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