# -*- coding: utf-8 -*-

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 in ['male', 'female']:

            self.__gender = gender

        else:

            raise ValueError('bad gender')

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

print(bart.get_gender())

bart.set_gender('female')

print(bart.get_gender())