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bpo-34793: Drop old-style context managers in asyncio.locks #17533

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merged 3 commits into from Feb 1, 2020

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@asvetlov
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asvetlov commented Dec 9, 2019

* ``with (await asyncio.lock):`` and ``with (yield from asyncio.lock):`` statements are
not longer supported, use ``async with lock`` instead. The same is correct for
``asyncio.Condition`` and ``asyncio.Semaphore``.
(Contributed by Andrew Svetlov in :issue:`34793`.)

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@1st1

1st1 Dec 9, 2019

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Please also replace the deprecation warning with changedversion in https://docs.python.org/3/library/asyncio-sync.html#boundedsemaphore

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asvetlov Dec 10, 2019

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Done



class _ContextManagerMixin:
def __enter__(self):
raise RuntimeError(
'"yield from" should be used as context manager expression')

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@1st1

1st1 Dec 9, 2019

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Should we keep this? We can change the error message to say that async with should be used...

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@asvetlov

asvetlov Dec 10, 2019

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I think the motivation was emphasizing that context managers were supported but in a slightly unusual way: with (yield from lock):; bare with lock: was forbidden.

After switching to async with lock: everything becomes clear: with is not supported in any form for the sake of async with. The error message is standard and well-known: AttributeError: __enter__. I think we shouldn't replace the default behavior.

Maybe the standard text can be improved globally, but it is another story, I guess.

asvetlov added 2 commits Dec 10, 2019
@asvetlov asvetlov merged commit 90d9ba6 into python:master Feb 1, 2020
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@asvetlov asvetlov deleted the asvetlov:drop-deprecations branch Feb 1, 2020
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