Enums in

About Enums

In Python, an enum is a set of unique names that are bound unique, constant values. Enums are defined by inheriting an Enum class. Built-in enum types are available in the module enum and the class Enum can be imported using from enum import Enum.

from enum import Enum

class Color(Enum):
    RED = 1
    GREEN = 2

Note that the values of the enum members can be any data types such as str, tuple, float, etc.

class Color(Enum):
    RED = 'red'
    GREEN = 'green'

Enums can also be created using function-call syntax.

from enum import Enum

Animal = Enum('Animal', 'ANT BEE CAT DOG')
list(Animal)
#=> [<Animal.ANT: 1>, <Animal.BEE: 2>, <Animal.CAT: 3>, <Animal.DOG: 4>]

Animal.ANT.value
#=> 1

When assigning the same value to two members in an enum, the latter assigned member will be an alias to the former one. It is not allowed to use the same name for two different members of an enum.

class Color(Enum):
    RED = 1
    GREEN = 2
    ALIAS_OF_RED = 1

Color.ALIAS_OF_RED
#=> <Color.RED: 1>

Iterating through the members of the enum can be done with the standard for member in syntax:

for member in Color:
    print((member.name, member.value))
#=> (RED, 1)
#=> (GREEN, 2)

# __members__.items() helps you to loop through alias as well
for member in Color.__members__.items():
    print(member)
#=> ('RED', <Color.RED: 1>)
#=> ('GREEN', <Color.GREEN: 2>)
#=> ('ALIAS_OF_RED', <Color.RED: 1>)

Enum members can be compared using is (identity operator) or is not. The == or != (equality operators) work likewise:

a = Color.RED

a is Color.RED
#=> True

a == Color.RED
#=> True

To assign integer values, the auto() function starts with 1 and automatically sets subsequent values.

class Shape(Enum):
    CIRCLE = auto()
    SQUARE = auto()
    OVAL = auto()

To disallow aliasing (preventing duplicate values with different names), the class decorator @enum.unique decorator may be used.

@enum.unique
class Shape(Enum):
    CIRCLE = 1
    SQUARE = 2
    TRIANGLE = 1
#=> ValueError: duplicate values found in <enum 'Shape'>: TRIANGLE -> CIRCLE

To access an enum member for a given value, this notation can be used: <EnumName>(<value>).

g = Color(2)

g is Color.GREEN
#=> True

g
#=> <Color.GREEN: 2>

A custom restricted Enum can be written by subclassing the Enum class with any mix-in or data-type. For example:

class StrEnum(str, Enum):
    pass

Subclassing Enum is only allowed if the enum does not define any members. See the enum how-to and the enum cookbook for more details and explanations.