code: def _write_stop_to_stop_network_edges(net, file_name, data=True, fmt=None):
      
      if fmt is None:
          fmt = "edg"
  
      if fmt == "edg":
          if data:
              networkx.write_edgelist(net, file_name, data=True)
          else:
              networkx.write_edgelist(net, file_name)
      elif fmt == "csv":
          with open(file_name, 'w') as f:
              # writing out the header
              edge_iter = net.edges_iter(data=True)
              _, _, edg_data = next(edge_iter)
              edg_data_keys = list(sorted(edg_data.keys()))
              header = ";".join(["from_stop_I", "to_stop_I"] + edg_data_keys)
              f.write(header)
              for from_node_I, to_node_I, data in net.edges_iter(data=True):
                  f.write("\n")
                  values = [str(from_node_I), str(to_node_I)]
                  data_values = []
                  for key in edg_data_keys:
                      if key == "route_I_counts":
                          route_I_counts_string = str(data[key]).replace(" ", "")[1:-1]
                          data_values.append(route_I_counts_string)
                      else:
                          data_values.append(str(data[key]))
                  all_values = values + data_values
                  f.write(";".join(all_values))
docs: Write out a network
  
      Parameters
      ----------
      net: networkx.DiGraph
      base_name: str
          path to the filename (without extension)
      data: bool, optional
          whether or not to write out any edge data present
      fmt: str, optional
          If "csv" write out the network in csv format.