Coverage for /pythoncovmergedfiles/medio/medio/usr/lib/python3.9/contextlib.py: 2%
307 statements
« prev ^ index » next coverage.py v7.3.2, created at 2023-10-20 07:00 +0000
1"""Utilities for with-statement contexts. See PEP 343."""
2import abc
3import sys
4import _collections_abc
5from collections import deque
6from functools import wraps
7from types import MethodType, GenericAlias
9__all__ = ["asynccontextmanager", "contextmanager", "closing", "nullcontext",
10 "AbstractContextManager", "AbstractAsyncContextManager",
11 "AsyncExitStack", "ContextDecorator", "ExitStack",
12 "redirect_stdout", "redirect_stderr", "suppress"]
15class AbstractContextManager(abc.ABC):
17 """An abstract base class for context managers."""
19 __class_getitem__ = classmethod(GenericAlias)
21 def __enter__(self):
22 """Return `self` upon entering the runtime context."""
23 return self
25 @abc.abstractmethod
26 def __exit__(self, exc_type, exc_value, traceback):
27 """Raise any exception triggered within the runtime context."""
28 return None
30 @classmethod
31 def __subclasshook__(cls, C):
32 if cls is AbstractContextManager:
33 return _collections_abc._check_methods(C, "__enter__", "__exit__")
34 return NotImplemented
37class AbstractAsyncContextManager(abc.ABC):
39 """An abstract base class for asynchronous context managers."""
41 __class_getitem__ = classmethod(GenericAlias)
43 async def __aenter__(self):
44 """Return `self` upon entering the runtime context."""
45 return self
47 @abc.abstractmethod
48 async def __aexit__(self, exc_type, exc_value, traceback):
49 """Raise any exception triggered within the runtime context."""
50 return None
52 @classmethod
53 def __subclasshook__(cls, C):
54 if cls is AbstractAsyncContextManager:
55 return _collections_abc._check_methods(C, "__aenter__",
56 "__aexit__")
57 return NotImplemented
60class ContextDecorator(object):
61 "A base class or mixin that enables context managers to work as decorators."
63 def _recreate_cm(self):
64 """Return a recreated instance of self.
66 Allows an otherwise one-shot context manager like
67 _GeneratorContextManager to support use as
68 a decorator via implicit recreation.
70 This is a private interface just for _GeneratorContextManager.
71 See issue #11647 for details.
72 """
73 return self
75 def __call__(self, func):
76 @wraps(func)
77 def inner(*args, **kwds):
78 with self._recreate_cm():
79 return func(*args, **kwds)
80 return inner
83class _GeneratorContextManagerBase:
84 """Shared functionality for @contextmanager and @asynccontextmanager."""
86 def __init__(self, func, args, kwds):
87 self.gen = func(*args, **kwds)
88 self.func, self.args, self.kwds = func, args, kwds
89 # Issue 19330: ensure context manager instances have good docstrings
90 doc = getattr(func, "__doc__", None)
91 if doc is None:
92 doc = type(self).__doc__
93 self.__doc__ = doc
94 # Unfortunately, this still doesn't provide good help output when
95 # inspecting the created context manager instances, since pydoc
96 # currently bypasses the instance docstring and shows the docstring
97 # for the class instead.
98 # See http://bugs.python.org/issue19404 for more details.
101class _GeneratorContextManager(_GeneratorContextManagerBase,
102 AbstractContextManager,
103 ContextDecorator):
104 """Helper for @contextmanager decorator."""
106 def _recreate_cm(self):
107 # _GCM instances are one-shot context managers, so the
108 # CM must be recreated each time a decorated function is
109 # called
110 return self.__class__(self.func, self.args, self.kwds)
112 def __enter__(self):
113 # do not keep args and kwds alive unnecessarily
114 # they are only needed for recreation, which is not possible anymore
115 del self.args, self.kwds, self.func
116 try:
117 return next(self.gen)
118 except StopIteration:
119 raise RuntimeError("generator didn't yield") from None
121 def __exit__(self, type, value, traceback):
122 if type is None:
123 try:
124 next(self.gen)
125 except StopIteration:
126 return False
127 else:
128 raise RuntimeError("generator didn't stop")
129 else:
130 if value is None:
131 # Need to force instantiation so we can reliably
132 # tell if we get the same exception back
133 value = type()
134 try:
135 self.gen.throw(type, value, traceback)
136 except StopIteration as exc:
137 # Suppress StopIteration *unless* it's the same exception that
138 # was passed to throw(). This prevents a StopIteration
139 # raised inside the "with" statement from being suppressed.
