code: def deep_nodes(self, allnodes=None):
          
          allnodes = (allnodes or [])
          for (node, node_) in ((node, node_) for (node, node_) in\
              self.iteritems() if not node in allnodes):
              allnodes.append(node)
              node_.deep_nodes(allnodes)
          return allnodes
docs: A recursive method to return a ``list`` of *all* **node objects** 
          connected from this **toplogical node**.