Enum Mixins

enum_mixins is a small Python package of mixins for adding practical behavior to enum and flag classes, especially aenum.Flag.

The package is pre-alpha and intentionally narrow: it provides runtime validation helpers, type-friendly flag iteration, non-null flag behavior, and custom names for combined flag values.

What It Provides

• IterableFlagMixin: keeps aenum.Flag values iterable while giving the iterator a useful type hint, and includes a helper for OR-ing a non-empty list of flags into one combined flag value.
• ValidatableEnumMixin: adds validate(key), which accepts only values that are instances of the enum class.
• ValidatableFlagMixin: adds validate_single_value(key), which rejects combined flag values such as Color.RED | Color.BLUE.
• NonNullableFlagMixin: rejects zero/null aenum.Flag values produced at runtime, such as Color(0) or operations whose result is zero.
• CustomNameSeparatorFlagMixin: customizes the separator used in generated names for combined aenum.Flag values, for example RED_BLUE instead of RED|BLUE.

Installation

pip install enum_mixins

The package requires Python 3.8 or newer and depends on aenum and typing-extensions.

For local development:

pip install -r requirements_dev.txt
pip install -e .
make test
make lint

Usage

Place mixins before aenum.Flag in the class bases:

import aenum
from enum_mixins import (
    CustomNameSeparatorFlagMixin,
    IterableFlagMixin,
    NonNullableFlagMixin,
    ValidatableFlagMixin,
)


class Color(
    IterableFlagMixin,
    ValidatableFlagMixin,
    NonNullableFlagMixin,
    CustomNameSeparatorFlagMixin,
    aenum.Flag,
):
    __default_separator__ = "_"

    RED = aenum.auto()
    BLUE = aenum.auto()
    GREEN = aenum.auto()
    MIXED = RED | GREEN


Color.validate(Color.RED)
Color.validate(Color.RED | Color.BLUE)

Color.validate_single_value(Color.RED)
# Color.validate_single_value(Color.RED | Color.BLUE) raises ValueError

(Color.RED | Color.BLUE).name
# "RED_BLUE"

list(Color.RED | Color.BLUE)
# [Color.RED, Color.BLUE]

Color(0)
# raises ValueError

CustomNameSeparatorFlagMixin only changes generated combined names. If a combined value is explicitly named in the enum, such as MIXED = RED | GREEN, the defined enum name is preserved.

Behavior Notes

The validation mixins work at runtime: validate() checks that the value is an instance of the enum class, and validate_single_value() additionally checks that exactly one flag is set. They do not parse strings or coerce external values into enum members.

NonNullableFlagMixin is intended for aenum.Flag. The current tests cover runtime zero-value rejection, but class-definition-time rejection of an explicit zero member is marked as expected-fail.

IterableFlagMixin.combine_flags_list_into_single_multiflag_value() uses functools.reduce, so it expects at least one flag in the list.

Project Status

Version 0.0.1 is marked as pre-alpha in the package metadata. The project is MIT licensed.

Changelog

0.0.1

• First release on PyPI.