def _convert_range(self, req_start, req_end, length): try: ranges = ranges_from_http_header("bytes=%s-%s" % ( req_start if req_start is not None else '', req_end if req_end is not None else '')) except ValueError: return (None, None) result = fix_ranges(ranges, length) if not result: return (None, None) else: return (result[0][0], result[0][1])