Enum of enums in Python?

Question

Is it possible to have an enum of enums in Python? For example, I\'d like to have

enumA
    enumB
        elementA
        elementB
    enumC
        elementC
          


        

Answer 1

Note The below is interesting, and may be useful, but as @abarnert noted the resulting A Enum doesn't have Enum members -- i.e. list(A) returns an empty list.

---

Without commenting on whether an Enum of Enums is a good idea (I haven't yet decided ;) , this can be done... and with only a small amount of magic.

You can either use the Constant class from this answer:

class Constant:
    def __init__(self, value):
        self.value = value
    def __get__(self, *args):
        return self.value
    def __repr__(self):
        return '%s(%r)' % (self.__class__.__name__, self.value)

Or you can use the new aenum library and its built-in skip desriptor decorator (which is what I will show).

At any rate, by wrapping the subEnum classes in a descriptor they are sheltered from becoming members themselves.

Your example then looks like:

from aenum import Enum, skip

class enumA(Enum):
    @skip
    class enumB(Enum):
        elementA = 'a'
        elementB = 'b'
    @skip
    class enumC(Enum):
        elementC = 'c'
        elementD = 'd'

and you can then access them as:

print(enumA)
print(enumA.enumB)
print(enumA.enumC.elementD)

which gives you:

enumC.elementD

The difference between using Constant and skip is esoteric: in enumA's __dict__ 'enumB' will return a Constant object (if Constant was used) or if skip was used; normal access will always return .

In Python 3.5+ you can even (un)pickle the nested Enums:

print(pickle.loads(pickle.dumps(enumA.enumC.elementD)) is enumA.enumC.elementD)
# True

Do note that the subEnum doesn't include the parent Enum in it's display; if that's important I would suggest enhancing EnumMeta to recognize the Constant descriptor and modify its contained class' __repr__ -- but I'll leave that as an exercise for the reader. ;)