def _format_buffer(buf):
    """
    example: [0x11,0x22,0x33,0x44,0x55,0x66,0x77,0x88] -> "11-22-33-44-55-66-77-88"
    :param list buf:
    :rtype: str
    """
    return '-'.join(["%.2x"%i for i in buf])