bpo-44963: Implement send() and throw() methods for anext_awaitable objects

[pablogsal]

https://bugs.python.org/issue44963

[pablogsal]

This does not cover the aclose() case.

[pablogsal]

~Actually, I don't know if this is the way we should handle this, because this allows to call send() multiple times to the wrapped generator, which is kinda wrong, as send() here applies to the anextawaitable object 😟 ~

Or maybe we are fine, is late here (someone should check) :(

Seems we are fine:

>>> async def blech():
...     yield 1
...     yield 2
...     yield 3
...
>>> x = blech()
>>> asend_obj = anext(x)
>>> asend_obj.send(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration: 1
>>> asend_obj.send(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: cannot reuse already awaited __anext__()/asend()
>>> asend_obj = anext(x)
>>> asend_obj.send(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration: 2
>>> asend_obj.send(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: cannot reuse already awaited __anext__()/asend()

[1st1]

Looks good to me. Although I'm not sure this is a blocker-level thing.

[1st1]

@pablogsal I'm still not sure about the semantics here. I need more time.

[bedevere-bot]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[1st1]

@pablogsal I think this is a go for merging.

[1st1]

@graingert Thomas, thanks for the thorough review.

[miss-islington]

Thanks @pablogsal for the PR 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

[bedevere-bot]

GH-28198 is a backport of this pull request to the 3.10 branch.

[pablogsal]

Thanks @1st1 for all the help and thanks @graingert for the reviews and the comments!