8000 Use `TypeIs` is for `iscoroutinefunction` by max-muoto · Pull Request #12148 · python/typeshed · GitHub
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Use TypeIs is for iscoroutinefunction #12148

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Use TypeIs is for iscoroutinefunction #12148

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max-muoto
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@max-muoto max-muoto commented Jun 17, 2024 •
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Use TypeIs for iscoroutinefunction to provide more accurate types in the negative case.

#8009 (comment) talks about former issues with the negative cases before TypeIs.

@max-muoto max-muoto marked this pull request as draft June 17, 2024 02:53
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Diff from mypy_primer, showing the effect of this PR on open source code:

aiohttp (https://github.com/aio-libs/aiohttp)
+ aiohttp/web_urldispatcher.py:183:14: error: Left operand of "and" is always true  [redundant-expr]
+ aiohttp/web_urldispatcher.py:183:14: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-redundant-expr for more info

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max-muoto commented Jun 17, 2024 •
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@JelleZijlstra It seems in this case:

if iscoroutinefunction(z):
    assert_type(z, Callable[[str, int], Coroutine[Any, Any, Any]])

The intersection type "(str, int) -> (str | Awaitable[bytes])" we now get is less accurate, since we know it's not awaitable. Curious if you have any thoughts or potential workarounds, since it would be a little bit of a regression.

Or perhaps it's just wroth the trade-off.

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This is incorrect because iscoroutinefunction() does not (and cannot) return True for all callables that return a Coroutine.

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This is incorrect because iscoroutinefunction() does not (and cannot) return True for all callables that return a Coroutine.

I see, closing this out then!

@max-muoto max-muoto closed this Jun 17, 2024
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jmehnle commented Aug 13, 2024

Eeeek, does this mean that despite TypeIs we still don't have a solution for totally narrowing types in if inspect.iscoroutinefunction(f): ... / else: ... constructs?

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