class Student(object):

    def __init__(self, name, gender):

        self.name = name

        if gender == 'male' or 'female':

            self.__gender = gender

        else:

            raise ValueError('error gender')

    def get_gender(self):

        return self.__gender

    def set_gender(self, gender):

        if gender == 'male' or 'female':

            self.__gender = gender

        else:

            raise ValueError('error gender')