Python中基于字符串的枚举 [英] String-based enum in Python

问题描述

要封装状态列表，请使用 enum 模块:

To encapsulate a list of states I am using enum module:

from enum import Enum

class MyEnum(Enum):
    state1='state1'
    state2 = 'state2'

state = MyEnum.state1
MyEnum['state1'] == state  # here it works
'state1' == state  # here it does not throw but returns False (fail!)

但是，问题是我需要在脚本的许多上下文中将这些值无缝地用作字符串，例如:

However, the issue is that I need to seamlessly use the values as strings in many contexts in my script, like:

select_query1 = select(...).where(Process.status == str(MyEnum.state1))  # works but ugly

select_query2 = select(...).where(Process.status == MyEnum.state1)  # throws exeption

如何避免调用其他类型转换(上面的 str(state))或基础值( state.value )?

How to do it avoiding calling additional type conversion (str(state) above) or the underlying value (state.value)?

推荐答案

似乎与 Enum 同时从 str 类继承就足够了:

It seems that it is enough to inherit from str class at the same time as Enum:

class MyEnum(str, Enum):
    state1='state1'
    state2 = 'state2'

棘手的部分是，继承链中类的顺序很重要，如下所示:

The tricky part is that the order of classes in the inheritance chain is important as this:

class MyEnum(Enum, str):
    state1='state1'
    state2 = 'state2'

抛出:

TypeError: new enumerations should be created as `EnumName([mixin_type, ...] [data_type,] enum_type)`

使用正确的类，可以对 MyEnum 进行以下操作:

With the correct class the following operations on MyEnum are fine:

print('This is the state value: ' + state)

---

作为旁注，看来格式化的格式不需要特殊的继承技巧字符串甚至仅对 Enum 继承有效:

msg = f'This is the state value: {state}'  # works without inheriting from str

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