def _link_down(self, port):
        try:
            dst, rev_link_dst = self.links.port_deleted(port)
        except __HOLE__:
            # LOG.debug('key error. src=%s, dst=%s',
            #           port, self.links.get_peer(port))
            return
        link = Link(port, dst)
        self.send_event_to_observers(event.EventLinkDelete(link))
        if rev_link_dst:
            rev_link = Link(dst, rev_link_dst)
            self.send_event_to_observers(event.EventLinkDelete(rev_link))
        self.ports.move_front(dst)
dataset/ETHPy150Open osrg/ryu/ryu/topology/switches.py/Switches._link_down