[FIXED] String-based enum in Python

Issue

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!)

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

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

Solution

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'

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'

throws:

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

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

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

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As a side note, it seems that the special inheritance trick is not needed for formatted strings which work even for Enum inheritance only:

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

Answered By - sophros