Management command to delete users that no longer have a reference to them (Except UserProfile and SocialData in our case).

delete_orphan_users.py

# -*- coding: utf-8 -*-
from django.core.management.base import BaseCommand
from django.contrib.auth.models import User
from emailuser.models import UserProfile
from socialdata.models import SocialData

class Command(BaseCommand):
    def _has_relations(self, related_objects, user, whitelist=(User, UserProfile, SocialData)):
        for related in related_objects:
            model = related.model
            has_subobjs = model._base_manager.filter(**{related.field.name: user}).exists()
            if model not in whitelist and has_subobjs:
                return True
        return False

    def handle(self, *args, **options):
        all_users = User.objects.filter(is_staff=False)
        print "%s users to process..." % all_users.count()
        for i, user in enumerate(all_users.iterator()):
            if i % 1000 == 0 and i != 0:
                print "%s users processed..." % i

            has_relations = self._has_relations(user._meta.get_all_related_objects(), user)
            if not has_relations:
                has_relations = self._has_relations(user._meta.get_all_related_many_to_many_objects(), user)

            if not has_relations:
                print "Deleting user: ", user
                user.delete()