter-lock"><span class="xref std std-term">global interpreter lock</span></a> (GIL) is often seen as a hindrance to Python's
deployment on high-end multiprocessor server machines, because a multi-threaded
Python program effectively only uses one CPU, due to the insistence that
(almost) all Python code can only run while the GIL is held.</p>
<p>With the approval of <span class="target" id="index-2"></span><a class="pep reference external" href="https://peps.python.org/pep-0703/"><strong>PEP 703</strong></a> work is now underway to remove the GIL from the
CPython implementation of Python. Initially it will be implemented as an
optional compiler flag when building the interpreter, and so separate
builds will be available with and without the GIL. Long-term, the hope is
to settle on a single build, once the performance implications of removing the
GIL are fully understood. Python 3.13 is likely to be the first release
containing this work, although it may not be completely functional in this
release.</p>
<p>The current work to remove the GIL is based on a
<a class="reference external" href="https://github.com/colesbury/nogil">fork of Python 3.9 with the GIL removed</a>
by Sam Gross.
Prior to that,
in the days of Python 1.5, Greg Stein actually implemented a comprehensive
patch set (the "free threading" patches) that removed the GIL and replaced it
with fine-grained locking. Adam Olsen did a similar experiment
in his <a class="reference external" href="https://code.google.com/archive/p/python-safethread">python-safethread</a>
project. Unfortunately, both of these earlier experiments exhibited a sharp
drop in single-thread
performance (at least 30% slower), due to the amount of fine-grained locking
necessary to compensate for the removal of the GIL. The Python 3.9 fork
is the first attempt at removing the GIL with an acceptable performance
impact.</p>
<p>The presence of the GIL in current Python releases
doesn't mean that you can't make good use of Python on multi-CPU machines!
You just have to be creative with dividing the work up between multiple
<em>processes</em> rather than multiple <em>threads</em>. The
<a class="reference internal" href="../library/concurrent.futures.html#concurrent.futures.ProcessPoolExecutor" title="concurrent.futures.ProcessPoolExecutor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProcessPoolExecutor</span></code></a> class in the new
<a class="reference internal" href="../library/concurrent.futures.html#module-concurrent.futures" title="concurrent.futures: Execute computations concurrently using threads or processes."><code class="xref py py-mod docutils literal notranslate"><span class="pre">concurrent.futures</span></code></a> module provides an easy way of doing so; the
<a class="reference internal" href="../library/multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> module provides a lower-level API in case you want
more control over dispatching of tasks.</p>
<p>Judicious use of C extensions will also help; if you use a C extension to
perform a time-consuming task, the extension can release the GIL while the
thread of execution is in the C code and allow other threads to get some work
done. Some standard library modules such as <a class="reference internal" href="../library/zlib.html#module-zlib" title="zlib: Low-level interface to compression and decompression routines compatible with gzip."><code class="xref py py-mod docutils literal notranslate"><span class="pre">zlib</span></code></a> and <a class="reference internal" href="../library/hashlib.html#module-hashlib" title="hashlib: Secure hash and message digest algorithms."><code class="xref py py-mod docutils literal notranslate"><span class="pre">hashlib</span></code></a>
already do this.</p>
<p>An alternative approach to reducing the impact of the GIL is
to make the GIL a per-interpreter-state lock rather than truly global.
This was <a class="reference internal" href="../whatsnew/3.12.html#whatsnew312-pep684"><span class="std std-ref">first implemented in Python 3.12</span></a> and is
available in the C API. A Python interface to it is expected in Python 3.13.
