code: def get(self, line_number):
          
          if line_number not in self._get_cache:
              self._get_cache[line_number] = self._get(line_number)
          return self._get_cache[line_number]
docs: Return the needle positions or None.
  
          :param int line_number: the number of the line
          :rtype: list
          :return: the needle positions for a specific line specified by
            :paramref:`line_number` or :obj:`None` if no were given