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.

def next_frame_id(self):
        """
        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.
        """
        # 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