The main limitation to it at the moment is likely to be 3rd party extension
modules, since these must be written with multiple interpreters in mind in
order to be usable, so many older extension modules will not be usable.</p>
</section>
</section>
<section id="input-and-output">
<h2><a class="toc-backref" href="#id20" role="doc-backlink">Input and Output</a><a class="headerlink" href="#input-and-output" title="Link to this heading">¶</a></h2>
<section id="how-do-i-delete-a-file-and-other-file-questions">
<h3><a class="toc-backref" href="#id21" role="doc-backlink">How do I delete a file? (And other file questions...)</a><a class="headerlink" href="#how-do-i-delete-a-file-and-other-file-questions" title="Link to this heading">¶</a></h3>
<p>Use <code class="docutils literal notranslate"><span class="pre">os.remove(filename)</span></code> or <code class="docutils literal notranslate"><span class="pre">os.unlink(filename)</span></code>; for documentation, see
the <a class="reference internal" href="../library/os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a> module. The two functions are identical; <a class="reference internal" href="../library/os.html#os.unlink" title="os.unlink"><code class="xref py py-func docutils literal notranslate"><span class="pre">unlink()</span></code></a> is simply
the name of the Unix system call for this function.</p>
<p>To remove a directory, use <a class="reference internal" href="../library/os.html#os.rmdir" title="os.rmdir"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.rmdir()</span></code></a>; use <a class="reference internal" href="../library/os.html#os.mkdir" title="os.mkdir"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.mkdir()</span></code></a> to create one.
<code class="docutils literal notranslate"><span class="pre">os.makedirs(path)</span></code> will create any intermediate directories in <code class="docutils literal notranslate"><span class="pre">path</span></code> that
don't exist. <code class="docutils literal notranslate"><span class="pre">os.removedirs(path)</span></code> will remove intermediate directories as
long as they're empty; if you want to delete an entire directory tree and its
contents, use <a class="reference internal" href="../library/shutil.html#shutil.rmtree" title="shutil.rmtree"><code class="xref py py-func docutils literal notranslate"><span class="pre">shutil.rmtree()</span></code></a>.</p>
<p>To rename a file, use <code class="docutils literal notranslate"><span class="pre">os.rename(old_path,</span> <span class="pre">new_path)</span></code>.</p>
<p>To truncate a file, open it using <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">=</span> <span class="pre">open(filename,</span> <span class="pre">"rb+")</span></code>, and use
<code class="docutils literal notranslate"><span class="pre">f.truncate(offset)</span></code>; offset defaults to the current seek position. There's
also <code class="docutils literal notranslate"><span class="pre">os.ftruncate(fd,</span> <span class="pre">offset)</span></code> for files opened with <a class="reference internal" href="../library/os.html#os.open" title="os.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.open()</span></code></a>, where
<em>fd</em> is the file descriptor (a small integer).</p>
<p>The <a class="reference internal" href="../library/shutil.html#module-shutil" title="shutil: High-level file operations, including copying."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shutil</span></code></a> module also contains a number of functions to work on files
including <a class="reference internal" href="../library/shutil.html#shutil.copyfile" title="shutil.copyfile"><code class="xref py py-func docutils literal notranslate"><span class="pre">copyfile()</span></code></a>, <a class="reference internal" href="../library/shutil.html#shutil.copytree" title="shutil.copytree"><code class="xref py py-func docutils literal notranslate"><span class="pre">copytree()</span></code></a>, and
<a class="reference internal" href="../library/shutil.html#shutil.rmtree" title="shutil.rmtree"><code class="xref py py-func docutils literal notranslate"><span class="pre">rmtree()</span></code></a>.</p>
</section>
<section id="how-do-i-copy-a-file">
<h3><a class="toc-backref" href="#id22" role="doc-backlink">How do I copy a file?</a><a class="headerlink" href="#how-do-i-copy-a-file" title="Link to this heading">¶</a></h3>
<p>The <a class="reference internal" href="../library/shutil.html#module-shutil" title="shutil: High-level file operations, including copying."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shutil</span></code></a> module contains a <a class="reference internal" href="../library/shutil.html#shutil.copyfile" title="shutil.copyfile"><code class="xref py py-func docutils literal notranslate"><span class="pre">copyfile()</span></code></a> function.
Note that on Windows NTFS volumes, it does not copy
<a class="reference external" href="https://en.wikipedia.org/wiki/NTFS#Alternate_data_stream_(ADS)">alternate data streams</a>
nor <a class="reference external" href="https://en.wikipedia.org/wiki/Resource_fork">resource forks</a>
on macOS HFS+ volumes, though both are now rarely used.
