code: def __output_unpaired_vals(d_vals, used_ff_keys, f_f_header, sf_d, s_f_header,
                             missing_val, out_handler, outfh, delim="\t"):
    
    if missing_val is None:
      raise MissingValueError("Need missing value to output " +
                              " unpaired lines")
    for k in d_vals:
      if k not in used_ff_keys:
        f_f_flds = d_vals[k]
        if s_f_header is not None:
          s_f_flds = [dict(zip(s_f_header, [missing_val] * len(s_f_header)))]
        else:
          s_f_num_cols = len(sf_d[d_vals.keys()[0]][0])
          s_f_flds = [[missing_val] * s_f_num_cols]
        out_handler.write_output(outfh, delim, s_f_flds, f_f_flds,
                                 s_f_header, f_f_header)
docs: Use an output handler to output keys that could not be paired.
  
    Go over the keys in d_vals and for any that were not used (i.e. not in
    used_ff_keys), build an output line using the values from d_vals,
    populated the missing columns with missing_val, and output these using the
    provided output hander.