docs: def iter_lines(f):
      """
      :param f:
      :type f: file
      :return:
      """
      linenum = 1
      try:
          for text in f.readlines():
              # ignore lines that consist entirely of whitespace
              if text.isspace():
                  continue
              indent,value = parse_line(text)
              yield linenum,indent,value
              linenum += 1
      except:
          raise ParserError(linenum, 0, '', 'failed to parse line')