docs: def to_gzipped_file(data, out=None):
      """
      Pack `data` to GZIP and write them to `out`. If `out` is not defined,
      :mod:`stringio` is used.
  
      Args:
          data (obj): Any packable data (str / unicode / whatever).
          out (file, default None): Optional opened file handler.
  
      Returns:
          obj: File handler with packed data seeked at the beginning.
      """
      if not out:
          out = StringIO.StringIO()
  
      with gzip.GzipFile(fileobj=out, mode="w") as f:
          f.write(data)
  
      out.seek(0)
      return out