A task created with asyncio.shield() never retrieves the task exception, which results in a log message being generated. See the attached script for a minimal example. Output looks something like this:

<snip>
Task exception was never retrieved
future: <Task finished name='Task-2' coro=<some_coroutine() done, defined at /Users/natano/python-bug/trigger-warning.py:4> exception=Exception('foo')>
Traceback (most recent call last):
  File "/Users/natano/python-bug/trigger-warning.py", line 6, in some_coroutine
    raise Exception('foo')
Exception: foo
</snip>

I believe this behaviour is not intended and is an unintended side-effect of commit b35acc5b3a0148c5fd4462968b310fb436726d5a (https://github.com/python/cpython/commit/b35acc5b3a0148c5fd4462968b310fb436726d5a). The _inner_done_callback has has code to retrieve the exception when the outer task was cancelled, but since that commit the _inner_done_callback is not called anymore when the outer task was cancelled.


(Tested with 3.8, 3.9 and 3.10. I don't have a python 3.7 version available for testing, but I think this issue also affects 3.7.)

I'm not sure how to fix this, but here is a regression test for the issue. (failing on the current master branch)

Thanks for the report.

I didn't test but looks like `outer.exception()` call can suppress the message about not retrieved exception.

How would calling `outer.exception()` suppress the message? This happens when the outer task is cancelled while the inner task is still running. In that case the exception is never set on outer.