A more pythonic way to define an enum with dynamic members


Using JSONEnum at the bottom of When should I subclass EnumMeta instead of Enum?, you can do this:

class Country(JSONEnum):
    _init_ = 'abbr code country_name'  # remove if not using aenum
    _value = {
            1: ('alpha-2', None),
            2: ('country-code', lambda c: int(c)),
            3: ('name', None),

Original Answer

It looks like you are trying to keep track of three pieces of data:

  • country name
  • country code
  • country 2-letter abbreviaton

You should consider using a technique inspired by a namedtuple mixin as illustrated in this answer:

The stdlib way

We’ll need a base class to hold the behavior:

from enum import Enum
import json

class BaseCountry(Enum):

    def __new__(cls, record):
        member = object.__new__(cls)
        member.country_name = record['name']
        member.code = int(record['country-code'])
        member.abbr = record['alpha-2']
        member._value_ = member.abbr, member.code, member.country_name
        if not hasattr(cls, '_choices'):
            cls._choices = {}
        cls._choices[member.code] = member.country_name
        cls._choices[member.abbr] = member.country_name
        return member                

    def __str__(self):
        return self.country_name

    def choices(cls):
        return cls._choices.copy()

Then we can use that to create the actual Country class:

Country = BaseCountry(
        [(rec['alpha-2'], rec) for rec in json.load(open('slim-2.json'))],

The aenum way 1 2

from aenum import Enum, MultiValue
import json

class Country(Enum, init="abbr code country_name", settings=MultiValue):

    _ignore_ = 'this country'  # do not add these names as members

    # create members
    this = vars()
    for country in json.load(open('slim-2.json')):
        this[country['alpha-2']] = (

    # return a dict of choices by abbr or country code to name
    def choices(cls):
        mapping = {}
        for member in cls:
            mapping[member.code] = member.name
            mapping[member.abbr] = member.name
        return mapping

    # have str() print just the country name
    def __str__(self):
        return self.country_name

While I included the choices method, you may not need it:

>>> Country('AF')
<Country.AF: ('AF', 4, 'Afghanistan')>

>>> Country(4)
<Country.AF: ('AF', 4, 'Afghanistan')>

>>> Country('Afghanistan')
<Country.AF: ('AF', 4, 'Afghanistan')>

1 Disclosure: I am the author of the Python stdlib Enum, the enum34 backport, and the Advanced Enumeration (aenum) library.

2 This requires aenum 2.0.5+.

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