'Clears any entries from the zone map of removed ports.'

def _free_zones_from_removed_ports(self):

    existing_ports = [self._device_key(port) for port in (list(self.filtered_ports.values()) + list(self.unfiltered_ports.values()))]
    removed = (set(self._device_zone_map) - set(existing_ports))
    for dev in removed:
        self._device_zone_map.pop(dev, None)
