1.在列表中存在一个名为copy的方法,就像字面意思一样copy方法是用于复制列表元素的,示例如下:

1 names = [‘Zhangsan’,’Lisi’,’WangErgou’]
2 names2 = names.copy()
3 print(names,names2)

当然执行结果也跟想象中是一样的:

[‘Zhangsan’,’Lisi’,’WangErgou’] [‘Zhangsan’,’Lisi’,’WangErgou’]

如果修改了其中一项元素,会不会影响复制体呢?

1 names = [‘Zhangsan’,’Lisi’,’WangErgou’]
2 names2 = names.copy()
3 print(names,names2)
4 names[1] = “Zhaowu”
5 print(names,names2)

结果显而易见,复制体和本体互不影响,结果如下:

1 [‘Zhangsan’,’Lisi’,’WangErgou’] [‘Zhangsan’,’Lisi’,’WangErgou’]
2 [‘Zhangsan’,’Zhaowu’,’WangErgou’] [‘Zhangsan’,’Lisi’,’WangErgou’]

那么列表嵌套是否也适用呢,测试一下:

1 names = [‘Liuneng’,’Zhaosi’,[’SongXiaofeng’,’LiuDanaodai'],’XieGuangkun’]
2 names2 = names.copy()
3 print(names,names2)
4 names[2][0] = ‘XieDajiao’
5 print(names,names2)

额,结果好像有点不同:

1 [‘Liuneng’,’Zhaosi’,[’SongXiaofeng’,’LiuDanaodai'],'XieGuangkun'] [‘Liuneng’,’Zhaosi’,[’SongXiaofeng’,’LiuDanaodai'],’XieGuangkun’]
2 [‘Liuneng’,’Zhaosi’,[’XieDajiao’,’LiuDanaodai'],’XieGuangkun’] [‘Liuneng’,’Zhaosi’,[’XieDajiao’,’LiuDanaodai'],’XieGuangkun’]

原来主列表只是存储了嵌套列表在内存中的地址,而不是所看到的数据,copy的也只是嵌套列表的地址,但两个地址指向的是内存中同一块区域,所以在对嵌套列表进行修改时,只是通过了两个复制地址而修改了真实数据,所以两个列表的元素都被改掉了。

 

当然,肯定会有完全独立的复制的需求,此时则需要导入一个copy模块来实现了:

1 import copy
2 names = ['zhao','qian',['sun','li'],'zhou']
3 names2 = copy.copy(names)
4 print(names,names2)
5 names[2][0] = 'wu'
6 print(names,names2)

执行之后得到结果:

1 ['zhao','qian',['sun','li'],'zhou’] ['zhao','qian',['sun','li'],'zhou’]
2 ['zhao','qian',[‘wu','li'],'zhou’] ['zhao','qian',['wu','li'],'zhou']

-.-# 好吧,copy模块的copy方法和python列表的内置函数copy是一样的,想要完全复制则需要深层copy:

1 import copy
2 names = ['zhao','qian',['sun','li'],'zhou']
3 names2 = copy.deepcopy(names)
4 print(names,names2)
5 names[2][0] = 'wu'
6 print(names,names2)

执行之后得到结果:

1 ['zhao','qian',['sun','li'],'zhou’] ['zhao','qian',['sun','li'],'zhou’]
2 ['zhao','qian',[‘sun','li'],'zhou’] ['zhao','qian',['wu','li'],'zhou']

好了,最后终于得到的完全复制的结果。

posted on 2017-03-16 21:36  Daniel_z  阅读(7673)  评论(0编辑  收藏  举报