Django UUIDField with primary key and default value that doesn't break `if self.id` checks inside `save()`

defaultuuidfield.py

import uuid
from django.db import models
from django.utils.encoding import force_text as force_unicode


class DefaultUUIDField(models.UUIDField):

    def __init__(self, *args, **kwargs):
        kwargs['blank'] = True
        kwargs.setdefault('editable', False)
        super(DefaultUUIDField, self).__init__(*args, **kwargs)

    def pre_save(self, model_instance, add):
        value = super(DefaultUUIDField, self).pre_save(model_instance, add)
        if add and value is None:
            value = force_unicode(self.create_uuid())
            setattr(model_instance, self.attname, value)
            return value
        else:
            if not value:
                value = force_unicode(self.create_uuid())
                setattr(model_instance, self.attname, value)
        return value

    @staticmethod
    def create_uuid():
        return uuid.uuid4()