It also doesn't copy file permissions and metadata, though using
<a class="reference internal" href="../library/shutil.html#shutil.copy2" title="shutil.copy2"><code class="xref py py-func docutils literal notranslate"><span class="pre">shutil.copy2()</span></code></a> instead will preserve most (though not all) of it.</p>
</section>
<section id="how-do-i-read-or-write-binary-data">
<h3><a class="toc-backref" href="#id23" role="doc-backlink">How do I read (or write) binary data?</a><a class="headerlink" href="#how-do-i-read-or-write-binary-data" title="Link to this heading">¶</a></h3>
<p>To read or write complex binary data formats, it's best to use the <a class="reference internal" href="../library/struct.html#module-struct" title="struct: Interpret bytes as packed binary data."><code class="xref py py-mod docutils literal notranslate"><span class="pre">struct</span></code></a>
module. It allows you to take a string containing binary data (usually numbers)
and convert it to Python objects; and vice versa.</p>
<p>For example, the following code reads two 2-byte integers and one 4-byte integer
in big-endian format from a file:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">struct</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">,</span> <span class="s2">"rb"</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">s</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">8</span><span class="p">)</span>
<span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">,</span> <span class="n">z</span> <span class="o">=</span> <span class="n">struct</span><span class="o">.</span><span class="n">unpack</span><span class="p">(</span><span class="s2">">hhl"</span><span class="p">,</span> <span class="n">s</span><span class="p">)</span>
</pre></div>
</div>
<p>The '>' in the format string forces big-endian data; the letter 'h' reads one
"short integer" (2 bytes), and 'l' reads one "long integer" (4 bytes) from the
string.</p>
<p>For data that is more regular (e.g. a homogeneous list of ints or floats),
you can also use the <a class="reference internal" href="../library/array.html#module-array" title="array: Space efficient arrays of uniformly typed numeric values."><code class="xref py py-mod docutils literal notranslate"><span class="pre">array</span></code></a> module.</p>
<div class="admonition note">
<p class="admonition-title">توجه</p>
<p>To read and write binary data, it is mandatory to open the file in
binary mode (here, passing <code class="docutils literal notranslate"><span class="pre">"rb"</span></code> to <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a>). If you use
<code class="docutils literal notranslate"><span class="pre">"r"</span></code> instead (the default), the file will be open in text mode
and <code class="docutils literal notranslate"><span class="pre">f.read()</span></code> will return <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> objects rather than
<a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> objects.</p>
</div>
</section>
<section id="i-can-t-seem-to-use-os-read-on-a-pipe-created-with-os-popen-why">
<h3><a class="toc-backref" href="#id24" role="doc-backlink">I can't seem to use os.read() on a pipe created with os.popen(); why?</a><a class="headerlink" href="#i-can-t-seem-to-use-os-read-on-a-pipe-created-with-os-popen-why" title="Link to this heading">¶</a></h3>
<p><a class="reference internal" href="../library/os.html#os.read" title="os.read"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.read()</span></code></a> is a low-level function which takes a file descriptor, a small
integer representing the opened file. <a class="reference internal" href="../library/os.html#os.popen" title="os.popen"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.popen()</span></code></a> creates a high-level
file object, the same type returned by the built-in <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> function.
Thus, to read <em>n</em> bytes from a pipe <em>p</em> created with <code class="xref py py-func docutils literal notranslate"><span class="pre">os.popen()</span></code>, you need to
use <code class="docutils literal notranslate"><span class="pre">p.read(n)</span></code>.</p>
</section>
<section id="how-do-i-access-the-serial-rs232-port">
<h3><a class="toc-backref" href="#id25" role="doc-backlink">How do I access the serial (RS232) port?</a><a class="headerlink" href="#how-do-i-access-the-serial-rs232-port" title="Link to this heading">¶</a></h3>
<p>For Win32, OSX, Linux, BSD, Jython, IronPython:</p>
<blockquote>
<div><p><a class="extlink-pypi reference external" href="https://pypi.org/project/pyserial/">pyserial</a></p>
</div></blockquote>
<p>For Unix, see a Usenet post by Mitch Chapman:</p>
<blockquote>
<div><p><a class="reference external" href="https://groups.google.com/groups?selm=34A04430.CF9@ohioee.com">https://groups.google.com/groups?selm=34A04430.CF9@ohioee.com</a></p>
</div></blockquote>
</section>
<section id="why-doesn-t-closing-sys-stdout-stdin-stderr-really-close-it">
