def __init__(self, start_time, end_time):
    self._start_time = None
    self._end_time = None
    if (end_time > start_time):
        self._start_time = start_time
        self._end_time = end_time
    else:
        raise ValueError('Time Error')
def __init__(self, start_time, end_time):
    self._start_time = None
    self._end_time = None
    if (end_time > start_time):
        self._start_time = start_time
        self._end_time = end_time
    else:
        raise ValueError('Time Error')