Repository navigation
Expand file tree
/
Copy pathcontextlib.po
More file actions
865 lines (734 loc) · 29.3 KB
/
Copy pathcontextlib.po
File metadata and controls
865 lines (734 loc) · 29.3 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
# SOME DESCRIPTIVE TITLE.
# Copyright (C) 2001-2022, Python Software Foundation
# This file is distributed under the same license as the Python package.
#
# Translators:
msgid ""
msgstr ""
"Project-Id-Version: Python 3.12\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2023-07-17 17:39+0800\n"
"PO-Revision-Date: 2018-05-23 14:41+0000\n"
"Last-Translator: Adrian Liaw <adrianliaw2000@gmail.com>\n"
"Language-Team: Chinese - TAIWAN (https://github.com/python/python-docs-zh-"
"tw)\n"
"Language: zh_TW\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=1; plural=0;\n"
#: ../../library/contextlib.rst:2
msgid ""
":mod:`!contextlib` --- Utilities for :keyword:`!with`\\ -statement contexts"
msgstr ""
#: ../../library/contextlib.rst:7
msgid "**Source code:** :source:`Lib/contextlib.py`"
msgstr "**原始碼：**\\ :source:`Lib/contextlib.py`"
#: ../../library/contextlib.rst:11
msgid ""
"This module provides utilities for common tasks involving the :keyword:"
"`with` statement. For more information see also :ref:`typecontextmanager` "
"and :ref:`context-managers`."
msgstr ""
#: ../../library/contextlib.rst:17
msgid "Utilities"
msgstr ""
#: ../../library/contextlib.rst:19
msgid "Functions and classes provided:"
msgstr ""
#: ../../library/contextlib.rst:23
msgid ""
"An :term:`abstract base class` for classes that implement :meth:`object."
"__enter__` and :meth:`object.__exit__`. A default implementation for :meth:"
"`object.__enter__` is provided which returns ``self`` while :meth:`object."
"__exit__` is an abstract method which by default returns ``None``. See also "
"the definition of :ref:`typecontextmanager`."
msgstr ""
#: ../../library/contextlib.rst:34
msgid ""
"An :term:`abstract base class` for classes that implement :meth:`object."
"__aenter__` and :meth:`object.__aexit__`. A default implementation for :meth:"
"`object.__aenter__` is provided which returns ``self`` while :meth:`object."
"__aexit__` is an abstract method which by default returns ``None``. See also "
"the definition of :ref:`async-context-managers`."
msgstr ""
#: ../../library/contextlib.rst:46
msgid ""
"This function is a :term:`decorator` that can be used to define a factory "
"function for :keyword:`with` statement context managers, without needing to "
"create a class or separate :meth:`__enter__` and :meth:`__exit__` methods."
msgstr ""
#: ../../library/contextlib.rst:50
msgid ""
"While many objects natively support use in with statements, sometimes a "
"resource needs to be managed that isn't a context manager in its own right, "
"and doesn't implement a ``close()`` method for use with ``contextlib."
"closing``"
msgstr ""
#: ../../library/contextlib.rst:54
msgid ""
"An abstract example would be the following to ensure correct resource "
"management::"
msgstr ""
#: ../../library/contextlib.rst:69
msgid "The function can then be used like this::"
msgstr ""
#: ../../library/contextlib.rst:75
msgid ""
"The function being decorated must return a :term:`generator`-iterator when "
"called. This iterator must yield exactly one value, which will be bound to "
"the targets in the :keyword:`with` statement's :keyword:`!as` clause, if any."
msgstr ""
#: ../../library/contextlib.rst:79
msgid ""
"At the point where the generator yields, the block nested in the :keyword:"
"`with` statement is executed. The generator is then resumed after the block "
"is exited. If an unhandled exception occurs in the block, it is reraised "
"inside the generator at the point where the yield occurred. Thus, you can "
"use a :keyword:`try`...\\ :keyword:`except`...\\ :keyword:`finally` "
"statement to trap the error (if any), or ensure that some cleanup takes "
"place. If an exception is trapped merely in order to log it or to perform "
"some action (rather than to suppress it entirely), the generator must "
"reraise that exception. Otherwise the generator context manager will "
"indicate to the :keyword:`!with` statement that the exception has been "
"handled, and execution will resume with the statement immediately following "
"the :keyword:`!with` statement."
