Typing error when defining an enum of an attrs class

[MicaelJarniac]

When trying to define an enum of an @attrs.define class, Mypy gives typing errors, but it works in runtime.

When trying to define an enum of an @attrs.frozen class, Mypy doesn't give an error, but it errors at runtime.

When trying to define an enum of a @dataclasses.dataclass class, Mypy doesn't give an error, and it works at runtime.

I started noticing this today after I removed support for Python 3.9 from my project, and ran poetry update.

from dataclasses import dataclass
from enum import Enum

import attrs
from pytest import raises

@attrs.define
class AttrsDefine:
    a: int
    b: float

# error: Definition of "__hash__" in base class "AttrsDefine" is incompatible with definition in base class "Enum"  [misc]
class AttrsDefineEnum(AttrsDefine, Enum):
    X = (1, 2.0)
    Y = (3, 4.0)

@attrs.frozen
class AttrsFrozen:
    a: int
    b: float

@dataclass
class Dataclass:
    a: int
    b: float

class DataclassEnum(Dataclass, Enum):
    X = (1, 2.0)
    Y = (3, 4.0)

def test_enums() -> None:
    with raises(attrs.exceptions.FrozenInstanceError) as exc_info:

        # attr.exceptions.FrozenInstanceError
        class AttrsFrozenEnum(AttrsFrozen, Enum):
            X = (1, 2.0)
            Y = (3, 4.0)

        print(repr(AttrsFrozenEnum.X))

    print(exc_info.exconly())
    print(repr(AttrsDefineEnum.X))
    print(repr(DataclassEnum.X))

❯ mypy attrenum.py
attrenum.py:15: error: Definition of "__hash__" in base class "AttrsDefine" is incompatible with definition in base class "Enum"  [misc]
Found 1 error in 1 file (checked 1 source file)
❯ pytest -s attrenum.py
=================================================================================== test session starts ===================================================================================
platform linux -- Python 3.11.6, pytest-7.4.0, pluggy-1.2.0
rootdir: /home/micael/projects/playground
collected 1 item                                                                                                                                                                          

attrenum.py attr.exceptions.FrozenInstanceError
AttrsDefineEnum(a=1, b=2.0)
<DataclassEnum.X: Dataclass(a=1, b=2.0)>
.

==================================================================================== 1 passed in 0.01s ====================================================================================

❯ python --version
Python 3.11.4
❯ mypy --version
mypy 1.10.0 (compiled: yes)
❯ pip freeze
attrs==23.2.0
iniconfig==2.0.0
mypy==1.10.0
mypy-extensions==1.0.0
packaging==24.0
pluggy==1.5.0
pytest==8.2.1
typing_extensions==4.11.0

[hynek]

What about dataclass(frozen=True)? So far, it sounds a Mypy thing to me.

[MicaelJarniac]

from dataclasses import dataclass
from enum import Enum

import attrs
from pytest import raises

@attrs.define
class AttrsDefine:
    a: int
    b: float

# error: Definition of "__hash__" in base class "AttrsDefine" is incompatible with definition in base class "Enum"  [misc]
class AttrsDefineEnum(AttrsDefine, Enum):
    X = (1, 2.0)
    Y = (3, 4.0)

@attrs.frozen
class AttrsFrozen:
    a: int
    b: float

@dataclass
class Dataclass:
    a: int
    b: float

class DataclassEnum(Dataclass, Enum):
    X = (1, 2.0)
    Y = (3, 4.0)

@dataclass(frozen=True)
class DataclassFrozen:
    a: int
    b: float

class DataclassFrozenEnum(DataclassFrozen, Enum):
    X = (1, 2.0)
    Y = (3, 4.0)

def test_enums() -> None:
    with raises(attrs.exceptions.FrozenInstanceError) as exc_info:

        class AttrsFrozenEnum(AttrsFrozen, Enum):
            X = (1, 2.0)
            Y = (3, 4.0)

        print(repr(AttrsFrozenEnum.X))

    print(exc_info.exconly())  # attrenum.py attr.exceptions.FrozenInstanceError
    print(repr(AttrsDefineEnum.X))  # AttrsDefineEnum(a=1, b=2.0)
    print(repr(DataclassEnum.X))  # <DataclassEnum.X: a=1, b=2.0>
    print(repr(DataclassFrozenEnum.X))  # <DataclassFrozenEnum.X: a=1, b=2.0>

❯ mypy attrenum.py
attrenum.py:15: error: Definition of "__hash__" in base class "AttrsDefine" is incompatible with definition in base class "Enum"  [misc]
Found 1 error in 1 file (checked 1 source file)
❯ pytest -s attrenum.py
===================================================================================================================== test session starts =====================================================================================================================
platform linux -- Python 3.12.4, pytest-8.3.1, pluggy-1.5.0
rootdir: /home/micael/projects/playground
collected 1 item                                                                                                                                                                                                                                              

attrenum.py attr.exceptions.FrozenInstanceError
AttrsDefineEnum(a=1, b=2.0)
<DataclassEnum.X: a=1, b=2.0>
<DataclassFrozenEnum.X: a=1, b=2.0>
.

====================================================================================================================== 1 passed in 0.02s ======================================================================================================================