140 return exc is not value
141 except RuntimeError as exc:
142 # Don't re-raise the passed in exception. (issue27122)
143 if exc is value:
144 return False
145 # Likewise, avoid suppressing if a StopIteration exception
146 # was passed to throw() and later wrapped into a RuntimeError
147 # (see PEP 479).
148 if type is StopIteration and exc.__cause__ is value:
149 return False
150 raise
151 except:
152 # only re-raise if it's *not* the exception that was
153 # passed to throw(), because __exit__() must not raise
154 # an exception unless __exit__() itself failed. But throw()
155 # has to raise the exception to signal propagation, so this
156 # fixes the impedance mismatch between the throw() protocol
157 # and the __exit__() protocol.
158 #
159 # This cannot use 'except BaseException as exc' (as in the
160 # async implementation) to maintain compatibility with
161 # Python 2, where old-style class exceptions are not caught
162 # by 'except BaseException'.
163 if sys.exc_info()[1] is value:
164 return False
165 raise
166 raise RuntimeError("generator didn't stop after throw()")
169class _AsyncGeneratorContextManager(_GeneratorContextManagerBase,
170 AbstractAsyncContextManager):
171 """Helper for @asynccontextmanager."""
173 async def __aenter__(self):
174 try:
175 return await self.gen.__anext__()
176 except StopAsyncIteration:
177 raise RuntimeError("generator didn't yield") from None
179 async def __aexit__(self, typ, value, traceback):
180 if typ is None:
181 try:
182 await self.gen.__anext__()
183 except StopAsyncIteration:
184 return
185 else:
186 raise RuntimeError("generator didn't stop")
187 else:
188 if value is None:
189 value = typ()
190 # See _GeneratorContextManager.__exit__ for comments on subtleties
191 # in this implementation
192 try:
193 await self.gen.athrow(typ, value, traceback)
194 raise RuntimeError("generator didn't stop after athrow()")
195 except StopAsyncIteration as exc:
196 return exc is not value
197 except RuntimeError as exc:
198 if exc is value:
199 return False
200 # Avoid suppressing if a StopIteration exception
201 # was passed to throw() and later wrapped into a RuntimeError
202 # (see PEP 479 for sync generators; async generators also
203 # have this behavior). But do this only if the exception wrapped
204 # by the RuntimeError is actully Stop(Async)Iteration (see
205 # issue29692).
206 if isinstance(value, (StopIteration, StopAsyncIteration)):
207 if exc.__cause__ is value:
208 return False
209 raise
210 except BaseException as exc:
211 if exc is not value:
212 raise
215def contextmanager(func):
216 """@contextmanager decorator.
218 Typical usage:
220 @contextmanager
221 def some_generator(<arguments>):
222 <setup>
223 try:
224 yield <value>
225 finally:
226 <cleanup>
228 This makes this:
230 with some_generator(<arguments>) as <variable>:
231 <body>
233 equivalent to this:
235 <setup>
236 try:
237 <variable> = <value>
238 <body>
239 finally:
240 <cleanup>
241 """
242 @wraps(func)
243 def helper(*args, **kwds):
244 return _GeneratorContextManager(func, args, kwds)
245 return helper
248def asynccontextmanager(func):
249 """@asynccontextmanager decorator.
251 Typical usage:
253 @asynccontextmanager
254 async def some_async_generator(<arguments>):
255 <setup>
256 try:
257 yield <value>
258 finally:
259 <cleanup>
261 This makes this:
263 async with some_async_generator(<arguments>) as <variable>:
264 <body>
266 equivalent to this:
268 <setup>
269 try:
270 <variable> = <value>
271 <body>
272 finally:
273 <cleanup>
274 """
275 @wraps(func)
276 def helper(*args, **kwds):
277 return _AsyncGeneratorContextManager(func, args, kwds)
278 return helper
281class closing(AbstractContextManager):
282 """Context to automatically close something at the end of a block.
