String-based enum in Python

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

from enum import 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)

---

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

By reading the documentation (i.e., I didn't try it because I use an older version of Python, but I trust the docs), since Python 3.11 you can do the following:

from enum import StrEnum

class Directions(StrEnum):
    NORTH = 'north',    # notice the trailing comma
    SOUTH = 'south'

print(Directions.NORTH)
>>> north

Please refer to the docs and the design discussion for further understanding.

If you're running python 3.6+, execute pip install StrEnum, and then you can do the following (confirmed by me):

from strenum import StrEnum

class URLs(StrEnum):
    GOOGLE = 'www.google.com'
    STACKOVERFLOW = 'www.stackoverflow.com'

print(URLs.STACKOVERFLOW)

>>> www.stackoverflow.com

You can read more about it here.

Also, this was mentioned in the docs - how to create your own enums based on other classes:

While IntEnum is part of the enum module, it would be very simple to implement independently:

class IntEnum(int, Enum): pass This demonstrates how similar derived enumerations can be defined; for example a StrEnum that mixes in str instead of int.

Some rules:

When subclassing Enum, mix-in types must appear before Enum itself in the sequence of bases, as in the IntEnum example above.

While Enum can have members of any type, once you mix in an additional type, all the members must have values of that type, e.g. int above. This restriction does not apply to mix-ins which only add methods and don’t specify another type.

When another data type is mixed in, the value attribute is not the same as the enum member itself, although it is equivalent and will compare equal.

%-style formatting: %s and %r call the Enum class’s str() and repr() respectively; other codes (such as %i or %h for IntEnum) treat the enum member as its mixed-in type.

Formatted string literals, str.format(), and format() will use the mixed-in type’s format() unless str() or format() is overridden in the subclass, in which case the overridden methods or Enum methods will be used. Use the !s and !r format codes to force usage of the Enum class’s str() and repr() methods.

Source: https://docs.python.org/3/library/enum.html#others

While a mixin class between str and Enum can solve this problem, you should always also think about getting the right tool for the job.

And sometimes, the right tool could easily just be a MODULE_CONSTANT with a string value. For example, logging has a few constants like DEBUG, INFO, etc with meaningful values - even if they're ints in this case.

Enums are a good tool and I often use them. However, they're intended to be primarily compared against other members of the same Enum, which is why comparing them to, for example, strings requires you to jump through an additional hoop.