枚举 class，类型为 `type` 作为 mixin

Question

docs 声明可以创建一个枚举 class，其成员恰好是某种类型，方法是将该类型作为混合类型添加到枚举 class 中：

While :class:IntEnum is part of the :mod:enum module, it would be very simple to implement independently::
class IntEnum(int, Enum):
    pass
This demonstrates how similar derived enumerations can be defined; for example a :class:StrEnum that mixes in :class:str instead of :class:int.

Some rules:

When subclassing :class:Enum, mix-in types must appear before :class:Enum itself in the sequence of bases, as in the :class:IntEnum example above.

While :class:Enum can have members of any type, once you mix in an additional type, all the members must have values of that type, e.g. :class:int above. This restriction does not apply to mix-ins which only add methods and don't specify another type.

When another data type is mixed in, the :attr:value attribute is not the same as the enum member itself, although it is equivalent and will compare equal.

%-style formatting: %s and %r call the :class:Enum class's :meth:__str__ and :meth:__repr__ respectively; other codes (such as %i or %h for IntEnum) treat the enum member as its mixed-in type.

:ref:Formatted string literals <f-strings>, :meth:str.format, and :func:format will use the mixed-in type's :meth:__format__
unless :meth:__str__ or :meth:__format__ is overridden in the subclass, in which case the overridden methods or :class:Enum methods will be used. Use the !s and !r format codes to force usage of the :class:Enum class's :meth:__str__ and :meth:__repr__ methods.

我试图创建一个枚举，其成员是类型（type 类型的对象），但由于 type 是一个特殊的 class（它是一个元 class 多于 class)，我收到了一堆错误，例如 mro、__new__、__init__ 等的参数不匹配：

import enum

class A: pass

class B: pass

class C(B): pass


class MyTypes(type, enum.Enum):
    SPAM = A
    EGGS = C

错误示例：

Traceback (most recent call last):
  File "<file>", line 10, in <module>
    class MyTypes(type, enum.Enum):
  File "<file>", line 182, in __new__
    dynamic_attributes = {k for c in enum_class.mro()
TypeError: descriptor 'mro' of 'type' object needs an argument

有办法实现吗？

我意识到这可能是一个 XY 问题，所以我将解释我的具体示例。在我正在开发的纸牌游戏中，我有一个 Card class 层次结构；每个 subclasses 代表不同的卡片类型。但是，游戏中的卡牌类型与Card的子class卡牌类型之间的映射可能不是一对一的；例如，可能有一些中间抽象 classes 作为实现帮助，但不代表实际的卡类型。

所以我想做一个包含所有游戏卡类型的枚举，我希望成员是实现这些类型的实际具体子classes，这样我就可以轻松地互操作枚举成员和实际的 classes：这个想法是访问 class 属性，实例化它们，等等，而不必每次都使用 .value （因为在某些情况下，我可能不得不使用一些东西是枚举的成员或 class 本身）。

Answer 1

简短回答：不，目前无法将 type 混入枚举。

混合数据类型的目的有两个：

确保所有成员都是该类型

class Number(int, Enum):
    ONE = 1
    TWO = 2
    THREE = 'three'
# ValueError: invalid literal for int() with base 10: 'three'

使成员可以直接用作该类型

class Number(int, Enum):
    ONE = 1
    TWO = 2
Number.ONE + 2
# 3

如您所述，type 不是一种数据类型——它是一种元类。它需要特殊支持才能工作。您的用例是什么？

披露：我是 Python stdlib Enum, the enum34 backport, and the Advanced Enumeration (aenum) 库的作者。

枚举 class，类型为 `type` 作为 mixin

Enum class with type `type` as mixin

python

enums

python-class