<h3><a class="toc-backref" href="#id26" role="doc-backlink">Why doesn't closing sys.stdout (stdin, stderr) really close it?</a><a class="headerlink" href="#why-doesn-t-closing-sys-stdout-stdin-stderr-really-close-it" title="Link to this heading">¶</a></h3>
<p>Python <a class="reference internal" href="../glossary.html#term-file-object"><span class="xref std std-term">file objects</span></a> are a high-level layer of
abstraction on low-level C file descriptors.</p>
<p>For most file objects you create in Python via the built-in <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a>
function, <code class="docutils literal notranslate"><span class="pre">f.close()</span></code> marks the Python file object as being closed from
Python's point of view, and also arranges to close the underlying C file
descriptor. This also happens automatically in <code class="docutils literal notranslate"><span class="pre">f</span></code>'s destructor, when
<code class="docutils literal notranslate"><span class="pre">f</span></code> becomes garbage.</p>
<p>But stdin, stdout and stderr are treated specially by Python, because of the
special status also given to them by C. Running <code class="docutils literal notranslate"><span class="pre">sys.stdout.close()</span></code> marks
the Python-level file object as being closed, but does <em>not</em> close the
associated C file descriptor.</p>
<p>To close the underlying C file descriptor for one of these three, you should
first be sure that's what you really want to do (e.g., you may confuse
extension modules trying to do I/O). If it is, use <a class="reference internal" href="../library/os.html#os.close" title="os.close"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.close()</span></code></a>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">os</span><span class="o">.</span><span class="n">close</span><span class="p">(</span><span class="n">stdin</span><span class="o">.</span><span class="n">fileno</span><span class="p">())</span>
<span class="n">os</span><span class="o">.</span><span class="n">close</span><span class="p">(</span><span class="n">stdout</span><span class="o">.</span><span class="n">fileno</span><span class="p">())</span>
<span class="n">os</span><span class="o">.</span><span class="n">close</span><span class="p">(</span><span class="n">stderr</span><span class="o">.</span><span class="n">fileno</span><span class="p">())</span>
</pre></div>
</div>
<p>Or you can use the numeric constants 0, 1 and 2, respectively.</p>
</section>
</section>
<section id="network-internet-programming">
<h2><a class="toc-backref" href="#id27" role="doc-backlink">Network/Internet Programming</a><a class="headerlink" href="#network-internet-programming" title="Link to this heading">¶</a></h2>
<section id="what-www-tools-are-there-for-python">
<h3><a class="toc-backref" href="#id28" role="doc-backlink">What WWW tools are there for Python?</a><a class="headerlink" href="#what-www-tools-are-there-for-python" title="Link to this heading">¶</a></h3>
<p>See the chapters titled <a class="reference internal" href="../library/internet.html#internet"><span class="std std-ref">Internet Protocols and Support</span></a> and <a class="reference internal" href="../library/netdata.html#netdata"><span class="std std-ref">Internet Data Handling</span></a> in the Library
Reference Manual. Python has many modules that will help you build server-side
and client-side web systems.</p>
<p>A summary of available frameworks is maintained by Paul Boddie at
<a class="reference external" href="https://wiki.python.org/moin/WebProgramming">https://wiki.python.org/moin/WebProgramming</a>.</p>
</section>
<section id="what-module-should-i-use-to-help-with-generating-html">
<h3><a class="toc-backref" href="#id29" role="doc-backlink">What module should I use to help with generating HTML?</a><a class="headerlink" href="#what-module-should-i-use-to-help-with-generating-html" title="Link to this heading">¶</a></h3>
<p>You can find a collection of useful links on the <a class="reference external" href="https://wiki.python.org/moin/WebProgramming">Web Programming wiki page</a>.</p>
</section>
<section id="how-do-i-send-mail-from-a-python-script">
<h3><a class="toc-backref" href="#id30" role="doc-backlink">How do I send mail from a Python script?</a><a class="headerlink" href="#how-do-i-send-mail-from-a-python-script" title="Link to this heading">¶</a></h3>
<p>Use the standard library module <a class="reference internal" href="../library/smtplib.html#module-smtplib" title="smtplib: SMTP protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">smtplib</span></code></a>.</p>
<p>Here's a very simple interactive mail sender that uses it. This method will
work on any host that supports an SMTP listener.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">sys</span><span class="o">,</span><span class="w"> </span><span class="nn">smtplib</span>
<span class="n">fromaddr</span> <span class="o">=</span> <span class="nb">input</span><span class="p">(</span><span class="s2">"From: "</span><span class="p">)</span>
