code: def _retrieve_cached_zone_variable(self, zone_id, name):
          
          try:
              s = self._zone_state[zone_id][name.lower()]
              logger.debug("Zone Cache retrieve %s.%s = %s",
                           zone_id.device_str(), name, s)
              return s
          except KeyError:
              raise UncachedVariable
docs: Retrieves the cache state of the named variable for a particular
          zone. If the variable has not been cached then the UncachedVariable
          exception is raised.