code: def _get_and_set_reconnection_handler(self, new_handler):
          
          with self._reconnection_lock:
              old = self._reconnection_handler
              self._reconnection_handler = new_handler
              return old
docs: Called by the _ControlReconnectionHandler when a new connection
          is successfully created.  Clears out the _reconnection_handler on
          this ControlConnection.