code: def efficiency(G, u, v):
      """Returns the efficiency of a pair of nodes in a graph.
  
      The *efficiency* of a pair of nodes is the multiplicative inverse of the
      shortest path distance between the nodes [1]_. Returns 0 if no path
      between nodes.
  
      Parameters
      ----------
      G : :class:`networkx.Graph`
          An undirected graph for which to compute the average local efficiency.
      u, v : node
          Nodes in the graph ``G``.
  
      Returns
      -------
      float
          Multiplicative inverse of the shortest path distance between the nodes.
  
      Examples
      --------
      >>> G = nx.Graph([(0, 1), (0, 2), (0, 3), (1, 2), (1, 3)])
      >>> nx.efficiency(G, 2, 3)  # this gives efficiency for node 2 and 3
      0.5
  
      Notes
      -----
      Edge weights are ignored when computing the shortest path distances.
  
      See also
      --------
      local_efficiency
      global_efficiency
  
      References
      ----------
      .. [1] Latora, Vito, and Massimo Marchiori.
             "Efficient behavior of small-world networks."
             *Physical Review Letters* 87.19 (2001): 198701.
             <https://doi.org/10.1103/PhysRevLett.87.198701>
  
      """
      try:
          eff = 1 / nx.shortest_path_length(G, u, v)
      except NetworkXNoPath:
          eff = 0
      return eff
  
imports: import networkx
  from networkx.exception import NetworkXNoPath
  from ..utils import not_implemented_for
label_desc: Use image node_id 1 for calling a global function with example usage: efficiency(G, u, v) and returns: eff