Clarify enumeration types are true Python Enums

[johnthagen]

​https://docs.djangoproject.com/en/3.2/ref/models/fields/#field-choices-enum-types

I was originally hesitant to use the Django "enumeration fields" when I first read about them because to me the documentation made it sound like they were "similar" to Python Enums, but something different. I value using core data types for interop with other non-Django specific code, so I continued to use django-enumfields (​https://github.com/hzdg/django-enumfields) for several releases. This allowed me to use true Python Enums which are familiar to use to developers not as versed in Django.

Recently I dug into the Django source code more deeply after hearing about them again and discovered that indeed the Choices type is really just an Enum with a little extra magic and some extra helper methods applied to them (and as such can be used as a normal Python Enum as well).

class ChoicesMeta(enum.EnumMeta):
    """A metaclass for creating a enum choices."""

...

class Choices(enum.Enum, metaclass=ChoicesMeta):
    """Class for creating enumerated choices."""

I would recommend modifying the docs in some way, for example:

These work similar to enum from Python’s standard library, but with some modifications:

Could be reworded:

These are true Enums from Python's standard library, but with some additional extensions added:

[johnthagen]

Continuing some research, I learned that Django won't return an Enum instance from a field decorated using a Choices Enum (as described at the bottom of ​https://stackoverflow.com/a/58051918), unlike django-enumfields (​https://pypi.org/project/django-enumfields/). Since the user doesn't get an Enum instance back out directly, perhaps the way the docs are currently worded is in fact appropriate.

[Mariusz Felisiak]

Yeah, I think the current form is more appropriate.