Python设计模式之原型模式

原型模式学习链接

import copy
from collections import OrderedDict

class Book:
    def __init__(self, name, authors, price, **rest):
        '''rest的例子有:出版商、长度、标签、出版日期'''
        self.name = name
        self.authors = authors
        self.price = price
        self.__dict__.update(rest)      # 添加其他额外属性

    def __str__(self):
        mylist = []
        ordered = OrderedDict(sorted(self.__dict__.items()))
        for i in ordered.keys():
            mylist.append('{}: {}'.format(i, ordered[i]))
            if i == 'price':
                mylist.append('$')
            mylist.append('\n')
        return ''.join(mylist)

class Prototype:
    def __init__(self):
        self.objects = dict()    # 初始化一个原型列表

    def register(self, identifier, obj):
        # 在原型列表中注册原型对象
        self.objects[identifier] = obj

    def unregister(self, identifier):
        # 从原型列表中删除原型对象
        del self.objects[identifier]

    def clone(self, identifier, **attr):
        # 根据 identifier 在原型列表中查找原型对象并克隆
        found = self.objects.get(identifier)
        if not found:
            raise ValueError('Incorrect object identifier: {}'.format(identifier))
        obj = copy.deepcopy(found)
        obj.__dict__.update(attr)   # 用新的属性值替换原型对象中的对应属性
        return obj

def main():
    b1 = Book('The C Programming Language', ('Brian W. Kernighan', 'Dennis M.Ritchie'),
    price=118, publisher='Prentice Hall', length=228, publication_date='1978-02-22',
    tags=('C', 'programming', 'algorithms', 'data structures'))

    prototype = Prototype()
    cid = 'k&r-first'
    prototype.register(cid, b1)
    b2 = prototype.clone(cid, name='The C Programming Language(ANSI)', price=48.99, length=274, publication_date='1988-04-01', edition=2)

    for i in (b1, b2):
        print(i)
    print("ID b1 : {} != ID b2 : {}".format(id(b1), id(b2)))

if __name__ == '__main__':
    main()

输出结果

authors: ('Brian W. Kernighan', 'Dennis M.Ritchie')
length: 228
name: The C Programming Language
price: 118$
publication_date: 1978-02-22
publisher: Prentice Hall
tags: ('C', 'programming', 'algorithms', 'data structures')

authors: ('Brian W. Kernighan', 'Dennis M.Ritchie')
edition: 2
length: 274
name: The C Programming Language(ANSI)
price: 48.99$
publication_date: 1988-04-01
publisher: Prentice Hall
tags: ('C', 'programming', 'algorithms', 'data structures')

ID b1 : 42211592 != ID b2 : 42235144

淘宝,相同的商品不同的卖家就可以通过这样构造类。

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