原型模式的目的是克隆物件 或者 副本

類似於淺拷貝和深拷貝

淺拷貝就是 副本依賴引用
深拷貝就是 完全克隆一份

以下是簡單的例子

import copy


class A:

    def __init__(self):
        self.x = 18
        self.msg = 'Hello'


class B(A):

    def __init__(self):
        A.__init__(self)
        self.y = 34

    def __str__(self):
        return '{}, {}, {}'.format(self.x, self.msg, self.y)

if __name__ == '__main__':
    b = B()
    c = copy.deepcopy(b)
    print([str(i) for i in (b, c)])
    print([i for i in (b, c)])
 

自己實現，好處是不單單 可以實現深拷貝功能，還能自定義一些 註冊 登出服務（增添和刪除功能）、

# coding: utf-8

import copy
from collections import OrderedDict


class Book:

    def __init__(self, name, authors, price, **rest):
        '''rest的例子有：出版商，長度，標籤，出版日期'''
        self.name = name
        self.authors = authors
        self.price = price      # 單位為美元
        self.__dict__.update(rest)

    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()

    def register(self, identifier, obj):
        self.objects[identifier] = obj

    def unregister(self, identifier):
        del self.objects[identifier]

    def clone(self, identifier, **attr):
        found = self.objects.get(identifier)
        if not found:
            raise ValueError('Incorrect object identifier: {}'.format(identifier))
        obj = copy.deepcopy(found)
        obj.__dict__.update(attr)
        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()