具有可变数量属性的枚举成员的 Python 元类

Question

I am new to Python's metaclasses and I am currently trying to achieve the following:

from enum import Enum, EnumMeta

class FlexEnumMeta(EnumMeta):
   # see the attempt for the implementation below
   ...

class FlexEnum(Enum, metaclass=FlexEnumMeta, attrs=('foo', 'bar')):
   X = 'abc', 123
   Y = 'def', 456

and I would expect it to work as follow:

FlexEnum.X.foo
>>> 'abc'

I read parts of the source code of Enum and aenum to try to understand, and as far as I got was with this code for FlexEnumMeta:

class FlexEnumMeta(EnumMeta):

    @classmethod
    def __prepare__(metacls, cls, bases, attrs=None, **kwargs):
        return {}

    def __new__(metacls, name, bases, clsdict, attrs=None, **kwargs):
        # Proper way to get an _EnumDict,
        # to be passed to super().__new__
        enum_dict = super().__prepare__(name, bases, **kwargs)

        # Enumeration class members
        members = []

        for member_name, values in clsdict.items():
            # Copy original clsdict in final class members list
            if member_name.startswith('_'):
                enum_dict[member_name] = values
                continue

            # Create correspondance between attributes names and values
            value_dict = dict(zip(attrs, values))
            members.append((member_name, value_dict))

        # Copy custom class members in final class members list
        for key, value in members:
            enum_dict[key] = value

        return super().__new__(metacls, name, bases, enum_dict)

class FlexEnum(Enum, metaclass=FlexEnumMeta, attrs=('foo', 'bar')):
    X = 'abc', 123

FlexEnum.X
>>> <FlexEnum.X: {'foo': 'abc', 'bar': 123}>
FlexEnum.X.value['foo']
>>> 'abc'

I tried using aenum's MultiValue setting, but I need to have a dict as one of my attributes, and those aren't hashable. And in the end, this is kind of an exercise for me.

Answer 1

All you need is to define FlexEnum.__init__ :

import enum


class FlexEnum(enum.Enum):
    def __init__(self, foo, bar):
        self.foo = foo
        self.bar = bar

    X = 'abc', 123
    Y = 'def', 456

Then

>>> FlexEnum.X.foo
'abc'

The value of the member itself will be the tuple. If you'd like something else, you can override __new__ . There is some more information in the documentation, When to use __new__() vs. __init__() .