code: def make_flow_labels(graph, flow, capac):
      
      V = range(len(graph))
      arc_label = [{v:"" for v in graph[u]} for u in V]
      for u in V:
          for v in graph[u]:
              if flow[u][v] >= 0:
                  arc_label[u][v] = "%s/%s" % (flow[u][v], capac[u][v])
              else:
                  arc_label[u][v] = None   # do not show negative flow arcs
      return arc_label
docs: Generate arc labels for a flow in a graph with capacities.
  
      :param graph: adjacency list or adjacency dictionary
      :param flow:  flow matrix or adjacency dictionary
      :param capac: capacity matrix or adjacency dictionary
      :returns: listdic graph representation, with the arc label strings