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[3.9] bpo-44566: resolve differences between asynccontextmanager and contextmanager (GH-27024). (#27269)

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(cherry picked from commit 7f1c330da3)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>
This commit is contained in:
Łukasz Langa 2021-07-20 21:12:58 +02:00 • committed by GitHub
parent dae4928dd0
commit 1c5c9c89ff
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4 changed files with 78 additions and 44 deletions
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85
Lib/contextlib.py
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@ -97,18 +97,20 @@ def __init__(self, func, args, kwds):
# for the class instead.
# See http://bugs.python.org/issue19404 for more details.
class _GeneratorContextManager(_GeneratorContextManagerBase,
AbstractContextManager,
ContextDecorator):
"""Helper for @contextmanager decorator."""
def _recreate_cm(self):
# _GCM instances are one-shot context managers, so the
# _GCMB instances are one-shot context managers, so the
# CM must be recreated each time a decorated function is
# called
return self.__class__(self.func, self.args, self.kwds)
class _GeneratorContextManager(
_GeneratorContextManagerBase,
AbstractContextManager,
ContextDecorator,
):
"""Helper for @contextmanager decorator."""
def __enter__(self):
# do not keep args and kwds alive unnecessarily
# they are only needed for recreation, which is not possible anymore
@ -118,8 +120,8 @@ def __enter__(self):
except StopIteration:
raise RuntimeError("generator didn't yield") from None
def __exit__(self, type, value, traceback):
if type is None:
def __exit__(self, typ, value, traceback):
if typ is None:
try:
next(self.gen)
except StopIteration:
@ -130,9 +132,9 @@ def __exit__(self, type, value, traceback):
if value is None:
# Need to force instantiation so we can reliably
# tell if we get the same exception back
value = type()
value = typ()
try:
self.gen.throw(type, value, traceback)
self.gen.throw(typ, value, traceback)
except StopIteration as exc:
# Suppress StopIteration *unless* it's the same exception that
# was passed to throw(). This prevents a StopIteration
@ -142,35 +144,39 @@ def __exit__(self, type, value, traceback):
# Don't re-raise the passed in exception. (issue27122)
if exc is value:
return False
# Likewise, avoid suppressing if a StopIteration exception
# Avoid suppressing if a StopIteration exception
# was passed to throw() and later wrapped into a RuntimeError
# (see PEP 479).
if type is StopIteration and exc.__cause__ is value:
# (see PEP 479 for sync generators; async generators also
# have this behavior). But do this only if the exception wrapped
# by the RuntimeError is actually Stop(Async)Iteration (see
# issue29692).
if (
isinstance(value, StopIteration)
and exc.__cause__ is value
):
return False
raise
except:
except BaseException as exc:
# only re-raise if it's *not* the exception that was
# passed to throw(), because __exit__() must not raise
# an exception unless __exit__() itself failed. But throw()
# has to raise the exception to signal propagation, so this
# fixes the impedance mismatch between the throw() protocol
# and the __exit__() protocol.
#
# This cannot use 'except BaseException as exc' (as in the
# async implementation) to maintain compatibility with
# Python 2, where old-style class exceptions are not caught
# by 'except BaseException'.
if sys.exc_info()[1] is value:
return False
raise
if exc is not value:
raise
return False
raise RuntimeError("generator didn't stop after throw()")
class _AsyncGeneratorContextManager(_GeneratorContextManagerBase,
AbstractAsyncContextManager):
"""Helper for @asynccontextmanager."""
"""Helper for @asynccontextmanager decorator."""
async def __aenter__(self):
# do not keep args and kwds alive unnecessarily
# they are only needed for recreation, which is not possible anymore
del self.args, self.kwds, self.func
try:
return await self.gen.__anext__()
except StopAsyncIteration:
@ -181,35 +187,48 @@ async def __aexit__(self, typ, value, traceback):
try:
await self.gen.__anext__()
except StopAsyncIteration:
return
return False
else:
raise RuntimeError("generator didn't stop")
else:
if value is None:
# Need to force instantiation so we can reliably
# tell if we get the same exception back
value = typ()
# See _GeneratorContextManager.__exit__ for comments on subtleties
# in this implementation
try:
await self.gen.athrow(typ, value, traceback)
raise RuntimeError("generator didn't stop after athrow()")
except StopAsyncIteration as exc:
# Suppress StopIteration *unless* it's the same exception that
# was passed to throw(). This prevents a StopIteration
# raised inside the "with" statement from being suppressed.
return exc is not value
except RuntimeError as exc:
# Don't re-raise the passed in exception. (issue27122)
if exc is value:
return False
# Avoid suppressing if a StopIteration exception
# was passed to throw() and later wrapped into a RuntimeError
# Avoid suppressing if a Stop(Async)Iteration exception
# was passed to athrow() and later wrapped into a RuntimeError
# (see PEP 479 for sync generators; async generators also
# have this behavior). But do this only if the exception wrapped
# by the RuntimeError is actully Stop(Async)Iteration (see
# issue29692).
if isinstance(value, (StopIteration, StopAsyncIteration)):
if exc.__cause__ is value:
return False
if (
isinstance(value, (StopIteration, StopAsyncIteration))
and exc.__cause__ is value
):
return False
raise
except BaseException as exc:
# only re-raise if it's *not* the exception that was
# passed to throw(), because __exit__() must not raise
# an exception unless __exit__() itself failed. But throw()
# has to raise the exception to signal propagation, so this
# fixes the impedance mismatch between the throw() protocol
# and the __exit__() protocol.
if exc is not value:
raise
return False
raise RuntimeError("generator didn't stop after athrow()")
def contextmanager(func):