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【Python】copy

 3 years ago
source link: https://www.guofei.site/2018/08/06/copy.html
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【Python】copy

2018年08月06日

Author: Guofei

文章归类: Python语法 ，文章编号: 1205

版权声明：本文作者是郭飞。转载随意，但需要标明原文链接，并通知本人
原文链接：https://www.guofei.site/2018/08/06/copy.html

Edit

主要是 copy.copy 和 copy.deepcopy 的区别

copy

import copy
a=['a','b','c','d']
a_copy=copy.copy(a)
a[0]='e'

print(a,a_copy)

[‘e’, ‘b’, ‘c’, ‘d’] [‘a’, ‘b’, ‘c’, ‘d’]
a变化后，a_copy 并不跟着变化

那如果list里面包含了子列表呢

import copy
a=['a','b',['c1','c2'],'d']
a_copy=copy.copy(a)
a[2][1]='c3'

print(a,a_copy)

[‘a’, ‘b’, [‘c1’, ‘c3’], ‘d’] [‘a’, ‘b’, [‘c1’, ‘c3’], ‘d’]
为什么结果跟着变了呢，因为copy为浅copy，只复制了第一层数据，列表里存储的子列表，打印出来是子列表，其实，在内存里，列表里只是存储了子列表的内存地址，子列表在内存里是单独存储的

浅拷贝的应用举例

# 比如两口子，共有一个账号存款
import copy

card = ['name', ['saving', 100]]  # 作为一个模板
husband = copy.copy(card)
wife = copy.copy(card)
husband[0] = 'zhangsan'
wife[0] = 'fengjie'
husband[1][1] -= 20  # 丈夫取出20，还剩下80
print(husband, wife) # 两个人的账号存款同时变动

deepcopy

deepcopy可以递归地把所有数据拷贝一边。
如果数据很大，完全复制就是存储两份数据，占用内存，慎用！

import copy
a=['a','b',['c1','c2'],'d']
a_copy=copy.deepcopy(a)
a[2][1]='c3'

print(a,a_copy)

参考文献

https://docs.python.org/3/

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