8000 Wrong stub for `fileinput.input()` · Issue #7922 · python/typeshed · GitHub
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Molkree opened this issue May 22, 2022 · 1 comment · Fixed by #7934
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Wrong stub for fileinput.input() #7922

Molkree opened this issue May 22, 2022 · 1 comment · Fixed by #7934

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@Molkree
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Molkree commented May 22, 2022

@JelleZijlstra:

the stubs appear to be wrong here:

typeshed/stdlib/fileinput.pyi

Line 32 in 6e18441

openhook: Callable[[StrOrBytesPath, str], IO[AnyStr]] = ...,

Only the openhook argument constrains the TypeVar, but it has a default, and if the argument is not given there's nothing for the type checker to use to decide on the value of the TypeVar. The typeshed stub should be changed to add a separate overload where openhook is not given.

microsoft/pyright#3494 (comment)
@AlexWaygood
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AlexWaygood commented May 22, 2022 •
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The stubs at the moment look quite buggy indeed! From my reading of the source code, I don't think it's actually the openhook parameter at all that determines whether the object returned is of type FileInput[str] or FileInput[bytes]. Instead, it's the value passed into the mode parameter. (You can see this by looking at the FileInput._readline method, which is called from FileInput.__next__.)

IO modes can be tricky to type in stub files, but it should be possible.

This was referenced May 23, 2022
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JelleZijlstra added a commit to JelleZijlstra/typeshed that referenced this issue May 24, 2022
@JelleZijlstra
fileinput: Fix TypeVar usage
860cd4a 
Fixes python#7922, part of python#7928.

Also discovered an apparent CPython bug in the process: python/cpython#93157
AlexWaygood pushed a commit that referenced this issue May 24, 2022
@JelleZijlstra
fileinput: Fix TypeVar usage (#7934)
d950ec3 
* fileinput: Fix TypeVar usage

Fixes #7922, part of #7928.
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fileinput: Fix TypeVar usage JelleZijlstra/typeshed
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@Molkree @AlexWaygood
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