class Student(object):    def __init__(self, name, score):        self.name = name        self.score = score    def get_grade(self):        if 100 >= self.score >= 80:            return 'A'        elif 80 > self.score >= 60:            return 'B'        elif 60 > self.score >= 0:            return 'C'        else:            raise ValueError