code: def register_switch_address(addr, interval=None):
      
      assert len(addr) == 2
      assert ip.valid_ipv4(addr[0]) or ip.valid_ipv6(addr[0])
      ofp_handler = app_manager.lookup_service_brick(ofp_event.NAME)
      _TMP_ADDRESSES[addr] = interval
  
      def _retry_loop():
          # Delays registration if ofp_handler is not started yet
          while True:
              if ofp_handler.controller is not None:
                  for a, i in _TMP_ADDRESSES.items():
                      ofp_handler.controller.spawn_client_loop(a, i)
                      hub.sleep(1)
                  break
              hub.sleep(1)
  
      hub.spawn(_retry_loop)
docs: Registers a new address to initiate connection to switch.
  
      Registers a new IP address and port pair of switch to let
      ryu.controller.controller.OpenFlowController to try to initiate
      connection to switch.
  
      :param addr: A tuple of (host, port) pair of switch.
      :param interval: Interval in seconds to try to connect to switch