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Assigning a default value to an enum class when the value provided to the constructor is not enumerated

June 6, 2023

I have an enum class:

import enum

class Version(enum.IntEnum):
    VERSION_1 = 1
    VERSION_2 = 2
    VERSION_UNKNOWN = 99

When a user initializes the enum class with a value that is not listed as a class field, I would like him to get VERSION_UNKNOWN i.e. the following snippet to execute successfully:

e = enum(3)
assert e == Version.VERSION_UNKNOWN

Is there any way to do that sort of thing?

>Solution :

i think the enum build-in _missing_ is your friend: https://docs.python.org/3/library/enum.html#enum.Enum._missing_

import enum

class Version(enum.IntEnum):
    VERSION_1 = 1
    VERSION_2 = 2
    VERSION_UNKNOWN = 99

    @classmethod
    def _missing_(cls, value):
        return Version.VERSION_UNKNOWN