[New-bugs-announce] [issue32162] typing.Generic breaks __init_subclass__

[Ilya Kulakov]

New submission from Ilya Kulakov <kulakov.ilya at gmail.com>:

When superclass inherits from Generic, attributes set for a subclass are incorrectly propagated to its superclass.

Without Generic attribute access raises an exception:

    class X:
        def __init_subclass__(cls, **kwargs):
            super().__init_subclass__(**kwargs)
            cls.attr = 42

    class Y(X):
        pass

    Y.attr  # 42
    X.attr  # AttributeError

With Generic it does not:

    import typing

    T = typing.TypeVar('T')

    class X(typing.Generic[T]):
        def __init_subclass__(cls, **kwargs):
            super().__init_subclass__(**kwargs)
            cls.attr = 42

    class Y(X):
        pass

    Y.attr  # 42
    X.attr  # 42

----------
messages: 307182
nosy: Ilya.Kulakov
priority: normal
severity: normal
status: open
title: typing.Generic breaks __init_subclass__
type: behavior
versions: Python 3.6

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32162>
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