<span class="n">toaddrs</span> <span class="o">=</span> <span class="nb">input</span><span class="p">(</span><span class="s2">"To: "</span><span class="p">)</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">','</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"Enter message, end with ^D:"</span><span class="p">)</span>
<span class="n">msg</span> <span class="o">=</span> <span class="s1">''</span>
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="n">line</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">stdin</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">line</span><span class="p">:</span>
<span class="k">break</span>
<span class="n">msg</span> <span class="o">+=</span> <span class="n">line</span>
<span class="c1"># The actual mail send</span>
<span class="n">server</span> <span class="o">=</span> <span class="n">smtplib</span><span class="o">.</span><span class="n">SMTP</span><span class="p">(</span><span class="s1">'localhost'</span><span class="p">)</span>
<span class="n">server</span><span class="o">.</span><span class="n">sendmail</span><span class="p">(</span><span class="n">fromaddr</span><span class="p">,</span> <span class="n">toaddrs</span><span class="p">,</span> <span class="n">msg</span><span class="p">)</span>
<span class="n">server</span><span class="o">.</span><span class="n">quit</span><span class="p">()</span>
</pre></div>
</div>
<p>A Unix-only alternative uses sendmail. The location of the sendmail program
varies between systems; sometimes it is <code class="docutils literal notranslate"><span class="pre">/usr/lib/sendmail</span></code>, sometimes
<code class="docutils literal notranslate"><span class="pre">/usr/sbin/sendmail</span></code>. The sendmail manual page will help you out. Here's
some sample code:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">os</span>
<span class="n">SENDMAIL</span> <span class="o">=</span> <span class="s2">"/usr/sbin/sendmail"</span> <span class="c1"># sendmail location</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">popen</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2"> -t -i"</span> <span class="o">%</span> <span class="n">SENDMAIL</span><span class="p">,</span> <span class="s2">"w"</span><span class="p">)</span>
<span class="n">p</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"To: receiver@example.com</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="n">p</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"Subject: test</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="n">p</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span> <span class="c1"># blank line separating headers from body</span>
<span class="n">p</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"Some text</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="n">p</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s2">"some more text</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="n">sts</span> <span class="o">=</span> <span class="n">p</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">if</span> <span class="n">sts</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"Sendmail exit status"</span><span class="p">,</span> <span class="n">sts</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="how-do-i-avoid-blocking-in-the-connect-method-of-a-socket">
<h3><a class="toc-backref" href="#id31" role="doc-backlink">How do I avoid blocking in the connect() method of a socket?</a><a class="headerlink" href="#how-do-i-avoid-blocking-in-the-connect-method-of-a-socket" title="Link to this heading">¶</a></h3>
<p>The <a class="reference internal" href="../library/select.html#module-select" title="select: Wait for I/O completion on multiple streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">select</span></code></a> module is commonly used to help with asynchronous I/O on
sockets.</p>
<p>To prevent the TCP connect from blocking, you can set the socket to non-blocking
mode. Then when you do the <a class="reference internal" href="../library/socket.html#socket.socket.connect" title="socket.socket.connect"><code class="xref py py-meth docutils literal notranslate"><span class="pre">connect()</span></code></a>,
you will either connect immediately
(unlikely) or get an exception that contains the error number as <code class="docutils literal notranslate"><span class="pre">.errno</span></code>.
<code class="docutils literal notranslate"><span class="pre">errno.EINPROGRESS</span></code> indicates that the connection is in progress, but hasn't
finished yet. Different OSes will return different values, so you're going to
have to check what's returned on your system.</p>
<p>You can use the <a class="reference internal" href="../library/socket.html#socket.socket.connect_ex" title="socket.socket.connect_ex"><code class="xref py py-meth docutils literal notranslate"><span class="pre">connect_ex()</span></code></a> method
to avoid creating an exception.
It will just return the errno value.