msgstr ""
#: ../../library/contextlib.rst:91
msgid ""
":func:`contextmanager` uses :class:`ContextDecorator` so the context "
"managers it creates can be used as decorators as well as in :keyword:`with` "
"statements. When used as a decorator, a new generator instance is implicitly "
"created on each function call (this allows the otherwise \"one-shot\" "
"context managers created by :func:`contextmanager` to meet the requirement "
"that context managers support multiple invocations in order to be used as "
"decorators)."
msgstr ""
#: ../../library/contextlib.rst:98
msgid "Use of :class:`ContextDecorator`."
msgstr ""
#: ../../library/contextlib.rst:104
msgid ""
"Similar to :func:`~contextlib.contextmanager`, but creates an :ref:"
"`asynchronous context manager <async-context-managers>`."
msgstr ""
#: ../../library/contextlib.rst:107
msgid ""
"This function is a :term:`decorator` that can be used to define a factory "
"function for :keyword:`async with` statement asynchronous context managers, "
"without needing to create a class or separate :meth:`__aenter__` and :meth:"
"`__aexit__` methods. It must be applied to an :term:`asynchronous generator` "
"function."
msgstr ""
#: ../../library/contextlib.rst:113
msgid "A simple example::"
msgstr ""
"一個簡單範例：\n"
"\n"
"::"
#: ../../library/contextlib.rst:131
msgid ""
"Context managers defined with :func:`asynccontextmanager` can be used either "
"as decorators or with :keyword:`async with` statements::"
msgstr ""
#: ../../library/contextlib.rst:149
msgid ""
"When used as a decorator, a new generator instance is implicitly created on "
"each function call. This allows the otherwise \"one-shot\" context managers "
"created by :func:`asynccontextmanager` to meet the requirement that context "
"managers support multiple invocations in order to be used as decorators."
msgstr ""
#: ../../library/contextlib.rst:154
msgid ""
"Async context managers created with :func:`asynccontextmanager` can be used "
"as decorators."
msgstr ""
#: ../../library/contextlib.rst:161
msgid ""
"Return a context manager that closes *thing* upon completion of the block. "
"This is basically equivalent to::"
msgstr ""
#: ../../library/contextlib.rst:173
msgid "And lets you write code like this::"
msgstr ""
#: ../../library/contextlib.rst:182
msgid ""
"without needing to explicitly close ``page``. Even if an error occurs, "
"``page.close()`` will be called when the :keyword:`with` block is exited."
msgstr ""
#: ../../library/contextlib.rst:188
msgid ""
"Return an async context manager that calls the ``aclose()`` method of "
"*thing* upon completion of the block. This is basically equivalent to::"
msgstr ""
#: ../../library/contextlib.rst:200
msgid ""
"Significantly, ``aclosing()`` supports deterministic cleanup of async "
"generators when they happen to exit early by :keyword:`break` or an "
"exception. For example::"
msgstr ""
#: ../../library/contextlib.rst:211
msgid ""
"This pattern ensures that the generator's async exit code is executed in the "
"same context as its iterations (so that exceptions and context variables "
"work as expected, and the exit code isn't run after the lifetime of some "
"task it depends on)."
msgstr ""
#: ../../library/contextlib.rst:223
msgid ""
"Return a context manager that returns *enter_result* from ``__enter__``, but "
"otherwise does nothing. It is intended to be used as a stand-in for an "
"optional context manager, for example::"
msgstr ""
#: ../../library/contextlib.rst:237
msgid "An example using *enter_result*::"
msgstr ""
"一個使用 *enter_result* 的範例：\n"
"\n"
"::"
#: ../../library/contextlib.rst:250
msgid ""
"It can also be used as a stand-in for :ref:`asynchronous context managers "
"<async-context-managers>`::"
msgstr ""
#: ../../library/contextlib.rst:266
msgid ":term:`asynchronous context manager` support was added."
msgstr ""
#: ../../library/contextlib.rst:273
msgid ""
"Return a context manager that suppresses any of the specified exceptions if "
"they occur in the body of a :keyword:`!with` statement and then resumes "
"execution with the first statement following the end of the :keyword:`!with` "
"statement."
