How Can I Effectively Use and Represent Enums in Python?

Python Enum Representation

Python provides a native Enum type in version 3.4 and above. For earlier versions, you can use third-party libraries like enum34 or aenum.

Using enum34 or stdlib Enum:

from enum import Enum
Animal = Enum('Animal', 'ant bee cat dog')

Animal.ant  # <Animal.ant: 1>
Animal['ant']  # <Animal.ant: 1> (string lookup)
Animal.ant.name  # 'ant' (inverse lookup)

Using aenum:

from aenum import Enum
Animal = Enum('Animal', 'ant bee cat dog')

Animal.ant  # same as enum34
Animal['ant']  # same as enum34
Animal.ant.name  # same as enum34

Using Earlier Python Versions:

For earlier Python versions, you can use a custom function like this:

def enum(**enums):
    return type('Enum', (), enums)

Numbers = enum(ONE=1, TWO=2, THREE='three')
Numbers.ONE  # 1
Numbers.TWO  # 2
Numbers.THREE  # 'three'

Automatic Enumeration:

You can also use the following function for automatic enumeration:

def enum(*sequential, **named):
    enums = dict(zip(sequential, range(len(sequential))), **named)
    return type('Enum', (), enums)

Numbers = enum('ZERO', 'ONE', 'TWO')
Numbers.ZERO  # 0
Numbers.ONE  # 1

Reverse Mapping:

To support converting enum values back to names:

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)

Numbers = enum('ZERO', 'ONE', 'TWO')
Numbers.reverse_mapping['1']  # 'ONE'

Typing.Literal (MyPy):

In MyPy, you can define enums using Literal:

from typing import Literal

Animal = Literal['ant', 'bee', 'cat', 'dog']

def hello_animal(animal: Animal):
    print(f"hello {animal}")

This will prevent assignments of non-enum values.

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