284 Code like this:
286 with closing(<module>.open(<arguments>)) as f:
287 <block>
289 is equivalent to this:
291 f = <module>.open(<arguments>)
292 try:
293 <block>
294 finally:
295 f.close()
297 """
298 def __init__(self, thing):
299 self.thing = thing
300 def __enter__(self):
301 return self.thing
302 def __exit__(self, *exc_info):
303 self.thing.close()
306class _RedirectStream(AbstractContextManager):
308 _stream = None
310 def __init__(self, new_target):
311 self._new_target = new_target
312 # We use a list of old targets to make this CM re-entrant
313 self._old_targets = []
315 def __enter__(self):
316 self._old_targets.append(getattr(sys, self._stream))
317 setattr(sys, self._stream, self._new_target)
318 return self._new_target
320 def __exit__(self, exctype, excinst, exctb):
321 setattr(sys, self._stream, self._old_targets.pop())
324class redirect_stdout(_RedirectStream):
325 """Context manager for temporarily redirecting stdout to another file.
327 # How to send help() to stderr
328 with redirect_stdout(sys.stderr):
329 help(dir)
331 # How to write help() to a file
332 with open('help.txt', 'w') as f:
333 with redirect_stdout(f):
334 help(pow)
335 """
337 _stream = "stdout"
340class redirect_stderr(_RedirectStream):
341 """Context manager for temporarily redirecting stderr to another file."""
343 _stream = "stderr"
346class suppress(AbstractContextManager):
347 """Context manager to suppress specified exceptions
349 After the exception is suppressed, execution proceeds with the next
350 statement following the with statement.
352 with suppress(FileNotFoundError):
353 os.remove(somefile)
354 # Execution still resumes here if the file was already removed
355 """
357 def __init__(self, *exceptions):
358 self._exceptions = exceptions
360 def __enter__(self):
361 pass
363 def __exit__(self, exctype, excinst, exctb):
364 # Unlike isinstance and issubclass, CPython exception handling
365 # currently only looks at the concrete type hierarchy (ignoring
366 # the instance and subclass checking hooks). While Guido considers
367 # that a bug rather than a feature, it's a fairly hard one to fix
368 # due to various internal implementation details. suppress provides
369 # the simpler issubclass based semantics, rather than trying to
370 # exactly reproduce the limitations of the CPython interpreter.
371 #
372 # See http://bugs.python.org/issue12029 for more details
373 return exctype is not None and issubclass(exctype, self._exceptions)
376class _BaseExitStack:
377 """A base class for ExitStack and AsyncExitStack."""
379 @staticmethod
380 def _create_exit_wrapper(cm, cm_exit):
381 return MethodType(cm_exit, cm)
383 @staticmethod
384 def _create_cb_wrapper(callback, /, *args, **kwds):
385 def _exit_wrapper(exc_type, exc, tb):
386 callback(*args, **kwds)
387 return _exit_wrapper
389 def __init__(self):
390 self._exit_callbacks = deque()
392 def pop_all(self):
393 """Preserve the context stack by transferring it to a new instance."""
394 new_stack = type(self)()
395 new_stack._exit_callbacks = self._exit_callbacks
396 self._exit_callbacks = deque()
397 return new_stack
399 def push(self, exit):
400 """Registers a callback with the standard __exit__ method signature.
402 Can suppress exceptions the same way __exit__ method can.
403 Also accepts any object with an __exit__ method (registering a call
404 to the method instead of the object itself).
405 """
406 # We use an unbound method rather than a bound method to follow
407 # the standard lookup behaviour for special methods.
408 _cb_type = type(exit)
410 try:
411 exit_method = _cb_type.__exit__
412 except AttributeError:
413 # Not a context manager, so assume it's a callable.
414 self._push_exit_callback(exit)
415 else:
416 self._push_cm_exit(exit, exit_method)
417 return exit # Allow use as a decorator.
419 def enter_context(self, cm):
420 """Enters the supplied context manager.
422 If successful, also pushes its __exit__ method as a callback and
423 returns the result of the __enter__ method.
424 """
425 # We look up the special methods on the type to match the with
426 # statement.