msgstr ""
#: ../../library/contextlib.rst:278
msgid ""
"As with any other mechanism that completely suppresses exceptions, this "
"context manager should be used only to cover very specific errors where "
"silently continuing with program execution is known to be the right thing to "
"do."
msgstr ""
#: ../../library/contextlib.rst:283
msgid "For example::"
msgstr ""
"舉例來說：\n"
"\n"
"::"
#: ../../library/contextlib.rst:293
msgid "This code is equivalent to::"
msgstr ""
#: ../../library/contextlib.rst:305 ../../library/contextlib.rst:352
#: ../../library/contextlib.rst:362 ../../library/contextlib.rst:379
msgid "This context manager is :ref:`reentrant <reentrant-cms>`."
msgstr ""
#: ../../library/contextlib.rst:307
msgid ""
"If the code within the :keyword:`!with` block raises an :exc:"
"`ExceptionGroup`, suppressed exceptions are removed from the group. If any "
"exceptions in the group are not suppressed, a group containing them is re-"
"raised."
msgstr ""
#: ../../library/contextlib.rst:313
msgid ""
"``suppress`` now supports suppressing exceptions raised as part of an :exc:"
"`ExceptionGroup`."
msgstr ""
#: ../../library/contextlib.rst:319
msgid ""
"Context manager for temporarily redirecting :data:`sys.stdout` to another "
"file or file-like object."
msgstr ""
#: ../../library/contextlib.rst:322
msgid ""
"This tool adds flexibility to existing functions or classes whose output is "
"hardwired to stdout."
msgstr ""
#: ../../library/contextlib.rst:325
msgid ""
"For example, the output of :func:`help` normally is sent to *sys.stdout*. "
"You can capture that output in a string by redirecting the output to an :"
"class:`io.StringIO` object. The replacement stream is returned from the "
"``__enter__`` method and so is available as the target of the :keyword:"
"`with` statement::"
msgstr ""
#: ../../library/contextlib.rst:335
msgid ""
"To send the output of :func:`help` to a file on disk, redirect the output to "
"a regular file::"
msgstr ""
#: ../../library/contextlib.rst:342
msgid "To send the output of :func:`help` to *sys.stderr*::"
msgstr ""
#: ../../library/contextlib.rst:347
msgid ""
"Note that the global side effect on :data:`sys.stdout` means that this "
"context manager is not suitable for use in library code and most threaded "
"applications. It also has no effect on the output of subprocesses. However, "
"it is still a useful approach for many utility scripts."
msgstr ""
#: ../../library/contextlib.rst:359
msgid ""
"Similar to :func:`~contextlib.redirect_stdout` but redirecting :data:`sys."
"stderr` to another file or file-like object."
msgstr ""
#: ../../library/contextlib.rst:369
msgid ""
"Non parallel-safe context manager to change the current working directory. "
"As this changes a global state, the working directory, it is not suitable "
"for use in most threaded or async contexts. It is also not suitable for most "
"non-linear code execution, like generators, where the program execution is "
"temporarily relinquished -- unless explicitly desired, you should not yield "
"when this context manager is active."
msgstr ""
#: ../../library/contextlib.rst:376
msgid ""
"This is a simple wrapper around :func:`~os.chdir`, it changes the current "
"working directory upon entering and restores the old one on exit."
msgstr ""
#: ../../library/contextlib.rst:386
msgid ""
"A base class that enables a context manager to also be used as a decorator."
msgstr ""
#: ../../library/contextlib.rst:388
msgid ""
"Context managers inheriting from ``ContextDecorator`` have to implement "
"``__enter__`` and ``__exit__`` as normal. ``__exit__`` retains its optional "
"exception handling even when used as a decorator."
msgstr ""
#: ../../library/contextlib.rst:392
msgid ""
"``ContextDecorator`` is used by :func:`contextmanager`, so you get this "
"functionality automatically."
