How can I represent an 'Enum' in Python?

Answer 1

def M_add_class_attribs(attribs):
    def foo(name, bases, dict_):
        for v, k in attribs:
            dict_[k] = v
        return type(name, bases, dict_)
    return foo

def enum(*names):
    class Foo(object):
        __metaclass__ = M_add_class_attribs(enumerate(names))
        def __setattr__(self, name, value):  # this makes it read-only
            raise NotImplementedError
    return Foo()

Use it like this:

Animal = enum('DOG', 'CAT')
Animal.DOG # returns 0
Animal.CAT # returns 1
Animal.DOG = 2 # raises NotImplementedError

if you just want unique symbols and don't care about the values, replace this line:

__metaclass__ = M_add_class_attribs(enumerate(names))

with this:

__metaclass__ = M_add_class_attribs((object(), name) for name in names)