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

Commencez par la section « Generator expressions » de la référence des expressions Python à l’URL de documentation indiquée, et comparez sa définition des expressions génératrices asynchrones avec l’exemple signalé de compréhension de liste asynchrone imbriquée. Clarifiez dans quels cas l’expression génératrice externe devient asynchrone, notamment la distinction avec une expression externe contenant une expression génératrice asynchrone. Consultez l’issue CPython correspondante, gh-138105, avant de continuer.