Is it possible to define enums without values with Python?

Question

One advantage of enums in Java and other languages is that I do not have to care about specific values (in contrast to constants/static final members). For example, in Java I can do the following:

public enum Color {
    RED, BLUE;
}

At least to my knowledge, in python I have to do the following:

class Color(Enum) {
    RED = "red" # or e.g 1
    BLUE = "blue" # or e.g. 2
}

If I have an enum with hundreds of names, then this can get quite cumbersome, because I always have to keep track whether a value was already assigned to a name or not. Is it maybe possible to achieve the same result as in Java without resorting to generators or the like?

See docs.python.org/3/library/enum.html#using-automatic-values — Thierry Lathuille
– Thierry Lathuille, Commented Oct 20, 2019 at 9:29

Greg Hewgill · Accepted Answer · 2019-10-20 09:28:59Z

40

If you're using Python 3.6 or later, you can use enum.auto():

from enum import Enum, auto

class Color(Enum):
    RED = auto()
    BLUE = auto()

The documentation for the enum library describes this and other useful features like the @unique decorator.

answered Oct 20, 2019 at 9:28

Greg Hewgill

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1 Comment

matanox Over a year ago

Wow, it can auto-count. Did they use AI for it?

Daniel Roseman · Accepted Answer · 2019-10-20 09:30:52Z

31

One way is to use the Enum base class as a callable:

Color = Enum('Color', 'RED BLUE GREEN ORANGE')

answered Oct 20, 2019 at 9:30

Daniel Roseman

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4 Comments

agent nate Over a year ago

Is there a downside to this method?

habrewning Over a year ago

Why would you expect downsides? This method is officially explained in the documentation that you linked, so it should be as good as the class syntax.

Greg7000 Over a year ago

With this method you are not stuck with '=' which is closer to what is asked by the questions. I am also glad to see that Intellisence (pylance) manage to make a link between the Enum and the values

Greg7000 Over a year ago

Well there is a small downside, Intellisence (pylance) does work but you need to dig your param in the available options. With the @Greg Hewgill option, you don't have this issue but you are stuck again with '= ...'

habrewning · Accepted Answer · 2023-04-22 10:41:41Z

The answer from Daniel Roseman is an elegant solution, that is in line with the official documentation and that should be appropriate in most cases.

Only for completeness here are a few other options.

class Color(Enum):
    RED, BLUE = range(2)

This will even work without the enum package.

class Color:
    RED, BLUE = range(2)

But this solution has some drawbacks. For example if you print Color.RED, you don't see the name, but the number.

In principle an enum is just a list of constants. So even the following works if you completely define it without a surrounding class.

RED, BLUE = range(2)

I don't want to discuss the advantages and disadvantages of this. There may be specific uses cases of such code.

Note: It must be said here, that range(2) starts counting at 0. So the first value, when used as a boolean expression is evaluated to False. This is normally not, what someone wants. It could be a nice feature in very specific situations (if your first value is intentionally something like INVALID or UNDEFINED). But normally it should be better to use range(1,3) instead of range(2).

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