code: def next_frame_id(self):
          
          # Python 2/3 compatible way of converting 1 to "\x01" in py2 or b"\x01"
          # in py3.
          fid = bytes(bytearray((self._frame_id,)))
          self._frame_id += 1
          if self._frame_id > 0xFF:
              self._frame_id = 1
          try:
              del self._rx_frames[fid]
          except KeyError:
              pass
          return fid
docs: Gets a byte of the next valid frame ID (1 - 255), increments the
          internal _frame_id counter and wraps it back to 1 if necessary.