Demonstrates extensible Integer Choice.

extensible-integer-choices.py

from django.db import models
from django.utils.functional import classproperty


class InheritableIntegerChoicesMeta(type):
    def __init__(cls, name, bases, attrs):
        super().__init__(name, bases, attrs)
        choices = []
        for c in cls.mro():
            choices += [(value, name) for name, value in c.__dict__.items() if not callable(value) and not name.startswith("__") and name != "choices"]
        cls.choices = classproperty(lambda cls: choices)


class InheritableIntegerChoices(metaclass=InheritableIntegerChoicesMeta):
    pass


class BaseChoices(InheritableIntegerChoices):
    NONE = 0


class SMSChannels(BaseChoices):
    SMS = 1


class EmailChannels(BaseChoices):
    EMAIL = 2


class SMSEmailChannels(SMSChannels, EmailChannels):
    SMS_EMAIL = 3


class MyModel(models.Model):
    category1 = models.PositiveIntegerField(
        choices=SMSEmailChannels.choices,
        default=SMSEmailChannels.SMS_EMAIL,
    )
    category2 = models.PositiveIntegerField(
        choices=SMSChannels.choices,
        default=SMSChannels.SMS,
    )