Allow error codes to be disabled inline

[allanlewis]

Feature

I have some code like this:

flag = True
if flag:
    var: str = 'foo'
else:
    var: str = 'bar'

mypy complains about the redefinition of var:

foo.py:5: error: Name 'var' already defined on line 3

I would like mypy to not complain about this as long as the types are the same, or "compatible" by some definition.

Needless to say, the code within my if..else blocks is more complex than assigning a literal - in one case each branch has a try..except block, so I can't just use a ternary.

Pitch

The project I'm currently working on is a web app that uses feature flags. We therefore often have code blocks like the one above, and we would like mypy to not complain about this type of structure.

[JelleZijlstra]

As a workaround, you can put var: str above the if-else.

[allanlewis]

Thanks, @JelleZijlstra - that works for me.

[PeterJCLaw]

You can also skip the annotation on the second assignment:

flag = True
if flag:
    var: str = 'foo'
else:
    var = 'bar'

[terencehonles]

This seems to be a dupe of #6233 unless you want to describe how error codes should be disabled inline.

If you are not aware you can use # type: ignore and run with --show-error-codes in order to be more specific `# type: ignore[error-code]. You should also read what disabling the type checking does https://mypy.readthedocs.io/en/stable/common_issues.html#spurious-errors-and-locally-silencing-the-checker

[AlexWaygood]

This seems to be a dupe of #6233 unless you want to describe how error codes should be disabled inline.

I agree. I'm not sure exactly what's being proposed here.