Django natural sorted ModelChoiceField

django-natsort.py

# Tested with Django 1.7.1
# and natsort 3.5.1
# Very hackish, but that's the easiest and fastest solution I've found.

import natsort
from django import forms

# Adapted from private forms.ModelChoiceIterator
class NatSortedModelChoiceIterator(object):
    def __init__(self, field):
        self.field = field
        self.queryset = field.queryset

    def _get_choices(self):
        if self.field.empty_label is not None:
            yield ("", self.field.empty_label)
        if self.field.cache_choices:
            if self.field.choice_cache is None:
                self.field.choice_cache = [
                    self.choice(obj) for obj in self.queryset.all()
                ]
            for choice in self.field.choice_cache:
                yield choice
        else:
            for obj in self.queryset.all():
                yield self.choice(obj)

    def __iter__(self):
        choices = list(self._get_choices())

        # choices is a list of choice tuples, index 1 is the label
        for choice in natsort.natsorted(choices, key=lambda model: model[1]):
            yield choice

    def __len__(self):
        return (len(self.queryset) +
            (1 if self.field.empty_label is not None else 0))

    def choice(self, obj):
        return (self.field.prepare_value(obj), self.field.label_from_instance(obj))


class NatSortedModelChoiceField(forms.ModelChoiceField):
    def _get_choices(self):
        if hasattr(self, '_choices'):
            return self._choices

        return NatSortedModelChoiceIterator(self)

    choices = property(_get_choices, forms.ChoiceField._set_choices)


class NatSortedModelMultipleChoiceField(forms.ModelMultipleChoiceField, NatSortedModelChoiceField):
    def __init__(self, *args, **kwargs):
        NatSortedModelChoiceField.__init__(self, *args, **kwargs)


# Example

class MyForm(forms.Form):
    field = NatSortedModelChoiceField(queryset=MyModel.objects.all())