'ENUM' IN PYTHON

Monaj Singh

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Posted by  Monaj Singh
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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?

  1. Mayank Tripathi

    Post:397

    Points:3117
    Re: '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.


    o use backports, do $ pip install enum34, installing enum (no numbers) will install a completely different and incompatible version.

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

    class Animals(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'

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