msgstr ""
#: ../../library/contextlib.rst:395
msgid "Example of ``ContextDecorator``::"
msgstr ""
"``ContextDecorator`` 範例：\n"
"\n"
"::"
#: ../../library/contextlib.rst:408 ../../library/contextlib.rst:480
msgid "The class can then be used like this::"
msgstr ""
#: ../../library/contextlib.rst:426
msgid ""
"This change is just syntactic sugar for any construct of the following form::"
msgstr ""
#: ../../library/contextlib.rst:432
msgid "``ContextDecorator`` lets you instead write::"
msgstr ""
#: ../../library/contextlib.rst:438
msgid ""
"It makes it clear that the ``cm`` applies to the whole function, rather than "
"just a piece of it (and saving an indentation level is nice, too)."
msgstr ""
#: ../../library/contextlib.rst:441
msgid ""
"Existing context managers that already have a base class can be extended by "
"using ``ContextDecorator`` as a mixin class::"
msgstr ""
#: ../../library/contextlib.rst:454
msgid ""
"As the decorated function must be able to be called multiple times, the "
"underlying context manager must support use in multiple :keyword:`with` "
"statements. If this is not the case, then the original construct with the "
"explicit :keyword:`!with` statement inside the function should be used."
msgstr ""
#: ../../library/contextlib.rst:464
msgid ""
"Similar to :class:`ContextDecorator` but only for asynchronous functions."
msgstr ""
#: ../../library/contextlib.rst:466
msgid "Example of ``AsyncContextDecorator``::"
msgstr ""
"``AsyncContextDecorator`` 範例：\n"
"\n"
"::"
#: ../../library/contextlib.rst:505
msgid ""
"A context manager that is designed to make it easy to programmatically "
"combine other context managers and cleanup functions, especially those that "
"are optional or otherwise driven by input data."
msgstr ""
#: ../../library/contextlib.rst:509
msgid ""
"For example, a set of files may easily be handled in a single with statement "
"as follows::"
msgstr ""
#: ../../library/contextlib.rst:518
msgid ""
"The :meth:`__enter__` method returns the :class:`ExitStack` instance, and "
"performs no additional operations."
msgstr ""
#: ../../library/contextlib.rst:521
msgid ""
"Each instance maintains a stack of registered callbacks that are called in "
"reverse order when the instance is closed (either explicitly or implicitly "
"at the end of a :keyword:`with` statement). Note that callbacks are *not* "
"invoked implicitly when the context stack instance is garbage collected."
msgstr ""
#: ../../library/contextlib.rst:526
msgid ""
"This stack model is used so that context managers that acquire their "
"resources in their ``__init__`` method (such as file objects) can be handled "
"correctly."
msgstr ""
#: ../../library/contextlib.rst:530
msgid ""
"Since registered callbacks are invoked in the reverse order of registration, "
"this ends up behaving as if multiple nested :keyword:`with` statements had "
"been used with the registered set of callbacks. This even extends to "
"exception handling - if an inner callback suppresses or replaces an "
"exception, then outer callbacks will be passed arguments based on that "
"updated state."
msgstr ""
#: ../../library/contextlib.rst:537
msgid ""
"This is a relatively low level API that takes care of the details of "
"correctly unwinding the stack of exit callbacks. It provides a suitable "
"foundation for higher level context managers that manipulate the exit stack "
"in application specific ways."
msgstr ""
#: ../../library/contextlib.rst:546
msgid ""
"Enters a new context manager and adds its :meth:`__exit__` method to the "
"callback stack. The return value is the result of the context manager's own :"
"meth:`__enter__` method."
msgstr ""
#: ../../library/contextlib.rst:550
msgid ""
"These context managers may suppress exceptions just as they normally would "
"if used directly as part of a :keyword:`with` statement."
msgstr ""
#: ../../library/contextlib.rst:553
msgid ""
"Raises :exc:`TypeError` instead of :exc:`AttributeError` if *cm* is not a "
"context manager."
msgstr ""
#: ../../library/contextlib.rst:559
msgid "Adds a context manager's :meth:`__exit__` method to the callback stack."
msgstr ""
#: ../../library/contextlib.rst:561
msgid ""
"As ``__enter__`` is *not* invoked, this method can be used to cover part of "
"an :meth:`__enter__` implementation with a context manager's own :meth:"
"`__exit__` method."
msgstr ""
#: ../../library/contextlib.rst:565
msgid ""
"If passed an object that is not a context manager, this method assumes it is "
"a callback with the same signature as a context manager's :meth:`__exit__` "
"method and adds it directly to the callback stack."
