code: def read_neighbor_graph_pickle(gname, graph_dir):
      
      graph_path = os.path.join(graph_dir, gname+".pickle")
      if os.path.exists(graph_path):
          with open(graph_path) as handle:
              gene_graph = pickle.load(handle)
          return gene_graph
      else:
          return None
docs: Read in neighbor graph for given gene.
  
      Parameters
      ----------
      gname : str
          name of gene
      graph_dir : str
          directory containing gene graphs
  
      Returns
      -------
      gene_graph : dict or None
          neighbor graph as dict for gene. Returns None if not found.