Add an asynchronous itertools implementation

[agronholm]

Things to check first

• I have searched the existing issues and didn't find my feature already requested there

Feature description

This would add an async counterpart for the itertools standard library module.

Use case

The need to iterate over async iterables is a fairly common one, and this is why aioitertools exists.

[11kkw]

I've been experimenting with an async counterpart to several itertools functions.

Before opening a PR, I'd like to check if the implementation direction makes
sense for AnyIO. If not, I'm happy to revise the implementation.

Any feedback would be appreciated.

[agronholm]

OK, which repo should I be looking at?

[11kkw]

OK, which repo should I be looking at?

You can take a look here:

https://github.com/11kkw/anyio/tree/feature/async-itertools-998

[agronholm]

It will take a while to get through this, but a couple things caught my eye:

• https://github.com/11kkw/anyio/blob/feature/async-itertools-998/src/anyio/_itertools.py#L482 <- what's with the cast?
• https://github.com/11kkw/anyio/blob/feature/async-itertools-998/src/anyio/_itertools.py#L481 <- use AsyncGenerator for the return type annotation so we can use async with aclosing(...) with it

[agronholm]

Overall I think this looks good. There will probably be a few more change requests, but I see no problem with sending a PR.

[11kkw]

Overall I think this looks good. There will probably be a few more change requests, but I see no problem with sending a PR.

You're right, that was a mistake. I'll fix it and open a PR. Thanks for reviewing.