msgstr ""
#: ../../library/contextlib.rst:569
msgid ""
"By returning true values, these callbacks can suppress exceptions the same "
"way context manager :meth:`__exit__` methods can."
msgstr ""
#: ../../library/contextlib.rst:572
msgid ""
"The passed in object is returned from the function, allowing this method to "
"be used as a function decorator."
msgstr ""
#: ../../library/contextlib.rst:577
msgid ""
"Accepts an arbitrary callback function and arguments and adds it to the "
"callback stack."
msgstr ""
#: ../../library/contextlib.rst:580
msgid ""
"Unlike the other methods, callbacks added this way cannot suppress "
"exceptions (as they are never passed the exception details)."
msgstr ""
#: ../../library/contextlib.rst:583
msgid ""
"The passed in callback is returned from the function, allowing this method "
"to be used as a function decorator."
msgstr ""
#: ../../library/contextlib.rst:588
msgid ""
"Transfers the callback stack to a fresh :class:`ExitStack` instance and "
"returns it. No callbacks are invoked by this operation - instead, they will "
"now be invoked when the new stack is closed (either explicitly or implicitly "
"at the end of a :keyword:`with` statement)."
msgstr ""
#: ../../library/contextlib.rst:593
msgid ""
"For example, a group of files can be opened as an \"all or nothing\" "
"operation as follows::"
msgstr ""
#: ../../library/contextlib.rst:607
msgid ""
"Immediately unwinds the callback stack, invoking callbacks in the reverse "
"order of registration. For any context managers and exit callbacks "
"registered, the arguments passed in will indicate that no exception occurred."
msgstr ""
#: ../../library/contextlib.rst:614
msgid ""
"An :ref:`asynchronous context manager <async-context-managers>`, similar to :"
"class:`ExitStack`, that supports combining both synchronous and asynchronous "
"context managers, as well as having coroutines for cleanup logic."
msgstr ""
#: ../../library/contextlib.rst:619
msgid ""
"The :meth:`close` method is not implemented, :meth:`aclose` must be used "
"instead."
msgstr ""
#: ../../library/contextlib.rst:624
msgid ""
"Similar to :meth:`enter_context` but expects an asynchronous context manager."
msgstr ""
#: ../../library/contextlib.rst:627
msgid ""
"Raises :exc:`TypeError` instead of :exc:`AttributeError` if *cm* is not an "
"asynchronous context manager."
msgstr ""
#: ../../library/contextlib.rst:633
msgid ""
"Similar to :meth:`push` but expects either an asynchronous context manager "
"or a coroutine function."
msgstr ""
#: ../../library/contextlib.rst:638
msgid "Similar to :meth:`callback` but expects a coroutine function."
msgstr ""
#: ../../library/contextlib.rst:642
msgid "Similar to :meth:`close` but properly handles awaitables."
msgstr ""
#: ../../library/contextlib.rst:644
msgid "Continuing the example for :func:`asynccontextmanager`::"
msgstr ""
#: ../../library/contextlib.rst:656
msgid "Examples and Recipes"
msgstr ""
#: ../../library/contextlib.rst:658
msgid ""
"This section describes some examples and recipes for making effective use of "
"the tools provided by :mod:`contextlib`."
msgstr ""
#: ../../library/contextlib.rst:663
msgid "Supporting a variable number of context managers"
msgstr ""
#: ../../library/contextlib.rst:665
msgid ""
"The primary use case for :class:`ExitStack` is the one given in the class "
"documentation: supporting a variable number of context managers and other "
"cleanup operations in a single :keyword:`with` statement. The variability "
"may come from the number of context managers needed being driven by user "
"input (such as opening a user specified collection of files), or from some "
"of the context managers being optional::"
msgstr ""
#: ../../library/contextlib.rst:680
msgid ""
"As shown, :class:`ExitStack` also makes it quite easy to use :keyword:`with` "
"statements to manage arbitrary resources that don't natively support the "
"context management protocol."
