How can I represent an 'Enum' in Python?

Answer 1

I really like Alec Thomas' solution (http://stackoverflow.com/a/1695250):

def enum(**enums):
    '''simple constant "enums"'''
    return type('Enum', (object,), enums)

It's elegant and clean looking, but it's just a function that creates a class with the specified attributes.

With a little modification to the function, we can get it to act a little more 'enumy':

NOTE: I created the following examples by trying to reproduce the behavior of pygtk's new style 'enums' (like Gtk.MessageType.WARNING)

def enum_base(t, **enums):
    '''enums with a base class'''
    T = type('Enum', (t,), {})
    for key,val in enums.items():
        setattr(T, key, T(val))

    return T

This creates an enum based off a specified type. In addition to giving attribute access like the previous function, it behaves as you would expect an Enum to with respect to types. It also inherits the base class.

For example, integer enums:

>>> Numbers = enum_base(int, ONE=1, TWO=2, THREE=3)
>>> Numbers.ONE
1
>>> x = Numbers.TWO
>>> 10 + x
12
>>> type(Numbers)

>>> type(Numbers.ONE)

>>> isinstance(x, Numbers)
True

Another interesting thing that can be done with this method is customize specific behavior by overriding built-in methods:

def enum_repr(t, **enums):
    '''enums with a base class and repr() output'''
    class Enum(t):
        def __repr__(self):
            return ''.format(self._name, t.__name__)

    for key,val in enums.items():
        i = Enum(val)
        i._name = key
        setattr(Enum, key, i)

    return Enum



>>> Numbers = enum_repr(int, ONE=1, TWO=2, THREE=3)
>>> repr(Numbers.ONE)
''
>>> str(Numbers.ONE)
'1'