Custom enum creation in Python [duplicate]

Question

I can easily create a class like

class MyEnum(enum.Enum):
  BOB = "bob"
  RALPH = "ralph"
  ETC = "etc"

Then I can assign variables by enum value:

a = MyEnum('bob')

However -- I want to assign variables by things that could be the correct value. I.e., I'd like to do

a = MyEnum('bob')
b = MyEnum('Bob')
c = MyEnum('BOB')

and have them all work, and all map to the same enum value.

Is there a way of doing this without making a factory method? I've currently defined a create method, so a = MyEnum.create('Bob') works, but I'd like things to be seamless.

Answer 1

The thing you are looking for is called _missing_ and is available in the stdlib as of Python3.6, and in aenum¹ as of 2.0.

class MyEnum(Enum):

    BOB = "bob"
    RALPH = "ralph"
    ETC = "etc"

    @classmethod
    def _missing_(cls, value):
        for member in cls:
            if member.value == value.lower():
                return member

If _missing_ fails to return a MyEnum member then EnumMeta will raise an exception (so _missing_ doesn't have to worry about that part)².

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¹ Disclosure: I am the author of the Python stdlib Enum, the enum34 backport, and the Advanced Enumeration (aenum) library.

² Thanks, Aran-Fey, for bringing that up.