8000 Enum final checking false positive in complex case · Issue #11702 · python/mypy · GitHub
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Enum final checking false positive in complex case #11702

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JukkaL opened this issue Dec 10, 2021 · 3 comments
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Enum final checking false positive in complex case #11702

JukkaL opened this issue Dec 10, 2021 · 3 comments
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bug mypy got something wrong false-positive mypy gave an error on correct code priority-0-high

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@JukkaL
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JukkaL commented Dec 10, 2021

This code generates a false positive, but weirdly I can only reproduce it if the base class is defined in a different module:

from mod import E

class EE(E):  # Cannot inherit from final class "E"
    X = (0, "")
# mod.py
from enum import Enum
from typing import Optional, Type

class E(int, Enum):
    def __init__(self, _: int, x: Optional[str] = None) -> None:
        self.x = x

    def __new__(cls: Type['E'], value: int, x: Optional[str] = None) -> 'E':
        enum = int.__new__(cls, value)
        enum._value_ = value
        enum.x = x
        return enum

The code works at runtime.

This started happening as a side effect of #11247.

Marking as high priority, since this is a regression. If it seems clear that this may only happen in pretty specialized circumstances, we can perhaps lower the priority.

cc @sobolevn
@JukkaL JukkaL added bug mypy got something wrong priority-0-high false-positive mypy gave an error on correct code labels Dec 10, 2021
@JukkaL JukkaL mentioned this issue Dec 10, 2021
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@sobolevn
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See https://github.com/python/mypy/pull/11579/files
Will it fix this case?

@sobolevn
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Looks like it fixes this issue indeed!
Снимок экрана 2021-12-10 в 20 35 04
Снимок экрана 2021-12-10 в 20 35 20

@JukkaL
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JukkaL commented Dec 10, 2021

Excellent! I can review the PR early next week.

@JukkaL JukkaL closed this as completed in 6de254e Dec 21, 2021
JukkaL pushed a commit that referenced this issue Dec 21, 2021
@sobolevn @JukkaL
Enums with annotations and no values are fine to be subclassed (#11579)
b31b06b 
Closes #11578. Closes #11702.
tushar-deepsource pushed a commit to DeepSourceCorp/mypy that referenced this issue Jan 20, 2022
@sobolevn @tushar-deepsource
Enums with annotations and no values are fine to be subclassed (pytho…
7f28792
55D4 
…n#11579)

Closes python#11578. Closes python#11702.
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