6.Python深浅拷贝

Posted 2020-10-24

Python深浅拷贝

变量赋值的过程：

# -*-coding:utf-8 -*-
__author__ = ‘xiaojiaxin‘
__file_name__ = ‘shallowcopy_deepcopy‘

#当拷贝数据足够多的时候，浪费空间
# str1=[1,"jiaxin","john"]
# str2=[1,"jiaxin","john"]
# print(str1)
# print(str2)

copy方法

str1=[1,"jiaxin","john"]
str2=str1.copy()
print(str1)
print(str2)
# [1, ‘jiaxin‘, ‘john‘]
# [1, ‘jiaxin‘, ‘john‘]

str2[0]=10;
print(str1)
print(str2)
# [1, ‘jiaxin‘, ‘john‘]
# [10, ‘jiaxin‘, ‘john‘]
str3=[[1,2],"jiaxin",‘john‘]
str4=str3.copy()
print(str4)
#[[1, 2], ‘jiaxin‘, ‘john‘]
str4[1]="jiaxin01"
print(str3)     #str3不变，str4改变
print(str4)
# [[1, 2], ‘jiaxin‘, ‘john‘]
# [[1, 2], ‘jiaxin01‘, ‘john‘]

浅拷贝：

str5=[[1,2],"jiaxin",‘john‘]
str6=str5.copy()   #等价于str6=str5[:],但是不等于str6=str5  很重要！！！！
print(str5)
print(id(str5[0]))
print(str6)
print(id(str6[0]))
# [[1, 2], ‘jiaxin‘, ‘john‘]
# [[1, 2], ‘jiaxin‘, ‘john‘]
str6[0][1]=201    #str5,str6一起改变
print(str5)
print(str6)
# [[1, 201], ‘jiaxin‘, ‘john‘]
# [[1, 201], ‘jiaxin‘, ‘john‘]

深拷贝

# -*-coding:utf-8 -*-
__author__ = ‘xiaojiaxin‘
__file_name__ = ‘deep_copy‘

import copy

#深拷贝需要一个独立的模块来完成
a=[[1,2],3,4]
b=copy.deepcopy(a)
print(id(a))
print(id(b))

b[0][0]=99
print(a)
print(b)

#1080515447944
#1080515539400
# [[1, 2], 3, 4]
# [[99, 2], 3, 4]

完全赋值：
B=a情况

a=[[1,2],3,4]
b=a
print(id(a))
print(id(b))
b[0][0]=99
print(id(a))
print(id(b))
print(a)
print(b)

# 818876113416
# 818876113416
# 818876113416
# 818876113416
# [[99, 2], 3, 4]
# [[99, 2], 3, 4]

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