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assignee='https://github.com/asvetlov'closed_at=<Date2019-09-17.13:20:51.172>created_at=<Date2019-09-03.00:13:42.963>labels= ['type-bug', '3.8', '3.9', 'release-blocker', '3.7', 'expert-asyncio']
title='AsyncGenerator breaks when not iterated fully with RuntimeError("can\'t send non-None value to a just-started coroutine")'updated_at=<Date2019-09-17.13:20:51.171>user='https://bugs.python.org/MichaelYoo'
# unhandled exception during asyncio.run() shutdown
# task: <Task finished coro=<<async_generator_athrow without __name__>()> exception=RuntimeError("can't send non-None value to a just-started coroutine")>
# RuntimeError: can't send non-None value to a just-started coroutine
There is a warning message that I don't expect to see. I would expect breaking from an async iteration to behave as if breaking from a normal iteration - that is, no problems.
However, I see the warning message shown above. Am I missing something? Otherwise, I believe this is a bug. Thanks!
I've added 'release blocker' priority to don't miss this bugfix for the next release.
Note that 3.7.5rc1 is scheduled to be tagged today so we need to make a decision on whether to hold the release for a fix. From a quick test, it looks like the behavior was introduced in 3.7.1 as the test does not fail for me with 3.7.0. If so, that seems to meet the criteria for a maintenance release regression and thus potentially a release blocker.