code: def graph_path_length(self, node_source, node_target):
          
  
          length = 0
          path = self.find_path(node_source, node_target)
          node_pairs = list(zip(path[0:len(path)-1], path[1:len(path)]))
  
          for n1, n2 in node_pairs:
              length += self._graph.adj[n1][n2]['branch'].length
  
          return length
docs: Calculates the absolute distance between `node_source` and `node_target` in meters using find_path() and branches' length attribute.
  
          Args
          ----
          node_source: GridDing0
              source node, member of _graph
          node_target: GridDing0
              target node, member of _graph
  
          Returns
          -------
          float
              path length in m