Enum implementation example

enum.py

class Unset(object):
    pass

class Item(object):
    _cnt = 0
    
    def __init__(self, value=Unset, choice=Unset):
        self.key = None
        self.value = value
        self.choice = choice
        self.num = Item._cnt
        Item._cnt += 1

class EnumMeta(type):
    def __new__(cls, name, bases, attrs):
        items = []
        for k, v in attrs.items():
            if isinstance(v, Item):
                v.key = k
                if v.value is Unset:
                    v.value = k.lower()
                if v.choice is Unset:
                    v.choice = k.capitalize()
                items.append(v)
                attrs[k] = v.value
        items.sort(key=lambda item: item.num)
        attrs['keys'] = [item.key for item in items]
        attrs['values'] = [item.value for item in items]
        if not 'choices' in attrs:
            attrs['choices'] = tuple((item.value, item.choice) for item in items)
        return super(EnumMeta, cls).__new__(cls, name, bases, attrs)

class Enum(object):
    __metaclass__ = EnumMeta
    
    @classmethod
    def url_re(cls):
        return '|'.join(str(v) for v in cls.values)

usage.py

import enum

class TrackAction(enum.Enum):
    PLAY  = enum.Item()
    STOP  = enum.Item(choice='Stop! Stop!')
    PAUSE = enum.Item(value='P')


print TrackAction.PLAY
# play

print TrackAction.STOP
# stop

print TrackAction.PAUSE
# P

print TrackAction.values
# ['play', 'stop', 'P']

print TrackAction.keys
# ['PLAY', 'STOP', 'PAUSE']

print TrackAction.choices
# (('play', 'Play'), ('stop', 'Stop! Stop!'), ('P', 'Pause'))

print r'^track/(?P<id>\d+)/(?P<event>'+TrackAction.url_re()+')/$'
# ^track/(?P<id>\d+)/(?P<event>play|stop|P)/$
# (can be used in urlconf)

Enum inheritance does not work.

>>> import enum

>>> class A(enum.Enum):
...     a = enum.Item()

class B(A):
...     b = enum.Item()

>>> assert len(B.values) == 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError

Thanks for your comment, Andrey.

You're right, inheritance doesn't work, it's just an example.
For now I'm happy with this naive implementation and not going to extend it.

But it's a good starting point from which anyone can fork and easily fix inheritance or add automatic numeric values generation or whatever he want :-)