code: def number_of_isolates(G):
      """Returns the number of isolates in the graph.
  
      An *isolate* is a node with no neighbors (that is, with degree
      zero). For directed graphs, this means no in-neighbors and no
      out-neighbors.
  
      Parameters
      ----------
      G : NetworkX graph
  
      Returns
      -------
      int
          The number of degree zero nodes in the graph `G`.
  
      """
      # TODO This can be parallelized.
      return sum(1 for v in isolates(G))
  
imports: import networkx
label_desc: Use image node_id 3 for calling a global function with example usage: number_of_isolates(G) and returns: sum