A More Pythonic Way To Define An Enum With Dynamic Members

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-Countries-

Solution 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),
            }

---

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'))],
        )

---

The aenum way

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

---

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')>

---

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

This requires aenum 2.0.5+.

Solution 2:

How about this?

data = json.load(open('slim-2.json'))
CountryCode = enum.Enum('CountryCode', [
    (x['alpha-2'], int(x['country-code'])) for x in data
])
CountryCode._names = {x['alpha-2']: x['name'] for x in data}
CountryCode.__str__ = lambda self: self._names[self.name]
CountryCode.choices = lambda: ((e.value, e.name) for e in CountryCode)

• Replaced [...data[i]... for i in range(len(data))] with [...x... for x in data]; You can itearte sequence (list, data in the code) without using indexes.
• Used CountryCode.attr = ... consistently; instead of mixing CountryCode.attr = ... and setattr(CountryCode, 'attr', ...).

Solution 3:

Yes, there is a way to define the enum using the alternate declaration syntax you want. It works by hiding the "ugly" code in a metaclass derived from enum.EnumMeta. If you wished, it would also be possible to define the choices() class method there, too.

import enum
import json

class CountryCodeMeta(enum.EnumMeta):
    def __new__(metacls, cls, bases, classdict):
        data = classdict['data']
        names = [(country['alpha-2'], int(country['country-code'])) for country in data]

        temp = type(classdict)()
        for name, value in names:
            temp[name] = value

        excluded = set(temp) | set(('data',))
        temp.update(item for item in classdict.items() if item[0] not in excluded)

        return super(CountryCodeMeta, metacls).__new__(metacls, cls, bases, temp)

class CountryCode(enum.Enum, metaclass=CountryCodeMeta):
    data = json.load(open('slim-2.json'))

    @classmethod
    def choices(cls):
        return ((member.value, name) for name, member in cls.__members__.items())