I'm mainly a C# developer, but I'm currently working on a project in Python.
How can I represent the equivalent of an Enum in Python?
Enums have been added to Python 3.4 as described in PEP 435. It has also been backported to 3.3, 3.2, 3.1, 2.7, 2.6, 2.5, and 2.4 on pypi.
$ pip install enum34
$ pip install aenum
enum (no numbers) will install a completely different and incompatible version.
from enum import Enum # for enum34, or the stdlib version # from aenum import Enum # for the aenum version Animal = Enum('Animal', 'ant bee cat dog') Animal.ant # returns <Animal.ant: 1> Animal['ant'] # returns <Animal.ant: 1> (string lookup) Animal.ant.name # returns 'ant' (inverse lookup)
class Animal(Enum): ant = 1 bee = 2 cat = 3 dog = 4
In earlier versions, one way of accomplishing enums is:
def enum(**enums): return type('Enum', (), enums)
which is used like so:
>>> Numbers = enum(ONE=1, TWO=2, THREE='three') >>> Numbers.ONE 1 >>> Numbers.TWO 2 >>> Numbers.THREE 'three'
You can also easily support automatic enumeration with something like this:
def enum(*sequential, **named): enums = dict(zip(sequential, range(len(sequential))), **named) return type('Enum', (), enums)
and used like so:
>>> Numbers = enum('ZERO', 'ONE', 'TWO') >>> Numbers.ZERO 0 >>> Numbers.ONE 1
Support for converting the values back to names can be added this way:
def enum(*sequential, **named): enums = dict(zip(sequential, range(len(sequential))), **named) reverse = dict((value, key) for key, value in enums.iteritems()) enums['reverse_mapping'] = reverse return type('Enum', (), enums)
This overwrites anything with that name, but it is useful for rendering your enums in output. It will throw KeyError if the reverse mapping doesn't exist. With the first example:
>>> Numbers.reverse_mapping['three'] 'THREE'
Before PEP 435, Python didn't have an equivalent but you could implement your own.
Myself, I like keeping it simple (I've seen some horribly complex examples on the net), something like this ...
class Animal: DOG = 1 CAT = 2 x = Animal.DOG
In Python 3.4 (PEP 435), you can make Enum the base class. This gets you a little bit of extra functionality, described in the PEP. For example, enum members are distinct from integers, and they are composed of a
name and a
class Animal(Enum): DOG = 1 CAT = 2 print(Animal.DOG) # <Animal.DOG: 1> print(Animal.DOG.value) # 1 print(Animal.DOG.name) # "DOG"
If you don't want to type the values, use the following shortcut:
class Animal(Enum): DOG, CAT = range(2)
Enum implementations can be converted to lists and are iterable. The order of its members is the declaration order and has nothing to do with their values. For example:
class Animal(Enum): DOG = 1 CAT = 2 COW = 0 list(Animal) # [<Animal.DOG: 1>, <Animal.CAT: 2>, <Animal.COW: 0>] [animal.value for animal in Animal] # [1, 2, 0] Animal.CAT in Animal # True