Question

I started with this code snippet, which, by my understanding, is essentially a class-factory of sorts to emulate an “enum” type from other languages:

def enum(*sequential, **named):
    enums = dict(zip(sequential, range(len(sequential))), **named)
    return type('Enum', (), enums)

(which I took from here: How can I represent an 'Enum' in Python? )

I get how it works, and it does, but I would like to make my dynamically generated classes, which are of type ‘Enum’, iterable so that i can do the following in order to do a sanity check:

MyEnum = enum('FOO', 'BAR', 'JIMMY')
def func(my_enum_value):  # expects one of the MyEnum values
    if not my_enum_value in MyEnum:
        raise SomeSortOfException

However, in order to make that sanity check work, I need to make MyEnum iterable. I read here: http://pydanny.blogspot.com/2007/10/required-methods-to-make-class-iterable.html that I needed to add iter len contains and getitem methods to something in order to make it iterable. I started down this road (rewriting the enum code) but got stuck:

def enum(*sequential, **named):
    enums = dict(zip(sequential, range(len(sequential))), **named)
    enums['_enums'] = enums.copy() # (so I'd have them in the Class in order to use for the methods I'll be implementing to make it iterable)
    Enum = type('Enum', (), enums)

    Enum.__iter__ = #Er, how do I do this? Guess I'll ask SO
    Enum.__len__ =  # etc. 
    # . . . 
    return Enum

SO, how do I make my generated Enum classes iterable so I can use the ‘in’ word with them? This isn’t life or death for me, but I’m learning a ton of Python by doing this.

Answer 1

Use a smarter metaclass than type.

class EnumMC(type):
  def __contains__(self, val):
    return val in self.__dict__

def enum(*sequential, **named):
  enums = dict(zip(sequential, range(len(sequential))), **named)
  return EnumMC('Enum', (), enums)

MyEnum = enum('FOO', 'BAR', 'JIMMY')
def func(my_enum_value):  # expects one of the MyEnum values
    if not my_enum_value in MyEnum:
        raise ValueError()

func('FOO')
func('QUUX')

You may want to use an actual attribute to store the enum keys rather than depending on the class dictionary though.