code: def nodes(self):
          
          return (
              devicetools.Nodes(
                  self.node_prefix+routers for routers in self._router_numbers) +
              devicetools.Node(self.last_node))
docs: A |Nodes| collection of all required nodes.
  
          >>> from hydpy import RiverBasinNumbers2Selection
          >>> rbns2s = RiverBasinNumbers2Selection(
          ...                            (111, 113, 1129, 11269, 1125, 11261,
          ...                             11262, 1123, 1124, 1122, 1121))
  
          Note that the required outlet node is added:
  
          >>> rbns2s.nodes
          Nodes("node_1123", "node_1125", "node_11269", "node_1129", "node_113",
                "node_outlet")
  
          It is both possible to change the prefix names of the nodes and
          the name of the outlet node separately:
  
          >>> rbns2s.node_prefix = 'b_'
          >>> rbns2s.last_node = 'l_node'
          >>> rbns2s.nodes
          Nodes("b_1123", "b_1125", "b_11269", "b_1129", "b_113", "l_node")