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

从链接文档 URL 中 Python 表达式参考的“Generator expressions”部分开始，并将其中对异步生成器表达式的定义与报告的嵌套异步列表推导式示例进行比较。明确外层生成器表达式何时会变为异步，包括它与包含异步生成器表达式的外层表达式之间的区别。在继续之前，检查相关的 CPython issue gh-138105。