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 gender')

bart = Student('Bart', 'male')

print(bart.name)

print(bart.get_gender())

bart.set_gender('female')

print(bart.get_gender())