427 _cm_type = type(cm)
428 _exit = _cm_type.__exit__
429 result = _cm_type.__enter__(cm)
430 self._push_cm_exit(cm, _exit)
431 return result
433 def callback(self, callback, /, *args, **kwds):
434 """Registers an arbitrary callback and arguments.
436 Cannot suppress exceptions.
437 """
438 _exit_wrapper = self._create_cb_wrapper(callback, *args, **kwds)
440 # We changed the signature, so using @wraps is not appropriate, but
441 # setting __wrapped__ may still help with introspection.
442 _exit_wrapper.__wrapped__ = callback
443 self._push_exit_callback(_exit_wrapper)
444 return callback # Allow use as a decorator
446 def _push_cm_exit(self, cm, cm_exit):
447 """Helper to correctly register callbacks to __exit__ methods."""
448 _exit_wrapper = self._create_exit_wrapper(cm, cm_exit)
449 self._push_exit_callback(_exit_wrapper, True)
451 def _push_exit_callback(self, callback, is_sync=True):
452 self._exit_callbacks.append((is_sync, callback))
455# Inspired by discussions on http://bugs.python.org/issue13585
456class ExitStack(_BaseExitStack, AbstractContextManager):
457 """Context manager for dynamic management of a stack of exit callbacks.
459 For example:
460 with ExitStack() as stack:
461 files = [stack.enter_context(open(fname)) for fname in filenames]
462 # All opened files will automatically be closed at the end of
463 # the with statement, even if attempts to open files later
464 # in the list raise an exception.
465 """
467 def __enter__(self):
468 return self
470 def __exit__(self, *exc_details):
471 received_exc = exc_details[0] is not None
473 # We manipulate the exception state so it behaves as though
474 # we were actually nesting multiple with statements
475 frame_exc = sys.exc_info()[1]
476 def _fix_exception_context(new_exc, old_exc):
477 # Context may not be correct, so find the end of the chain
478 while 1:
479 exc_context = new_exc.__context__
480 if exc_context is old_exc:
481 # Context is already set correctly (see issue 20317)
482 return
483 if exc_context is None or exc_context is frame_exc:
484 break
485 new_exc = exc_context
486 # Change the end of the chain to point to the exception
487 # we expect it to reference
488 new_exc.__context__ = old_exc
490 # Callbacks are invoked in LIFO order to match the behaviour of
491 # nested context managers
492 suppressed_exc = False
493 pending_raise = False
494 while self._exit_callbacks:
495 is_sync, cb = self._exit_callbacks.pop()
496 assert is_sync
497 try:
498 if cb(*exc_details):
499 suppressed_exc = True
500 pending_raise = False
501 exc_details = (None, None, None)
502 except:
503 new_exc_details = sys.exc_info()
504 # simulate the stack of exceptions by setting the context
505 _fix_exception_context(new_exc_details[1], exc_details[1])
506 pending_raise = True
507 exc_details = new_exc_details
508 if pending_raise:
509 try:
510 # bare "raise exc_details[1]" replaces our carefully
511 # set-up context
512 fixed_ctx = exc_details[1].__context__
513 raise exc_details[1]
514 except BaseException:
515 exc_details[1].__context__ = fixed_ctx
516 raise
517 return received_exc and suppressed_exc
519 def close(self):
520 """Immediately unwind the context stack."""
521 self.__exit__(None, None, None)
524# Inspired by discussions on https://bugs.python.org/issue29302
525class AsyncExitStack(_BaseExitStack, AbstractAsyncContextManager):
526 """Async context manager for dynamic management of a stack of exit
527 callbacks.
529 For example:
530 async with AsyncExitStack() as stack:
531 connections = [await stack.enter_async_context(get_connection())
532 for i in range(5)]
533 # All opened connections will automatically be released at the
534 # end of the async with statement, even if attempts to open a
535 # connection later in the list raise an exception.
536 """
538 @staticmethod
539 def _create_async_exit_wrapper(cm, cm_exit):
540 return MethodType(cm_exit, cm)
542 @staticmethod
543 def _create_async_cb_wrapper(callback, /, *args, **kwds):
544 async def _exit_wrapper(exc_type, exc, tb):
545 await callback(*args, **kwds)
546 return _exit_wrapper
548 async def enter_async_context(self, cm):
549 """Enters the supplied async context manager.
