code: def main():
      parser = argparse.ArgumentParser(
          description=(
              "Extract back-translations from the stdout of fairseq-generate. "
              "If there are multiply hypotheses for a source, we only keep the first one. "
          )
      )
      parser.add_argument(
          "--output", required=True, help="output prefix"
      )
      parser.add_argument(
          "--srclang",
          required=True,
          help="source language (extracted from H-* lines)",
      )
      parser.add_argument(
          "--tgtlang",
          required=True,
          help="target language (extracted from S-* lines)",
      )
      parser.add_argument(
          "--minlen", type=int, help="min length filter"
      )
      parser.add_argument(
          "--maxlen", type=int, help="max length filter"
      )
      parser.add_argument("--ratio", type=float, help="ratio filter")
      parser.add_argument("files", nargs="*", help="input files")
      args = parser.parse_args()
  
      def validate(src, tgt):
          srclen = len(src.split(" ")) if src != "" else 0
          tgtlen = len(tgt.split(" ")) if tgt != "" else 0
          if (
              (
                  args.minlen is not None
                  and (srclen < args.minlen or tgtlen < args.minlen)
              )
              or (
                  args.maxlen is not None
                  and (srclen > args.maxlen or tgtlen > args.maxlen)
              )
              or (
                  args.ratio is not None
                  and (
                      max(srclen, tgtlen) / float(min(srclen, tgtlen))
                      > args.ratio
                  )
              )
          ):
              return False
          return True
  
      def safe_index(toks, index, default):
          try:
              return toks[index]
          except IndexError:
              return default
  
      with open(args.output + "." + args.srclang, "w") as src_h, open(
          args.output + "." + args.tgtlang, "w"
      ) as tgt_h:
          for line in tqdm(fileinput.input(args.files)):
              if line.startswith("S-"):
                  tgt = safe_index(line.rstrip().split("\t"), 1, "")
              elif line.startswith("H-"):
                  if tgt is not None:
                      src = safe_index(line.rstrip().split("\t"), 2, "")
                      if validate(src, tgt):
                          print(src, file=src_h)
                          print(tgt, file=tgt_h)
                      tgt = None
  
label_desc: Use image node_id 1 for calling a global function with example usage: main() and returns: True, False, toks, default