A more pythonic way to define an enum with dynamic members

Question

I needed to create an enum to represent the ISO country codes. The country code data comes from a json file which can be obtained from: https://github.com/lukes/ISO-3166-Cou

Answer 1

Update

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
    _file = 'some_file.json'
    _name = 'alpha-2'
    _value = {
            1: ('alpha-2', None),
            2: ('country-code', lambda c: int(c)),
            3: ('name', None),
            }

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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

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

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

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

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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']] = (
                country['alpha-2'],
                int(country['country-code']),
                country['name'],
                )

    # return a dict of choices by abbr or country code to name
    @classmethod
    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

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

>>> Country('AF')


>>> Country(4)


>>> Country('Afghanistan')

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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+.