msgstr ""
#: ../../library/contextlib.rst:686
msgid "Catching exceptions from ``__enter__`` methods"
msgstr ""
#: ../../library/contextlib.rst:688
msgid ""
"It is occasionally desirable to catch exceptions from an ``__enter__`` "
"method implementation, *without* inadvertently catching exceptions from the :"
"keyword:`with` statement body or the context manager's ``__exit__`` method. "
"By using :class:`ExitStack` the steps in the context management protocol can "
"be separated slightly in order to allow this::"
msgstr ""
#: ../../library/contextlib.rst:703
msgid ""
"Actually needing to do this is likely to indicate that the underlying API "
"should be providing a direct resource management interface for use with :"
"keyword:`try`/:keyword:`except`/:keyword:`finally` statements, but not all "
"APIs are well designed in that regard. When a context manager is the only "
"resource management API provided, then :class:`ExitStack` can make it easier "
"to handle various situations that can't be handled directly in a :keyword:"
"`with` statement."
msgstr ""
#: ../../library/contextlib.rst:713
msgid "Cleaning up in an ``__enter__`` implementation"
msgstr ""
#: ../../library/contextlib.rst:715
msgid ""
"As noted in the documentation of :meth:`ExitStack.push`, this method can be "
"useful in cleaning up an already allocated resource if later steps in the :"
"meth:`__enter__` implementation fail."
msgstr ""
#: ../../library/contextlib.rst:719
msgid ""
"Here's an example of doing this for a context manager that accepts resource "
"acquisition and release functions, along with an optional validation "
"function, and maps them to the context management protocol::"
msgstr ""
#: ../../library/contextlib.rst:759
msgid "Replacing any use of ``try-finally`` and flag variables"
msgstr ""
#: ../../library/contextlib.rst:761
msgid ""
"A pattern you will sometimes see is a ``try-finally`` statement with a flag "
"variable to indicate whether or not the body of the ``finally`` clause "
"should be executed. In its simplest form (that can't already be handled just "
"by using an ``except`` clause instead), it looks something like this::"
msgstr ""
#: ../../library/contextlib.rst:775
msgid ""
"As with any ``try`` statement based code, this can cause problems for "
"development and review, because the setup code and the cleanup code can end "
"up being separated by arbitrarily long sections of code."
msgstr ""
#: ../../library/contextlib.rst:779
msgid ""
":class:`ExitStack` makes it possible to instead register a callback for "
"execution at the end of a ``with`` statement, and then later decide to skip "
"executing that callback::"
msgstr ""
#: ../../library/contextlib.rst:791
msgid ""
"This allows the intended cleanup up behaviour to be made explicit up front, "
"rather than requiring a separate flag variable."
msgstr ""
#: ../../library/contextlib.rst:794
msgid ""
"If a particular application uses this pattern a lot, it can be simplified "
"even further by means of a small helper class::"
msgstr ""
#: ../../library/contextlib.rst:812
msgid ""
"If the resource cleanup isn't already neatly bundled into a standalone "
"function, then it is still possible to use the decorator form of :meth:"
"`ExitStack.callback` to declare the resource cleanup in advance::"
msgstr ""
#: ../../library/contextlib.rst:827
msgid ""
"Due to the way the decorator protocol works, a callback function declared "
"this way cannot take any parameters. Instead, any resources to be released "
"must be accessed as closure variables."
msgstr ""
#: ../../library/contextlib.rst:833
msgid "Using a context manager as a function decorator"
msgstr ""
#: ../../library/contextlib.rst:835
msgid ""
":class:`ContextDecorator` makes it possible to use a context manager in both "
"an ordinary ``with`` statement and also as a function decorator."
msgstr ""
#: ../../library/contextlib.rst:838
msgid ""
"For example, it is sometimes useful to wrap functions or groups of "
"statements with a logger that can track the time of entry and time of exit. "
"Rather than writing both a function decorator and a context manager for the "
"task, inheriting from :class:`ContextDecorator` provides both capabilities "
"in a single definition::"
msgstr ""
#: ../../library/contextlib.rst:859
msgid "Instances of this class can be used as both a context manager::"
msgstr ""
#: ../../library/contextlib.rst:865
msgid "And also as a function decorator::"
msgstr ""
#: ../../library/contextlib.rst:872
msgid ""
"Note that there is one additional limitation when using context managers as "
"function decorators: there's no way to access the return value of :meth:"
"`__enter__`. If that value is needed, then it is still necessary to use an "
"explicit ``with`` statement."
