String-based enum in Python

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.

If associated string values are valid Python names then you can get names of enum members using .name property like this:

from enum import Enum
class MyEnum(Enum):
    state1=0
    state2=1

print (MyEnum.state1.name)  # 'state1'

a = MyEnum.state1
print(a.name)  # 'state1'

If associated string values are arbitrary strings then you can do this:

class ModelNames(str, Enum):
    gpt2 = 'gpt2'
    distilgpt2 = 'distilgpt2'
    gpt2_xl = 'gpt2-XL'
    gpt2_large = 'gpt2-large'

print(ModelNames.gpt2) # 'ModelNames.gpt2'
print(ModelNames.gpt2 is str) # False
print(ModelNames.gpt2_xl.name) # 'gpt2_xl'
print(ModelNames.gpt2_xl.value) # 'gpt2-XL'

Try this online: https://repl.it/@sytelus/enumstrtest

Simply use .value :

MyEnum.state1.value == 'state1'
# True

If you want to work with strings directly, you could consider using

MyEnum = collections.namedtuple(
    "MyEnum", ["state1", "state2"]
)(
    state1="state1", 
    state2="state2"
)

rather than enum at all. Iterating over this or doing MyEnum.state1 will give the string values directly. Creating the namedtuple within the same statement means there can only be one.

Obviously there are trade offs for not using Enum, so it depends on what you value more.

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

what is wrong with using the value?

Imho, unless using Python version 3.11 with StrEnum I just override the __str__(self) method in the proper Enum class:

class MyStrEnum(str, Enum):

    OK     = 'OK'
    FAILED = 'FAILED'

    def __str__(self) -> str:
        return self.value

Best

With auto:

from enum import Enum, auto

class AutoStrEnum(str, Enum):
    """
    StrEnum where auto() returns the field name.
    See https://docs.python.org/3.9/library/enum.html#using-automatic-values
    """
    @staticmethod
    def _generate_next_value_(name: str, start: int, count: int, last_values: list) -> str:
        return name

class MyEnum(AutoStrEnum):
    STATE_1 = auto()
    STATE_2 = auto()

Try it:

MyEnum.STATE_1 == "STATE_1"  # True