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' and gender!='female':
            return 'error'
        else:
            return gender
bart = Student('Bart', 'male')
print(bart.get_gender())
print(bart.set_gender('9087'))