Attribute resolution of an Enum member that is an instance of a subclass of the mixin class does not follow MRO

[blhsing]

Bug report

Bug description:

As reported in https://stackoverflow.com/questions/78120133/python-enum-of-classes-with-polymorphism .

Since the idea of a mixin class to an Enum is to make the members behave like instances of the mixin class, I think it's reasonable to expect that attribute resolution of a member whose value is an instance of a subclass of the mixin class follows MRO as well. Currently the attribute resolution appears to stick to the base mixin class.

Minimal reproducible example:

from enum import Enum

class Base:
    name = 'base'

class Child(Base):
    name = 'child'

class BaseEnum(Base, Enum):
    FOO = Child()

print(BaseEnum.FOO.name) # outputs 'base' when 'child' is expected
print(BaseEnum.FOO.value.name) # outputs 'child' as expected

CPython versions tested on:

3.12

Operating systems tested on:

Linux, Windows

[ethanfurman]

>>> isinstance(BaseEnum.FOO, Base)
True

>>> isinstance(BaseEnum.FOO, Child)
False

Child is not in BaseEnums mro.

[blhsing]

>>> isinstance(BaseEnum.FOO, Base)
True

>>> isinstance(BaseEnum.FOO, Child)
False

Child is not in BaseEnums mro.

Right. It isn't clear why the Activations class in the SO question needs to be an Enum at all in the first place, and I can't think of a good real-world use case myself. I simply concur with the OP of the SO question that the behavior is somewhat unexpected/counter-intuitive. That's all.

Just left a comment in the SO question requesting clarification.