<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _update_zone(self, zone, status=None):
 """ Updates a zones status. :param zone: zone number :type zone: int :param status: zone status :type status: int :raises: IndexError """

        if not zone in self._zones:
            raise IndexError('Zone does not exist and cannot be updated: %d', zone)

        old_status = self._zones[zone].status
        if status is None:
            status = old_status

        self._zones[zone].status = status
        self._zones[zone].timestamp = time.time()

        if status == Zone.CLEAR:
            if zone in self._zones_faulted:
                self._zones_faulted.remove(zone)

            self.on_restore(zone=zone)
        else:
            if old_status != status and status is not None:
                self.on_fault(zone=zone)