551 If successful, also pushes its __aexit__ method as a callback and
552 returns the result of the __aenter__ method.
553 """
554 _cm_type = type(cm)
555 _exit = _cm_type.__aexit__
556 result = await _cm_type.__aenter__(cm)
557 self._push_async_cm_exit(cm, _exit)
558 return result
560 def push_async_exit(self, exit):
561 """Registers a coroutine function with the standard __aexit__ method
562 signature.
564 Can suppress exceptions the same way __aexit__ method can.
565 Also accepts any object with an __aexit__ method (registering a call
566 to the method instead of the object itself).
567 """
568 _cb_type = type(exit)
569 try:
570 exit_method = _cb_type.__aexit__
571 except AttributeError:
572 # Not an async context manager, so assume it's a coroutine function
573 self._push_exit_callback(exit, False)
574 else:
575 self._push_async_cm_exit(exit, exit_method)
576 return exit # Allow use as a decorator
578 def push_async_callback(self, callback, /, *args, **kwds):
579 """Registers an arbitrary coroutine function and arguments.
581 Cannot suppress exceptions.
582 """
583 _exit_wrapper = self._create_async_cb_wrapper(callback, *args, **kwds)
585 # We changed the signature, so using @wraps is not appropriate, but
586 # setting __wrapped__ may still help with introspection.
587 _exit_wrapper.__wrapped__ = callback
588 self._push_exit_callback(_exit_wrapper, False)
589 return callback # Allow use as a decorator
591 async def aclose(self):
592 """Immediately unwind the context stack."""
593 await self.__aexit__(None, None, None)
595 def _push_async_cm_exit(self, cm, cm_exit):
596 """Helper to correctly register coroutine function to __aexit__
597 method."""
598 _exit_wrapper = self._create_async_exit_wrapper(cm, cm_exit)
599 self._push_exit_callback(_exit_wrapper, False)
601 async def __aenter__(self):
602 return self
604 async def __aexit__(self, *exc_details):
605 received_exc = exc_details[0] is not None
607 # We manipulate the exception state so it behaves as though
608 # we were actually nesting multiple with statements
609 frame_exc = sys.exc_info()[1]
610 def _fix_exception_context(new_exc, old_exc):
611 # Context may not be correct, so find the end of the chain
612 while 1:
613 exc_context = new_exc.__context__
614 if exc_context is old_exc:
615 # Context is already set correctly (see issue 20317)
616 return
617 if exc_context is None or exc_context is frame_exc:
618 break
619 new_exc = exc_context
620 # Change the end of the chain to point to the exception
621 # we expect it to reference
622 new_exc.__context__ = old_exc
624 # Callbacks are invoked in LIFO order to match the behaviour of
625 # nested context managers
626 suppressed_exc = False
627 pending_raise = False
628 while self._exit_callbacks:
629 is_sync, cb = self._exit_callbacks.pop()
630 try:
631 if is_sync:
632 cb_suppress = cb(*exc_details)
633 else:
634 cb_suppress = await cb(*exc_details)
636 if cb_suppress:
637 suppressed_exc = True
638 pending_raise = False
639 exc_details = (None, None, None)
640 except:
641 new_exc_details = sys.exc_info()
642 # simulate the stack of exceptions by setting the context
643 _fix_exception_context(new_exc_details[1], exc_details[1])
644 pending_raise = True
645 exc_details = new_exc_details
646 if pending_raise:
647 try:
648 # bare "raise exc_details[1]" replaces our carefully
649 # set-up context
650 fixed_ctx = exc_details[1].__context__
651 raise exc_details[1]
652 except BaseException:
653 exc_details[1].__context__ = fixed_ctx
654 raise
655 return received_exc and suppressed_exc
658class nullcontext(AbstractContextManager):
659 """Context manager that does no additional processing.
661 Used as a stand-in for a normal context manager, when a particular
662 block of code is only sometimes used with a normal context manager:
664 cm = optional_cm if condition else nullcontext()
665 with cm:
666 # Perform operation, using optional_cm if condition is True
667 """
669 def __init__(self, enter_result=None):
670 self.enter_result = enter_result
672 def __enter__(self):
673 return self.enter_result
675 def __exit__(self, *excinfo):
676 pass