8000 Old TypeVar and new [T:] annotations are not equivalent · Issue #17749 · python/mypy · GitHub
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Old TypeVar and new [T:] annotations are not equivalent #17749

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jolaf opened this issue Sep 8, 2024 · 4 comments
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Old TypeVar and new [T:] annotations are not equivalent #17749

jolaf opened this issue Sep 8, 2024 · 4 comments
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bug mypy got something wrong

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@jolaf
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jolaf commented Sep 8, 2024

Bug Report

If the same function is defined with old TypeVar syntax in one place and with new [T:] syntax in other place, mypy doesn't consider them equivalent.

To Reproduce

https://mypy-play.net/?mypy=1.11.2&python=3.12&enable-incomplete-feature=NewGenericSyntax&gist=78806d2f754ba0e5ce9bdcb61909fbc6
@jolaf jolaf added the bug mypy got something wrong label Sep 8, 2024
@erictraut
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Your two examples are different. In one case, you're defining a type variable with an upper bound (Callable[..., Any]) and in the other case, you're omitting the upper bound. Changing your sample to the following eliminates the type error:

    F = TypeVar("F", bound=Callable[..., Any])

@JelleZijlstra JelleZijlstra closed this as not planned Won't fix, can't repro, duplicate, stale Sep 8, 2024
@jolaf
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jolaf commented Sep 8, 2024 •
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Your two examples are different

Oh, I see now. Thanks!

But if that is so, it should probably be reflected in the output?

For now, the 'Redefinition' output is just missing, which is definitely wrong (bug number 1).
It becomes visible though if in the newer format type variable name is changed: https://mypy-play.net/?mypy=1.11.2&python=3.12&enable-incomplete-feature=NewGenericSyntax&gist=06224b5d473a6be86cae73f00e4643f1
And it looks like the types being compared are essentially identical, so it's difficult for a user to understand what's wrong and the situation looks like a mypy bug to a user.

For this not to be the case, bound= should be visible in the printout (bug number 2).

Should I file separate issues for thes 99F2 e?

@jolaf
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jolaf commented Sep 9, 2024

Or should we reopen this one?

@jolaf
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jolaf commented Sep 19, 2024

I've filed #17791 and #17792 to note the respective two bugs.

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