I've searched the Python documentation and the docs must be updated to explicitly state the necessity of aclose().

refs)
https://docs.python.org/3/reference/expressions.html#asynchronous-generator-functions
https://www.python.org/dev/peps/pep-0525/

I'm not sure that what the original authors' intention is, but for me, it looks like that calling aclose() is an optional thing and the responsibility to call aclose() on async generators is left to the asyncgen-shutdown handler of the event loop.

The example in this issue show that we need to aclose asyncgens whenever we are done with it, even far before shutting down the event loop.