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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _clear_expired_zones(self):
 """ Update zone status for all expired zones. """

        zones = []

        for z in list(self._zones.keys()):
            zones += [z]

        for z in zones:
            if self._zones[z].status != Zone.CLEAR and self._zone_expired(z):
                self._update_zone(z, Zone.CLEAR)