Generating a hash for module inheritance

models.py

from django.db import models


class Module(models.Model):
    title = models.CharField(max_length=200, blank=True, null=True)
    description = models.CharField(max_length=400, blank=True, null=True)
    parent = models.ForeignKey('self', blank=True, null=True)


    def _get_attributes(self):
        query = """SELECT T2.*,  T1.lvl
            FROM (
            SELECT
               @r AS _id,
              (SELECT @r := parent_id FROM modules_module WHERE id = _id) AS parent_id,
              @l := @l + 1 AS lvl
               FROM
                (SELECT @r := %s, @l := 0) vars,
                 modules_module m
                    WHERE @r <> 0) T1
                JOIN modules_module T2
                    ON T1._id = T2.id
                    ORDER BY T1.lvl ASC;""" % self.id

        for m in Module.objects.raw(query):
            md = m.__dict__
            remove_empty_keys(md)
            yield md

    def get_attributes(self):
        return reduce(lambda f, i: dict(i.items() + f.items()), self._get_attributes())


def remove_empty_keys(d):
    for key in d.keys():
        if d[key] is None:
            del d[key]