Special case Enum _generate_next_value_

Are you reporting a bug, or opening a feature request? Bug, I think :)

I'm trying to set up a convenience Enum subclass:

from enum import Enum
from typing import Any, List


class AutoNameEnum(Enum):
    def _generate_next_value_(name, start: int, count: int, last_values: List[Any]) -> str:  # noqa: N805
        return str(name).lower()

I would expect this to work since Enum is a core class, but mypy reports the following error:

Signature of "generate_next_value" incompatible with supertype "Enum"

It seems any typing of this signature leads to the same error. Typing name: str results in the previous error and

Self argument missing for a non-static method (or an invalid type for self)

while stripping all types instead results in the following error:

Function is missing a type annotation

What are the versions of mypy and Python you are using?

$ mypy --version
mypy 0.730
$ python --version
Python 3.6.8

What are the mypy flags you are using?

[mypy]
check_untyped_defs = true
disallow_any_generics = true
disallow_untyped_defs = true
follow_imports = skip
ignore_missing_imports = true
no_implicit_optional = true
warn_redundant_casts = true
warn_return_any = true
warn_unused_ignores = true

Workaround

def _generate_next_value_(  # type: ignore
    name: str, start: int, count: int, last_values: List[Any]  # noqa: N805
) -> str:
    return name.lower()

Maybe adding @staticmethod helps? Or move the helper out of the class (since it doesn't seem to have anything to do with the class)?

Oh wait, I didn't realize that you were overriding an internal API. But if @staticmethod works let's close this issue. (I think mypy was trying to tell you that. :-)

In Python 3.8, @staticmethod won't work.

from enum import Enum, auto
from typing import Any, List

class AutoNameEnum(Enum):
    @staticmethod
    def _generate_next_value_(
        name, start: int, count: int, last_values: List[Any]
    ) -> str:
        return str(name).lower()

    foo = auto()
    bar = auto()

results:

Traceback (most recent call last):
  File "auto_name_enum.py", line 5, in <module>
    class AutoNameEnum(Enum):
  File "auto_name_enum.py", line 12, in AutoNameEnum
    foo = auto()
  File "/Users/okumura/.pyenv/versions/3.8.1/lib/python3.8/enum.py", line 104, in __setitem__
    value.value = self._generate_next_value(key, 1, len(self._member_names), self._last_values[:])
TypeError: 'staticmethod' object is not callable

This problem bit me just now and the @staticmethod approach seems to work in Python 3.9.1 (no exception is being thrown).

@Venom1991

@Venom1991 @staticmethod doesn't seem to work in Python 3.9.15:

Run poetry run cdk deploy --all --require-approval never --strict --change-set-name "ci-${GITHUB_RUN_ID}"
  poetry run cdk deploy --all --require-approval never --strict --change-set-name "ci-${GITHUB_RUN_ID}"
  shell: /usr/bin/bash -e {0}
  env: […]
Traceback (most recent call last):
  File "/home/runner/work/geostore/geostore/app.py", line 7, in <module>
    from infrastructure.application_stack import Application
  File "/home/runner/work/geostore/geostore/infrastructure/application_stack.py", line 8, in <module>
    from .constructs.api import API
  File "/home/runner/work/geostore/geostore/infrastructure/constructs/api.py", line 18, in <module>
    from .table import Table
  File "/home/runner/work/geostore/geostore/infrastructure/constructs/table.py", line 6, in <module>
    from geostore.parameter_store import ParameterName
  File "/home/runner/work/geostore/geostore/geostore/parameter_store.py", line 24, in <module>
    class ParameterName(Enum):
  File "/home/runner/work/geostore/geostore/geostore/parameter_store.py", line 31, in ParameterName
    GIT_COMMIT = auto()
  File "/opt/hostedtoolcache/Python/3.9.15/x64/lib/python3.9/enum.py", line 142, in __setitem__
    value.value = self._generate_next_value(
TypeError: 'staticmethod' object is not callable

Subprocess exited with error 1
Error: Process completed with exit code 1.

Is this caused by python/cpython#86844?

Suppress type issue caused by bug

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Special case Enum _generate_next_value_ #7591

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Special case Enum _generate_next_value_ #7591

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gvanrossum commented on Oct 1, 2019

gvanrossum commented on Oct 1, 2019

kokumura commented on Jul 2, 2020

Venom1991 commented on Feb 17, 2021

l0b0 commented on Jan 10, 2023

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