Automatically add constants for each of the choices in a Django model

I'm constantly doing the following pattern in Django:

class MyModel(models.Model):

    FOO = 1
    BAR = 2
    GOO = 3

    BLAH_TYPES = (
        (FOO, 'Foodally boogaly'),
        (BAR, 'Bar bar bar bar'),
        (GOO, 'Goo goo gaa gaa')开发者_Go百科,
    )

    TYPE_FOR_ID = dict(BLAH_TYPES)

    ID_FOR_TYPE = dict(zip(TYPE_FOR_ID.values(), TYPE_FOR_ID.keys()))

    blah = models.IntegerField(choices=BLAH_TYPES)

Is there a good pattern that other people follow that achieves the same effect (i.e. I have access to constants with names and dictionaries that go both ways) without so much code?

Carl Meyer's django-model-utils library has an excellent solution for this - the Choices class, which allows you to declare a list of choices with access via human-readable attributes.

This is about the most compact way to initialize your constants:

# foobar choices constants
FOO, BAR, BAZ = range(3) 

# bebop choices constants (if you prefer this to readability)
(BUU,
BAA,
DII,
DUU) = range(4)

# then, in a galaxy far away, much to your expectations:
>> FOO
0
>> DII
2

In any case, I usually whip up a const.py and keep all the insanity in there (just looking at one that's 98 lines long), but definitely move them out of the model class and make them a part of the module data to conserve time and memory, unless your doing something dynamic.

Otherwise, your doing it about as good as it can possibly get. I also do a BLAH_TYPES, to conform to the Django choices structure every developer is accustomed to reading. That's to part you can't avoid and can't make any shortcuts. And, if I need those transformations, such as ID_FOR_TYPE, I just define them right beneath the choices. Readable, clean and compact.

I had the same itch, and that's what I wrote:

from django.db import models
from django.db.models.base import ModelBase
import re

class ModelBaseWithChoices(ModelBase):
    def __new__(cls, name, bases, attrs):
        def format_label(label):
            return re.sub('[^A-Z]+', '_', label.upper()).strip('_')

        def get_choices(attrs):
            for attr, value in attrs.items():
                if attr.endswith('_CHOICES') and isinstance(value, tuple):
                    base = '_'.join(attr.split('_')[:-1])
                    for val, label in value:
                        yield '_'.join((base, format_label(label))), val

        attrs.update(list(get_choices(attrs)))
        return super(ModelBaseWithChoices, cls).__new__(cls, name, bases, attrs)

class ModelWithChoices(models.Model):
    __metaclass__ = ModelBaseWithChoices

    class Meta:
        abstract = True

From there, you can rewrite MyModel as:

class MyModel(ModelWithChoices):
    BLAH_CHOICES = ((1, 'Foodally boogaly'),
                    (2, 'Bar bar bar bar'),
                    (3, 'Goo goo gaa gaa'))

    blah = models.IntegerField(choices = BLAH_CHOICES)

And have all the constants automatically created for you in the model. From the Django shell:

>>> MyModel.BLAH_FOODALLY_BOOGALY
1
>>> MyModel.BLAH_GOO_GOO_GAA_GAA
3