Return type of asyncio.gather with *args

[abionics]

There are some related issues:

• More precisely typehint asyncio.gather up to 5 params #1550
• Clarification: return type for asyncio.gather()? #3243
• Incorrect return type for asyncio.gather? #2652
• And several questions on StackOverflow

But the problem is still the same. When a generator is passed to asyncio.gather, the expected return type should be Future[list[_T]]. However, it currently returns Future[tuple[_T1]], leading to type hinting warnings. This is a common pattern in asyncio code, and every time it cause unnecessary warnings in IDEs

Example code snippet:

async def fetch(url: str) -> str:
    pass  # fetch logic


def analyze(responses: list[str]) -> int:
    pass  # analyze logic that need all responses, maybe external library


async def create_report(urls: list[str]):
    responses = await asyncio.gather(*(
        fetch(url)
        for url in urls
    ))
    some_value = analyze(responses)
    # create report

I read tasks.pyi file, but a significant number of developers use asyncio.gather(*[...]). So this behavior should be reviewed

Although practicality beats purity
(c) The Zen of Python

[JelleZijlstra]

Which type checker are you using? It seems to me that your code should match this overload:

typeshed/stdlib/asyncio/tasks.pyi

Line 145 in ad5ec92

def gather(*coros_or_futures: _FutureLike[_T], return_exceptions: Literal[False] = False) -> Future[list[_T]]: ... # type: ignore[overload-overlap]

which returns Future[list[_T]]. If your type checker instead picks the overload that returns a 1-tuple, then that should be fixed in the type checker.

I'll also rename this issue to be more focused.

[abionics]

I use PyCharm's built-in type checker. I run mypy and pyright type checkers on this code snippet and both return 0 errors. So it must be bug in PyCharm

@JelleZijlstra thank you! Your question was the answer :) I think you can close this issue