code: def write_gdf(gdf, fname):
      
      gdf_file = open(fname, 'w')
      for line in gdf:
          for i in np.arange(len(line)):
              gdf_file.write(str(line[i]) + '\t')
          gdf_file.write('\n')
      
      return None
docs: Fast line-by-line gdf-file write function
      
      
      Parameters
      ----------
      gdf : numpy.ndarray
          Column 0 is gids, columns 1: are values.
      fname : str
          Path to gdf-file.
      
      
      Returns
      -------
      None