Python Enum class membership

Enum does have a __contains__ method, but it checks for member names rather than member values:

def __contains__(cls, member):
    return isinstance(member, cls) and member._name_ in cls._member_map_

Internally(in CPython) they do have a private attribute that maps values to names(will only work for hashable values though):

>>> 2 in TestEnum._value2member_map_
True
>>> 3 in TestEnum._value2member_map_
False

But it's not a good idea to rely on private attributes as they can be changed anytime, hence you can add your own method that loops over __members__.values():

>>> class TestEnum(Enum):
...     a = 0
...     b = 1
...     c = 2
...
...     @classmethod
...     def check_value_exists(cls, value):
...         return value in (val.value for val in cls.__members__.values())
...

>>>
>>> TestEnum.check_value_exists(2)
True
>>> TestEnum.check_value_exists(3)
False