Mypy doesn't understand class

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#4,177 opened on Oct 28, 2017 8 comments 22 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 45/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Stale
Tech stack: python
Domain: devtools

Research direction

Reproduce the report using the Python example in x.py and run mypy to confirm the undefined class error. Trace the type checker's name resolution for class, then add a regression test showing that it is understood as Foo and verify the test suite passes.

Written by the indexing model from the issue text.

Description

feature priority-2-low

Consider the following (Python 3, of course)

from typing import Any

class Foo:
    def foo(self, x:Any) -> bool:
        return isinstance(x, __class__)

mypy gives the following error:

x.py:5: error: Name '__class__' is not defined

It should assume __class__ to be Foo (as per the language documentation).

I usually work around this by adding

if TYPE_CHECKING:
    __class__ : Type

at the top of files that use __class__, but that's not ideal.

Dominant language: Python
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Merged PRs (30d): 54

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Mypy doesn't understand __class__