python - Python 中基于字符串的枚举

Question

为了封装状态列表，我正在使用 enum 模块:

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:

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

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

如何避免调用额外的类型转换(上面的str(state))或基础值(state.value)？

Answer 1

看来和Enum同时继承str类就够了:

from enum import 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:

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

抛出:

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

使用正确的类可以在 MyEnum 上进行以下操作:

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

---

附带说明一下，formatted strings 似乎不需要特殊的继承技巧。甚至只对 Enum 继承有效:

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