Python中列表的copy方法

Python中列表的copy方法

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：

names = [‘Zhangsan’,’Lisi’,’WangErgou’]
names2 = names.copy()
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？

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

结果显而易见，复制体和本体互不影响，结果如下：

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

那么列表嵌套是否也适用呢，测试一下：

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

额，结果好像有点不同：

[‘Liuneng’,’Zhaosi’,[’SongXiaofeng’,’LiuDanaodai'],'XieGuangkun'] [‘Liuneng’,’Zhaosi’,[’SongXiaofeng’,’LiuDanaodai'],’XieGuangkun’]
[‘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：

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：

['zhao','qian',['sun','li'],'zhou’] ['zhao','qian',['sun','li'],'zhou’]
['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。