Memcache keys can't have spaces in them, so we'll remove them from the
        DN for maximum compatibility.

def _cache_key(self, attr_name):
        """
        Memcache keys can't have spaces in them, so we'll remove them from the
        DN for maximum compatibility.
        """
        dn = self._ldap_user.dn.replace(' ', '%20')
        key = u'auth_ldap.%s.%s.%s' % (self.__class__.__name__, attr_name, dn)

        return key