在__str__上调用__init__会产生aenum.Enum [英] __init__ being called on __str__ result in aenum.Enum

问题描述

在尝试一些愚蠢的事情以使我的 __ str __ 方法在Enum成员上正常工作时，我发现了一些我不太理解的行为。我知道以下实现是错误的，但是我不知道它为什么会这样做。

While trying silly things to get my __str__ method working correctly on an Enum member, I discovered some behavior I don't really understand. I'm aware the following implementation is wrong, but I don't know why it does what it does.

请考虑以下类：

from aenum import Enum, AutoValue
class MyEnum(str, Enum, settings=AutoValue, init="value data1 data2"):

    __str__ = lambda self: self

    def __new__(cls, name, *args, **kwargs):
        member = str.__new__(cls)
        member._value_ = name
        return member

    @staticmethod
    def _generate_next_value_(name, *args, **kwargs):
        return (name,) + args

    member1 = 1, 2
    member2 = 3, 4

导入时，此功能按预期进行。 MyEnum.member1.data1 == 1 和 MyEnum.member1.data2 == 2 。但是，当我调用 str（MyEnum.member1）时，会抛出一个异常，说缺少'data2'的值。我在这里跟踪了代码，似乎正在调用 MyEnum.member1 .__ str __（）.__ init __（MyEnum.member1 .__ str __（））。我不太确定那是通话路径，而是结果。由于 MyEnum .__ init__是Enum .__ init __ 并且我们使用的是AutoValue，因此 init 方法需要两个参数。尝试设置 member1.data1 = member1 和 member1.data2 没有值。

On import, this works as exected. MyEnum.member1.data1 == 1 and MyEnum.member1.data2 == 2. However, when I call str(MyEnum.member1) an exception is thrown saying "missing value for 'data2'". I traced through the code here and it seems MyEnum.member1.__str__().__init__(MyEnum.member1.__str__()) is being called. I'm not positive that's the call path, but that's the result. And since MyEnum.__init__ is Enum.__init__ and we're using AutoValue, the init method is expecting two arguments. It's trying to set member1.data1 = member1 and member1.data2 doesn't have a value.

要清楚，我知道正确的解决方案是将 __ str __ 方法实现为 __ str__ = str .__ str __ 。但是，由于 isinstance（MyEnum.member1，str）== True 和 __ str __ 需要返回 str ...我不清楚为什么上面的实现会表现出来。

To be clear, I'm aware the correct solution is to implement the __str__ method as __str__ = str.__str__. However, since isinstance(MyEnum.member1, str) == True, and __str__ needs to return a str... I'm unclear why the above implementation would behave how it does.

1. 为什么要呼叫任何 __ init __ ？


2. 为什么返回 self 不够，因为 self 是 str ？


3. 有些不相关，为什么不设置值就不能实现呢？如果从init字符串中删除值，请在导入<$ c时删除 __ new __ 和 _generate_next_value _ 方法抛出$ c> TypeError 表示 str（）参数2必须为str，而不是int （... / aenum / init .py:1302）。

1. Why is any __init__ getting called?
2. Why is it insufficient to return self since self is an str?
3. Unrelated somewhat, by why could I not implement this without setting "value"? If you take away, value from the init string, remove the __new__ and _generate_next_value_ methods, on import a TypeError is thrown saying str() argument 2 must be str, not int (.../aenum/init.py:1302).

推荐答案

@ user2357112有权。

@user2357112 has the right of it.

详细说明您的观点：

1. 为什么不足返回 self ，因为 self 是 str ？
   

1. Why is it insufficient to return self since self is an str?

self 不是 str ，它是 MyEnum ，它是 str 子类-有它自己的 __ init __ ，然后调用它。 str 类没有 __ init __ 方法。

self is not a str, it's a MyEnum which is a str subclass -- a subclass that has it's own __init__, which then gets called. The str class does not have an __init__ method.

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