code: def push(self, nodes):
          
          if not isinstance(nodes, list):
              nodes = [nodes]
  
          for node in nodes:
              if node not in self:
                  distance = self.node.distance_to(node)
                  heapq.heappush(self.heap, (distance, node))
docs: Push nodes onto heap.
  
          @param nodes: This can be a single item or a C{list}.