Python浅拷贝与深拷贝

时间:2022-05-23 #苦行僧人气:0

对列表深拷贝就是无论怎样改动新列表（单维or多维），原列表都不变。

而下面的浅拷贝，对于多维列表，只是第一维深拷贝了（嵌套的List保存的是地址，复制过去的时候是把地址复制过去了），所以说其内层的list元素改变了，原列表也会变。

一、浅拷贝（均是只对第一层进行深拷贝）

1. for循环依次赋值

old = [1, [1, 2, 3], 3]
new = []
for i in range(len(old)):
    new.append(old[i])
new[0] = 3
new[1][0] = 3
print(old)
print(new)

'''
[1, [3, 2, 3], 3]
[3, [3, 2, 3], 3]
'''

2. 使用copy()函数

old = [1,[1,2,3],3]
new = old.copy()
new[0] = 3
new[1][0] =3
print(old)
print(new)

输出：

[1, [3, 2, 3], 3]
[3, [3, 2, 3], 3]

3. 使用列表生成式

old = [1,[1,2,3],3]
new = [i for i in old]
 
new[0] = 3
new[1][0] = 3
print(old)
print(new)

输出:

[1, [3, 2, 3], 3]
[3, [3, 2, 3], 3]

4. 使用索引 [:]

old = [1,[1,2,3],3]
new = old[:]
 
new[0] = 3
new[1][0] = 3
print(old)
print(new)

输出：

[1, [3, 2, 3], 3]
[3, [3, 2, 3], 3]

浅拷贝对于单层列表就是深拷贝，如：

old = [1,2,3]
new = old[:]
new[0] = 666
print(old)
print(new)
"""
[1, 2, 3]
[666, 2, 3]
"""

二、深拷贝

使用用deepcopy()方法，才是真正的复制了一个全新的和原列表无关的：

import copy
old = [1,[1,2,3],3]
new = copy.deepcopy(old)
 
new[0] = 3
new[1][0] = 3
"""
[1, [1, 2, 3], 3]
[3, [3, 2, 3], 3]
"""

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