code: def add_gateway_router(self, router, network):
          '''
          Adds an external network gateway to the specified router
          '''
          router_id = self._find_router_id(router)
          net_id = self._find_network_id(network)
          return self.network_conn.add_gateway_router(
              router=router_id, body={'network_id': net_id}f add_gateway_router(self, router, network):
          '''
          Adds an external network gateway to the specified router
          '''
          router_id = self._find_router_id(router)
          net_id = self._find_network_id(network)
          return self.network_conn.add_gateway_router(
              router=router_id, body={'network_id': net_id})
docs: Adds an external network gateway to the specified router