[Python] How to define an alias value for an enum member?

In Python, an enum member carries an underlying value, which can be obtained by reading the value attribute. Conversely, an enum member can be obtained from its value by calling the enum type.

class Food(enum.Enum):
MEAT = 'meat'
DAIRY = 'dairy'

print(Food.MEAT.value) # 'meat'
print(Food('meat') is Food.MEAT) # True


I would like it to be possible to obtain the same enum member by passing several different values; obviously, only one of them would be canonical and obtainable from the value attribute. I can do it this way:

class Food(enum.Enum):
MEAT = 'meat'
DAIRY = 'dairy'

@classmethod
def from_str(cls, item):
match item:
case 'spam'|'ham':
return cls.MEAT
case 'eggs'|'milk':
return cls.DAIRY
return cls(item)


and then remember to keep using Food.from_str(s) instead of Food(s). This is workable, although I would rather have the aliases in the definition of the member instead of repeating members in a helper method (like in my other question involving Python enums). But there are also other problems with it:

#!/usr/bin/env python3
import argparse
import enum

class Food(enum.Enum):
MEAT = 'meat'
DAIRY = 'dairy'

@classmethod
def from_str(cls, item):
match item:
case 'spam'|'ham':
return cls.MEAT
case 'eggs'|'milk':
return cls.DAIRY
return cls(item)

parser = argparse.ArgumentParser()
parser.add_argument('food', type=Food.from_str)
args = parser.parse_args()

print(args.food)


When I invoke this script with “bread” as the command-line argument, argparse complains about an “invalid from_str value”. So I would rather use type=Food as a add_argument argument, so that the type is identified correctly in the error message.

How can this be solved?

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