开闭原则, 对扩展开放、对修改关闭

开闭原则, 对扩展开放、对修改关闭

新需求的实现是通过新增加代码来完成的，不是通过修改现有代码完成的 例如要打折了,原有的代码不修改,曾加一个派生类

只对应用程序中频繁变化的部分进行抽象 比如Book这个抽象类中的

class Book(object):
    def __init__(self, name, price, author):
        self.name = name
        self.price = price
        self.author = author

    def get_name(self):
        pass

    def get_price(self):
        pass

    def get_author(self):
        pass

    def get_book_info(self):
        pass

class NovelBook(Book):
    def __init__(self, name, price, author):
        super(NovelBook, self).__init__(name, price, author)

    def get_name(self):
        return self.name

    def get_price(self):
        return self.price

    def get_author(self):
        return self.author

    def get_book_info(self):
        return "Book name: " + self.get_name() + "  Book author: " + self.get_author() + "  Book price: " + str(self.get_price()/100.0) + "元"

class OffNovelBook(NovelBook): ### 新增子类用于扩展 
    def __init__(self, name, price, author):
        super(OffNovelBook, self).__init__(name, price, author)

    # def get_name(self):
    #     return self.name

    def get_price(self):
        origin_price = super(OffNovelBook, self).get_price()
        off_price = 0
        if origin_price >= 5000:
            off_price = origin_price * 0.8
        else:
            off_price = origin_price * 0.9

        return off_price

    # def get_author(self):
    #     return self.author

    def get_book_info(self):
        off_book_info = super(OffNovelBook, self).get_book_info()

        return off_book_info

# 此处初始化区属于高层次模块因为业务需求变更也需要相应修改，但修改越少越好
class BookStore(object):
    def __init__(self):
        self.book_list = []
        self.book_list.append(OffNovelBook("西游记", 3000, "吴承恩"))         
        self.book_list.append(OffNovelBook("三国演义", 6000, "罗贯中"))
        self.book_list.append(OffNovelBook("红楼梦", 8000, "曹雪芹"))

    def sell(self, book):
        print ("Sell Info: {}".format(book.get_book_info()))

        
if __name__ == '__main__':
    book_store = BookStore()
    for book in book_store.book_list:
        book_store.sell(book)

执行结果

Sell Info: Book name: 西游记 Book author: 吴承恩 Book price: 27.0元

Sell Info: Book name: 三国演义 Book author: 罗贯中 Book price: 48.0元

Sell Info: Book name: 红楼梦 Book author: 曹雪芹 Book price: 64.0元