To poll, you can call <code class="xref py py-meth docutils literal notranslate"><span class="pre">connect_ex()</span></code> again later
-- <code class="docutils literal notranslate"><span class="pre">0</span></code> or <code class="docutils literal notranslate"><span class="pre">errno.EISCONN</span></code> indicate that you're connected -- or you can pass this
socket to <a class="reference internal" href="../library/select.html#select.select" title="select.select"><code class="xref py py-meth docutils literal notranslate"><span class="pre">select.select()</span></code></a> to check if it's writable.</p>
<div class="admonition note">
<p class="admonition-title">توجه</p>
<p>The <a class="reference internal" href="../library/asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code></a> module provides a general purpose single-threaded and
concurrent asynchronous library, which can be used for writing non-blocking
network code.
The third-party <a class="reference external" href="https://twisted.org/">Twisted</a> library is
a popular and feature-rich alternative.</p>
</div>
</section>
</section>
<section id="databases">
<h2><a class="toc-backref" href="#id32" role="doc-backlink">Databases</a><a class="headerlink" href="#databases" title="Link to this heading">¶</a></h2>
<section id="are-there-any-interfaces-to-database-packages-in-python">
<h3><a class="toc-backref" href="#id33" role="doc-backlink">Are there any interfaces to database packages in Python?</a><a class="headerlink" href="#are-there-any-interfaces-to-database-packages-in-python" title="Link to this heading">¶</a></h3>
<p>Yes.</p>
<p>Interfaces to disk-based hashes such as <a class="reference internal" href="../library/dbm.html#module-dbm.ndbm" title="dbm.ndbm: The New Database Manager"><code class="xref py py-mod docutils literal notranslate"><span class="pre">DBM</span></code></a> and <a class="reference internal" href="../library/dbm.html#module-dbm.gnu" title="dbm.gnu: GNU database manager"><code class="xref py py-mod docutils literal notranslate"><span class="pre">GDBM</span></code></a> are also included with standard Python. There is also the
<a class="reference internal" href="../library/sqlite3.html#module-sqlite3" title="sqlite3: A DB-API 2.0 implementation using SQLite 3.x."><code class="xref py py-mod docutils literal notranslate"><span class="pre">sqlite3</span></code></a> module, which provides a lightweight disk-based relational
database.</p>
<p>Support for most relational databases is available. See the
<a class="reference external" href="https://wiki.python.org/moin/DatabaseProgramming">DatabaseProgramming wiki page</a> for details.</p>
</section>
<section id="how-do-you-implement-persistent-objects-in-python">
<h3><a class="toc-backref" href="#id34" role="doc-backlink">How do you implement persistent objects in Python?</a><a class="headerlink" href="#how-do-you-implement-persistent-objects-in-python" title="Link to this heading">¶</a></h3>
<p>The <a class="reference internal" href="../library/pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> library module solves this in a very general way (though you
still can't store things like open files, sockets or windows), and the
<a class="reference internal" href="../library/shelve.html#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code></a> library module uses pickle and (g)dbm to create persistent
mappings containing arbitrary Python objects.</p>
</section>
</section>
<section id="mathematics-and-numerics">
<h2><a class="toc-backref" href="#id35" role="doc-backlink">Mathematics and Numerics</a><a class="headerlink" href="#mathematics-and-numerics" title="Link to this heading">¶</a></h2>
<section id="how-do-i-generate-random-numbers-in-python">
<h3><a class="toc-backref" href="#id36" role="doc-backlink">How do I generate random numbers in Python?</a><a class="headerlink" href="#how-do-i-generate-random-numbers-in-python" title="Link to this heading">¶</a></h3>
<p>The standard module <a class="reference internal" href="../library/random.html#module-random" title="random: Generate pseudo-random numbers with various common distributions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">random</span></code></a> implements a random number generator. Usage
is simple:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">random</span>
<span class="n">random</span><span class="o">.</span><span class="n">random</span><span class="p">()</span>
</pre></div>
</div>
<p>This returns a random floating-point number in the range [0, 1).</p>
