Always infer in operator as returning bool

[TV4Fun]

Resolves #5656

[TV4Fun]

Tangentially related: Is there a way to have the test suite do type checks on Mypy's own code?

[JelleZijlstra]

Does this mean that we won't check type errors within the subexpressions of the in expressions?

Concretely, does mypy still report an error on code like 1 in ([1] + ['x'])?

[TV4Fun]

The example you gave still produces an error, but just to be on the safe side, I've added some extra type checking, and a test to make sure this is still an error.

[JelleZijlstra]

We run a self-check (mypy typechecking itself) as part of the test suite.

[TV4Fun]

@JelleZijlstra, the reason I asked about type checking Mypy, is that before I submitted this PR, I ran the full test suite with pytest, but there was still a type error that was only caught by the CI build after I submitted.

[gvanrossum]

before I submitted this PR, I ran the full test suite with pytest, but there was still a type error that was only caught by the CI build after I submitted.

That's because CI does a bit more than just run pytest. Check out the contents of .travis.yml and appveyor.yml to see what.

You can type-check mypy with itself using something like python3 -m mypy --config-file mypy_self_check.ini mypy.

[TV4Fun]

Thanks for that information @gvanrossum. I might suggest adding that to the documentation for tests to run before submitting a PR.

[gvanrossum]

It’s not the end of the world if CI fails. Just fix it and push again.

On Sun, Sep 30, 2018 at 12:34 PM Joel Croteau ***@***.***> wrote: Thanks for that information @gvanrossum <https://github.com/gvanrossum>. I might suggest adding that to the documentation for tests to run before submitting a PR. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#5688 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACwrMvzerI7bBxF-4SBM8lMyWLgi-jTPks5ugRzegaJpZM4W9wnA> .

-- --Guido (mobile)

[gvanrossum]

I forgot one thing. (It's also not in any README file.) There's a script runtests.py that runs all the tests, including the self tests. I was reminded of this by #5702.

[jonapich]

Am I seeing the same behavior with == operator?

    def __eq__(self, other: Any) -> bool:
        return other == self.value

warning: Returning Any from function declared to return "bool"

[ilevkivskyi]

@jonapich
No, you don't:

>>> class C:
...     def __eq__(self, other):
...         return 'surprise'
...     def __contains__(self, other):
...         return 'no way'
... 
>>> 1 in C()
True
>>> 1 == C()
'surprise'

[jonapich]

🙊

🏃‍♂️

[msullivan]

This seems solid to me. If you rebase and fix merge conflicts I think we can merge it.

[msullivan]

I went and rebased this and will merge it now