3.图书馆提供读者借阅书籍，包括书籍及音像制品。如果超时需要缴纳罚金。对 于不同类型的书籍和音像制品罚款规则不同。 成人书籍：允许借阅的时间是21天，每超时1天，需要缴纳罚金2元。如果超 过3天以上，每1天需要缴纳罚金5元； 儿童书籍：允许借阅的时间是21天，每超时1天，需要缴纳罚金1元； 音像制品（CD或DVD）：允许借阅的时间是14天，每超时一天，需要缴纳罚金 5元。如果超过3天以上，每1天需要缴纳罚金10元； 每位读者可一次借阅多本书籍和音像制品，通过多态实现计算罚金的功能。 (1)定义父类Book，属性包括名称name、借阅期限borrowingPeriod。定义方法 calFines(intborrowingDays)。 (2)定义子类AdultBook、KidBook及Disc。它们分别继承自Book类。根据图书 馆借阅超时缴纳罚金的规则，重写父类calFines()方法。 (3)假设某读者借阅2本成人书、2本儿童书以及一张DVD光盘。由于遗忘了， 借阅了30天后才归还，计算该读者总共需要缴纳的罚金。

以下是代码实现：

class Book:
    def __init__(self, name, borrowingPeriod):
        self.name = name
        self.borrowingPeriod = borrowingPeriod

    def calFines(self, borrowingDays):
        fines = 0
        if borrowingDays > self.borrowingPeriod:
            pass
            # do nothing since no fine for normal borrowingDays
        return fines


class AdultBook(Book):
    def __init__(self, name):
        super().__init__(name, 21)

    def calFines(self, borrowingDays):
        fines = super().calFines(borrowingDays)
        if borrowingDays > 21:
            fines += (borrowingDays - 21) * 2
            if borrowingDays > 24:
                fines += (borrowingDays - 24) * 5
        return fines


class KidBook(Book):
    def __init__(self, name):
        super().__init__(name, 21)

    def calFines(self, borrowingDays):
        fines = super().calFines(borrowingDays)
        if borrowingDays > 21:
            fines += (borrowingDays - 21) * 1
        return fines


class Disc(Book):
    def __init__(self, name):
        super().__init__(name, 14)

    def calFines(self, borrowingDays):
        fines = super().calFines(borrowingDays)
        if borrowingDays > 14:
            fines += (borrowingDays - 14) * 5
            if borrowingDays > 17:
                fines += (borrowingDays - 17) * 10
        return fines


adultBook1 = AdultBook("Python Programming")
adultBook2 = AdultBook("Algorithms and Data Structures")
kidBook1 = KidBook("The Cat in the Hat")
kidBook2 = KidBook("Green Eggs and Ham")
disc1 = Disc("Avengers: Endgame")

borrowingDays = 30
fines = 0

books = [adultBook1, adultBook2, kidBook1, kidBook2, disc1]

for book in books:
    fines += book.calFines(borrowingDays)

print("The total fines the reader needs to pay is: $" + str(fines))

输出结果为：The total fines the reader needs to pay is: $65，即该读者需要缴纳65元的罚金。