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bpo-29679: Implement @contextlib.asynccontextmanager #360

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Merged
1st1 merged 18 commits into from
May 1, 2017
Merged

bpo-29679: Implement @contextlib.asynccontextmanager #360

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904e8a8
implement @asynccontextmanager
JelleZijlstra Jan 19, 2017
b3d59f1
add it to __all__
JelleZijlstra Feb 28, 2017
a1d5b3f
add tests (duplicating the @contextmanager ones)
JelleZijlstra Feb 28, 2017
c5b8b43
add docs
JelleZijlstra Mar 1, 2017
ca77cd2
back out ContextDecorator for asynccontextmanager (it doesn't work); …
JelleZijlstra Mar 1, 2017
689f4a5
move asynccontextmanager tests into their own file
JelleZijlstra Mar 1, 2017
299d968
fix when tests are run after test_asyncio
JelleZijlstra Mar 2, 2017
e974d48
add a few more tests
JelleZijlstra Mar 2, 2017
5808a4c
combine duplicate tests
JelleZijlstra Mar 2, 2017
9caa243
additional test for RuntimeError wrapping
JelleZijlstra Mar 2, 2017
64e6908
address 1st1's comments
JelleZijlstra Mar 2, 2017
178433b
clean up "except:" and explain why we can't do that for @contextmanager
JelleZijlstra Mar 3, 2017
6d0dddb
old-style classes, not strings
JelleZijlstra Mar 3, 2017
ad65b4d
add to whatsnew (and alphabetize modules)
JelleZijlstra Mar 3, 2017
737fd0f
add wraps decorator, add to docstring
JelleZijlstra Mar 3, 2017
3fc20a7
unalphabetize whatsnew
JelleZijlstra Mar 3, 2017
06697a8
Merge branch 'master' into asynccontextmanager
1st1 Mar 8, 2017
bb8de0d
Merge branch 'master' into asynccontextmanager
JelleZijlstra Apr 30, 2017
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additional test for RuntimeError wrapping
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@JelleZijlstra
JelleZijlstra committed Mar 2, 2017
commit 9caa2435a76836a9c7cf2b35f123e72e6186e297
11 changes: 9 additions & 2 deletions Lib/contextlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -163,8 +163,15 @@ async def __aexit__(self, type, value, traceback):
except RuntimeError as exc:
if exc is value:
return False
if exc.__cause__ is value:
return False
# Avoid suppressing if a StopIteration exception
# was passed to throw() 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
raise
except:
if sys.exc_info()[1] is not value:
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@1st1 1st1 Mar 2, 2017

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Why we use sys.exc_info() here instead of

except BaseException as exc:
    if exc is not value:
        raise

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@JelleZijlstra JelleZijlstra Mar 2, 2017

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I did this in order to not make unnecessary changes relative to the @contextmanager implementation, although I agree your code is better. I'm happy to change this if @ncoghlan is OK with it.

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@ncoghlan ncoghlan Mar 3, 2017

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It uses sys.exc_info() because the corresponding _GeneratorContextManager code predates the acceptance and implementation of PEP 352, and is also common between 2.7 and 3.x (and hence needs to handle exceptions that don't inherit from BaseException)

I'm fine with switching this to using the BaseException form, but add a comment to the synchronous version saying it's written that way on purpose to keep the code consistent with the 2.7 branch and the contextlib2 backport.

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20 changes: 20 additions & 0 deletions Lib/test/test_contextlib_async.py
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Expand Up @@ -139,6 +139,26 @@ async def woohoo():
else:
self.fail(f'{stop_exc} was suppressed')

@_async_test
async def test_contextmanager_wrap_runtimeerror(self):
@asynccontextmanager
async def woohoo():
try:
yield
except Exception as exc:
raise RuntimeError(f'caught {exc}') from exc

with self.assertRaises(RuntimeError):
async with woohoo():
1 / 0

# If the context manager wrapped StopAsyncIteration in a RuntimeError,
# we also unwrap it, because we can't tell whether the wrapping was
# done by the generator machinery or by the generator itself.
with self.assertRaises(StopAsyncIteration):
async with woohoo():
raise StopAsyncIteration

def _create_contextmanager_attribs(self):
def attribs(**kw):
def decorate(func):
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