Overriding non-enumeration attributes in Enum subclass fails

[flaeppe]

Bug Report

Inheriting an Enum-class and overriding, for example, a dunder-attribute fails to typecheck. Although it works fine during runtime.

To Reproduce

from enum import Enum


class BaseEnum(Enum):
    __something__ = 3


class SomeEnum(BaseEnum):
    __something__ = 2

Expected Behavior

It should typecheck, as it passes during runtime.

Actual Behavior

error: Cannot override final attribute "__something__" (previously declared in base class "BaseEnum")

Your Environment

• Mypy version used: master (26fdd45)
• Mypy command-line flags: -
• Mypy configuration options from mypy.ini (and other config files):

strict_optional = True

• Python version used: 3.9.4
• Operating system and version: MacOS Catalina 10.15.6

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The issue has also been briefly mentioned in these places:

• 0.930 still gives me "inheriting final" error with an enum.Flag subclass #11850 (comment)
• Enum types cannot be inherited #10857 (comment)

[sobolevn]

@flaeppe are you interested in working on this? 🙂

[flaeppe]

I could take a swing at it if I find some time, though I'm not too familiar with mypy code so I'm not sure what'll come out of it.

If someone else feels like working on it, please go ahead