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

從連結文件 URL 中 Python 表達式參考的「Generator expressions」章節開始，並將其中對非同步生成器表達式的定義與回報的巢狀非同步列表推導式範例進行比較。釐清外層生成器表達式何時會變成非同步，包括它與包含非同步生成器表達式的外層表達式之間的差異。在繼續之前，檢查相關的 CPython issue gh-138105。