Clarify that generator containing an async list comprehension becomes an async generator

Bug report

Bug description:

import asyncio


async def foo():
    print(x for x in [1])  # <generator object foo.<locals>.<genexpr> at 0x...>
    print([a async for a in b] for x in [1])  # <async_generator object foo.<locals>.<genexpr> at 0x...>


asyncio.run(foo())

This happens only if the genexp contains an async listcomp inside of it:

[snip]

This makes sense because the inner listcomp is async and therefore must be evaluated within an async context. It's not clearly documented, though: https://docs.python.org/3.14/reference/expressions.html#generator-expressions says "If a generator expression contains either async for clauses or await expressions it is called an asynchronous generator expression. An asynchronous generator expression returns a new asynchronous generator object, which is an asynchronous iterator (see Asynchronous Iterators)." However, I wouldn't necessarily expect that to include async for expressions in a nested scope. Also, when a genexp includes an async genexp, the outer genexp doesn't become async.

So I'd recommend that you open a CPython bug report to have this clarified in the documentation.

Originally posted by @JelleZijlstra in https://github.com/microsoft/pyright/discussions/10827#discussioncomment-14179632

CPython versions tested on:

3.13

Operating systems tested on:

No response

Linked PRs

• gh-138105

Beginne mit dem Abschnitt „Generator expressions“ in der Referenz zu Python-Ausdrücken unter der verlinkten Dokumentations-URL und vergleiche seine Definition von asynchronen Generatorausdrücken mit dem gemeldeten Beispiel einer verschachtelten asynchronen List-Comprehension. Kläre, wann der äußere Generatorausdruck asynchron wird, einschließlich der Unterscheidung zu einem äußeren Ausdruck, der einen asynchronen Generatorausdruck enthält. Prüfe das zugehörige CPython-Issue gh-138105, bevor du fortfährst.