msgstr ""
#: ../../library/contextlib.rst:880
msgid ":pep:`343` - The \"with\" statement"
msgstr ":pep:`343` - \"with\" 陳述式"
#: ../../library/contextlib.rst:880
msgid ""
"The specification, background, and examples for the Python :keyword:`with` "
"statement."
msgstr ""
#: ../../library/contextlib.rst:886
msgid "Single use, reusable and reentrant context managers"
msgstr ""
#: ../../library/contextlib.rst:888
msgid ""
"Most context managers are written in a way that means they can only be used "
"effectively in a :keyword:`with` statement once. These single use context "
"managers must be created afresh each time they're used - attempting to use "
"them a second time will trigger an exception or otherwise not work correctly."
msgstr ""
#: ../../library/contextlib.rst:894
msgid ""
"This common limitation means that it is generally advisable to create "
"context managers directly in the header of the :keyword:`with` statement "
"where they are used (as shown in all of the usage examples above)."
msgstr ""
#: ../../library/contextlib.rst:898
msgid ""
"Files are an example of effectively single use context managers, since the "
"first :keyword:`with` statement will close the file, preventing any further "
"IO operations using that file object."
msgstr ""
#: ../../library/contextlib.rst:902
msgid ""
"Context managers created using :func:`contextmanager` are also single use "
"context managers, and will complain about the underlying generator failing "
"to yield if an attempt is made to use them a second time::"
msgstr ""
#: ../../library/contextlib.rst:930
msgid "Reentrant context managers"
msgstr ""
#: ../../library/contextlib.rst:932
msgid ""
"More sophisticated context managers may be \"reentrant\". These context "
"managers can not only be used in multiple :keyword:`with` statements, but "
"may also be used *inside* a :keyword:`!with` statement that is already using "
"the same context manager."
msgstr ""
#: ../../library/contextlib.rst:937
msgid ""
":class:`threading.RLock` is an example of a reentrant context manager, as "
"are :func:`suppress`, :func:`redirect_stdout`, and :func:`chdir`. Here's a "
"very simple example of reentrant use::"
msgstr ""
#: ../../library/contextlib.rst:956
msgid ""
"Real world examples of reentrancy are more likely to involve multiple "
"functions calling each other and hence be far more complicated than this "
"example."
msgstr ""
#: ../../library/contextlib.rst:960
msgid ""
"Note also that being reentrant is *not* the same thing as being thread "
"safe. :func:`redirect_stdout`, for example, is definitely not thread safe, "
"as it makes a global modification to the system state by binding :data:`sys."
"stdout` to a different stream."
msgstr ""
#: ../../library/contextlib.rst:969
msgid "Reusable context managers"
msgstr ""
#: ../../library/contextlib.rst:971
msgid ""
"Distinct from both single use and reentrant context managers are "
"\"reusable\" context managers (or, to be completely explicit, \"reusable, "
"but not reentrant\" context managers, since reentrant context managers are "
"also reusable). These context managers support being used multiple times, "
"but will fail (or otherwise not work correctly) if the specific context "
"manager instance has already been used in a containing with statement."
msgstr ""
#: ../../library/contextlib.rst:978
msgid ""
":class:`threading.Lock` is an example of a reusable, but not reentrant, "
"context manager (for a reentrant lock, it is necessary to use :class:"
"`threading.RLock` instead)."
msgstr ""
#: ../../library/contextlib.rst:982
msgid ""
"Another example of a reusable, but not reentrant, context manager is :class:"
"`ExitStack`, as it invokes *all* currently registered callbacks when leaving "
"any with statement, regardless of where those callbacks were added::"
msgstr ""
#: ../../library/contextlib.rst:1013
msgid ""
"As the output from the example shows, reusing a single stack object across "
"multiple with statements works correctly, but attempting to nest them will "
"cause the stack to be cleared at the end of the innermost with statement, "
"which is unlikely to be desirable behaviour."
msgstr ""
#: ../../library/contextlib.rst:1018
msgid ""
"Using separate :class:`ExitStack` instances instead of reusing a single "
"instance avoids that problem::"
msgstr ""