How Do I Implement and Use Enumerations in Python?

Implementing Enumerations in Python

Python provides a built-in enum module in Python 3.4 or above. This module allows for the representation of enumerations, which are collections of named constants. To use it, you can follow these steps:

1. Import the enum module:

   import enum

2. Define the enumeration:

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

3. Access the members of the enumeration:

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

Alternatively, you can define an enumeration using a class-based approach:

class Animal(enum.Enum):
    ant = 1
    bee = 2
    cat = 3
    dog = 4

Earlier Versions of Python

In earlier versions of Python, you can create your own custom enum functionality using a class:

class Enum(object):
    def __init__(self, *args):
        self.keys = args

    def __getattr__(self, attr):
        try:
            return attr, self.keys.index(attr)
        except:
            raise AttributeError(attr)

Using typing.Literal in MyPy

When using MyPy for type checking, you can also express enumerations using typing.Literal:

from typing import Literal

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

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