def METHOD_NAME(self):
    """
    Returns:
        (bool): True for on, False for off.
    Raises:
        ValueError: When tell is_on for unknown cases.
    """
    if self.val in ['Y', '1']:
        return True
    if self.val in ['N', '0']:
        return False
    raise ValueError("Unexpected value {0}, please get raw data from attribute 'val' and tell is_on by yourself.".format(self.val))