How to construct a case insensitive enum?

Question

I have a simple Python 2.7 enum:

from enum import Enum

class Label(enum):
    RedApple = 1
    GreenApple = 2

I would like to be able create enum objects using case-insensitive keys:

fruitname = "redapple"
a = Label[fruitname]

I've tried to create an __init__ method:

def __init__(self, key):
    super(Label, self).__init__()
    pass # do comparison here

but I keep running into errors:

super(Label, self).__init__()
NameError: global name 'Label' is not defined

I'd like to do a comparison on key.lower().strip(). Is this even possible?

Answer 1

enum have missing function which can be overridden to make enum case insensitive. As per documentation https://docs.python.org/3.11/howto/enum.html missing – a lookup function used when a value is not found; may be overridden

example

class Status(enum.Enum):
   @classmethod
   def _missing_(cls, value):
      for member in cls:
         if member.value == value.upper():
            return member
   SUCCESS = 'SUCCESS'
   FAILURE = 'FAILURE'

print(Status('success'))

Output

Status.SUCCESS

Answer 2

Not 100% sure this will work in Python 2.7, but I came up with a simple way to make it work exactly as requested for Python 3.6+.

The idea is that lookup for names is done by the class using square brackets, which means that it uses __getitem__ from the metaclass. So you can make a simple metaclass that implements a case insensitive search. Since it will extend the existing EnumMeta, it will be totally compatible with existing enums:

class CaseInsensitiveEnumMeta(EnumMeta):
    def __getitem__(self, item):
        if isinstance(item, str):
            item = item.upper()
        return super().__getitem__(item)

This presupposes that your enums are all uppercase. Using it is pretty straightforward:

class Label(Enum, metaclass=CaseInsensitiveEnumMeta):
    REDAPPLE = 1
    GREENAPPLE = 2

I'm not sure you even need Enum in this case. The catch here is that your enums have to be all uppercase for this to work. If you want to have a truly insensitive search, you would have to make sure that all of the keys in __members__ are properly casefolded.

In the meantime, you can do

>>> Label['GreenApple']
Label.GREENAPPLE