<p>There are also many other specialized generators in this module, such as:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">randrange(a,</span> <span class="pre">b)</span></code> chooses an integer in the range [a, b).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">uniform(a,</span> <span class="pre">b)</span></code> chooses a floating-point number in the range [a, b).</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">normalvariate(mean,</span> <span class="pre">sdev)</span></code> samples the normal (Gaussian) distribution.</p></li>
</ul>
<p>Some higher-level functions operate on sequences directly, such as:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">choice(S)</span></code> chooses a random element from a given sequence.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">shuffle(L)</span></code> shuffles a list in-place, i.e. permutes it randomly.</p></li>
</ul>
<p>There's also a <code class="docutils literal notranslate"><span class="pre">Random</span></code> class you can instantiate to create independent
multiple random number generators.</p>
</section>
</section>
</section>
<div class="clearer"></div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="Main">
<div class="sphinxsidebarwrapper">
<div>
<h3><a href="../contents.html">فهرست عناوین</a></h3>
<ul>
<li><a class="reference internal" href="#">Library and Extension FAQ</a><ul>
<li><a class="reference internal" href="#general-library-questions">General Library Questions</a></li>
<li><a class="reference internal" href="#common-tasks">Common tasks</a></li>
<li><a class="reference internal" href="#threads">Threads</a></li>
<li><a class="reference internal" href="#input-and-output">Input and Output</a></li>
<li><a class="reference internal" href="#network-internet-programming">Network/Internet Programming</a></li>
<li><a class="reference internal" href="#databases">Databases</a></li>
<li><a class="reference internal" href="#mathematics-and-numerics">Mathematics and Numerics</a></li>
</ul>
</li>
</ul>
</div>
<div>
<h4>موضوع قبلی</h4>
<p class="topless"><a href="design.html"
title="فصل قبلی">Design and History FAQ</a></p>
</div>
<div>
<h4>موضوع بعدی</h4>
<p class="topless"><a href="extending.html"
title="فصل بعدی">Extending/Embedding FAQ</a></p>
</div>
<script>
document.addEventListener('DOMContentLoaded', () => {
const title = document.querySelector('meta[property="og:title"]').content;
const elements = document.querySelectorAll('.improvepage');
const pageurl = window.location.href.split('?')[0];
elements.forEach(element => {
const url = new URL(element.href.split('?')[0].replace("-nojs", ""));
url.searchParams.set('pagetitle', title);
url.searchParams.set('pageurl', pageurl);
url.searchParams.set('pagesource', "faq/library.rst");
element.href = url.toString();
});
});
</script>
<div role="note" aria-label="source link">
<h3>این صفحه</h3>
<ul class="this-page-menu">
<li><a href="../bugs.html">گزارش یک اشکال</a></li>
<li><a class="improvepage" href="../improve-page-nojs.html">بهبود این صفحه</a></li>
<li>
<a href="https://github.com/python/cpython/blob/main/Doc/faq/library.rst?plain=1"
rel="nofollow">نمایش منبع
</a>
</li>
<li>
<a href="https://github.com/python/python-docs-fa/blob/3.14/faq/library.po?plain=1"
rel="nofollow">نمایش منبع ترجمه</a>
</li>
</ul>
</div>
</div>
<div id="sidebarbutton" title="تا کردن نوار کناره">
<span>«</span>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="related" role="navigation" aria-label="Related">
<h3>ناوبری</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="فهرست کلی"
>فهرست</a></li>
<li class="right" >
<a href="../py-modindex.html" title="نمایه ی ماژول های پایتون"
>ماژول ها</a> |</li>
<li class="right" >
<a href="extending.html" title="Extending/Embedding FAQ"
>بعدی</a> |</li>
<li class="right" >
<a href="design.html" title="Design and History FAQ"
>قبلی</a> |</li>
<li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li class="switchers">
<div class="language_switcher_placeholder"></div>
<div class="version_switcher_placeholder"></div>
</li>
<li>
</li>
<li id="cpython-language-and-version">
<a href="../index.html">3.14.6 Documentation</a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >Python Frequently Asked Questions</a> »</li>
<li class="nav-item nav-item-this"><a href="">Library and Extension FAQ</a></li>
<li class="right">
<div class="inline-search" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="جستجو سریع" aria-label="جستجو سریع" type="search" name="q" id="search-box">
<input type="submit" value="برو">
</form>
</div>
|
</li>
<li class="right">
<label class="theme-selector-label">
Theme
<select class="theme-selector" oninput="activateTheme(this.value)">
<option value="auto" selected>Auto</option>
<option value="light">Light</option>
<option value="dark">Dark</option>
</select>
</label> |</li>