为什么Python枚举中的可变值是同一个对象？

问题描述

在尝试枚举成员的不同值类型时，当值可变时，我发现了一些奇怪的行为。

如果我将枚举的值定义为不同的列表，则成员的行为与枚举值相似是像 str 或 int 的典型不变类型，即使我可以更改成员的值，使得两个枚举成员的值是相同的：

 >> ;> class color（enum.Enum）：
 black = [1,2] 
 blue = [1,2,3] 
 
>>> Color.blue是Color.black 
 False 
>>> Color.black == Color.blue 
 False 
>>> Color.black.value.append（3）
>>> Color.black 
< Color.black：[1，2，3]> 
>>> Color.blue 
< Color.blue：[1，2，3]> 
>>> Color.blue == Color.black 
 False 
>>> Color.black.value == Color.blue.value 
 True 
  

但是，如果我将值定义为相同的列表，每个成员的值似乎是相同的对象，因此一个成员的值的任何变化都会影响所有成员：

 >>> class color（enum.Enum）：
 black = [1,2,3] 
 blue = [1,2,3] 
 
>>> Color.blue是Color.black 
 True 
>>> Color.black == Color.blue 
 True 
>>> Color.black.value.append（4）
>>> Color.black 
< Color.black：[1，2，3，4]> 
>>> Color.blue 
< Color.black：[1，2，3，4]> 
>>> Color.blue == Color.black 
 True 
  

为什么枚举这样做？是否是预期的行为或是一个错误？

注意： 我不打算实际使用枚举这种方式，我只是尝试使用枚举成员使用非标准值

解决方案

从：

$ b $给定两个成员A和B具有相同的值（和A定义为第一个），B是A的别名。A和B的值的副值查找将返回A. B的姓名查找也将返回A：

 >>>类形状（枚举）：
 ... square = 2 
 ... diamond = 1 
 ... circle = 3 
 ... alias_for_square = 2 
 ... 
>>> Shape.square 
< Shape.square：2> 
>>> Shape.alias_for_square 
< Shape.square：2> 
>>>形状（2）
< Shape.square：2> 
  

这个操作是相等的，即使值是可变的。由于您为黑色和蓝色定义了相等的值，而黑色首先， blue 是黑色的别名。

While experimenting with different value types for Enum members, I discovered some odd behavior when the values are mutable.

If I define the values of an Enum as different lists, the members still behave similarly to when the Enum values are typical immutable types like str or int, even though I can change the values of the members in place so that the values of the two Enum members are the same:

>>> class Color(enum.Enum):
        black = [1,2]
        blue = [1,2,3]

>>> Color.blue is Color.black
False
>>> Color.black == Color.blue
False
>>> Color.black.value.append(3)
>>> Color.black
<Color.black: [1, 2, 3]>
>>> Color.blue
<Color.blue: [1, 2, 3]>
>>> Color.blue == Color.black
False
>>> Color.black.value == Color.blue.value
True

However, if I define the values to be identical lists, each member's value seems to be the same object, and thus any mutation of one member's value affects all members:

>>> class Color(enum.Enum):
        black = [1,2,3]
        blue = [1,2,3]

>>> Color.blue is Color.black
True
>>> Color.black == Color.blue
True
>>> Color.black.value.append(4)
>>> Color.black
<Color.black: [1, 2, 3, 4]>
>>> Color.blue
<Color.black: [1, 2, 3, 4]>
>>> Color.blue == Color.black
True

Why does Enum behave this way? Is it the intended behavior or is it a bug?

NOTE: I'm not planning on actually using Enums this way, I was simply experimenting with using non-standard values for Enum members

解决方案

From the docs:

This operates by equality, even when the values are mutable. Since you defined equal values for black and blue, with black first, blue is an alias for black.

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