class Student(object):    def __init__(self, name, gender):        self.name = name        self.__gender = gender    def get_gender(self):        return self.__gender    def set_gender(self,gender):        if gender == 'male' or gender == 'female':            self.__gender = gender        else:            raise ValueError("bad input")# 测试:bart = Student('Bart', 'male')if bart.get_gender() != 'male':    print('测试失败!')else:    bart.set_gender('female')    if bart.get_gender() != 'female':        print('测试失败!')    else:        print('测试成功!')