_asyncio._get_running_loop can return None

[jonathandung]

I recently found out the type checker I was using marked a branch where asyncio.events._get_running_loop returns None as unreachable. However, this simple snippet will show otherwise:

$ python -c "print(__import__('asyncio')._get_running_loop())"
None

None is returned when there is no running loop, as per the documentation:

$ python -m pydoc asyncio._get_running_loop
Help on built-in function _get_running_loop in asyncio:                                                                                                                        

asyncio._get_running_loop = _get_running_loop()
    Return the running event loop or None.

    This is a low-level function intended to be used by event loops.
    This function is thread-specific.

In the stubs, asyncio.events reexports _asyncio._get_running_loop, and the asyncio top level pulls that in. This thus affects all three locations where the symbol is available. Typing the return type as a union AbstractEventLoop | None fixes this.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