[Python-checkins] [3.9] bpo-44566: resolve differences between asynccontextmanager and contextmanager (GH-27024). (#27269)
ambv
webhook-mailer at python.org
Tue Jul 20 15:13:03 EDT 2021
https://github.com/python/cpython/commit/1c5c9c89ffc36875afaf4c3cc6a716d4bd089bbf
commit: 1c5c9c89ffc36875afaf4c3cc6a716d4bd089bbf
branch: 3.9
author: Łukasz Langa <lukasz at langa.pl>
committer: ambv <lukasz at langa.pl>
date: 2021-07-20T21:12:58+02:00
summary:
[3.9] bpo-44566: resolve differences between asynccontextmanager and contextmanager (GH-27024). (#27269)
(cherry picked from commit 7f1c330da31c54e028dceaf3610877914c2a4497)
Co-authored-by: Thomas Grainger <tagrain at gmail.com>
files:
A Misc/NEWS.d/next/Library/2021-07-05-18-13-25.bpo-44566.o51Bd1.rst
M Lib/contextlib.py
M Lib/test/test_contextlib.py
M Lib/test/test_contextlib_async.py
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index ff92d9f913f4c..f60f0c274a715 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -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):
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 024f912647295..ad071bb2a22d3 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -125,19 +125,22 @@ def woohoo():
self.assertEqual(state, [1, 42, 999])
def test_contextmanager_except_stopiter(self):
- stop_exc = StopIteration('spam')
@contextmanager
def woohoo():
yield
- try:
- with self.assertWarnsRegex(DeprecationWarning,
- "StopIteration"):
- with woohoo():
- raise stop_exc
- except Exception as ex:
- self.assertIs(ex, stop_exc)
- else:
- self.fail('StopIteration was suppressed')
+
+ class StopIterationSubclass(StopIteration):
+ pass
+
+ for stop_exc in (StopIteration('spam'), StopIterationSubclass('spam')):
+ with self.subTest(type=type(stop_exc)):
+ try:
+ with woohoo():
+ raise stop_exc
+ except Exception as ex:
+ self.assertIs(ex, stop_exc)
+ else:
+ self.fail(f'{stop_exc} was suppressed')
def test_contextmanager_except_pep479(self):
code = """\
diff --git a/Lib/test/test_contextlib_async.py b/Lib/test/test_contextlib_async.py
index 43fb7fced1bfd..9d6854c702892 100644
--- a/Lib/test/test_contextlib_async.py
+++ b/Lib/test/test_contextlib_async.py
@@ -207,7 +207,18 @@ async def test_contextmanager_except_stopiter(self):
async def woohoo():
yield
- for stop_exc in (StopIteration('spam'), StopAsyncIteration('ham')):
+ class StopIterationSubclass(StopIteration):
+ pass
+
+ class StopAsyncIterationSubclass(StopAsyncIteration):
+ pass
+
+ for stop_exc in (
+ StopIteration('spam'),
+ StopAsyncIteration('ham'),
+ StopIterationSubclass('spam'),
+ StopAsyncIterationSubclass('spam')
+ ):
with self.subTest(type=type(stop_exc)):
try:
async with woohoo():
diff --git a/Misc/NEWS.d/next/Library/2021-07-05-18-13-25.bpo-44566.o51Bd1.rst b/Misc/NEWS.d/next/Library/2021-07-05-18-13-25.bpo-44566.o51Bd1.rst
new file mode 100644
index 0000000000000..3b00a1b715fee
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-07-05-18-13-25.bpo-44566.o51Bd1.rst
@@ -0,0 +1 @@
+handle StopIteration subclass raised from @contextlib.contextmanager generator
\ No newline at end of file
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