流畅的python学习笔记-第8章

第8章-对象引用、可变性和垃圾回收

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浅拷贝

copy 浅复制，不会拷贝其子对象，修改子对象，将受影响

import copy
a = [1, 2, 3]
b = copy.copy(a)

print("id a=", id(a))  # id a= 1669348705224
print("id b=", id(b))  # id b= 1669348161608

print("id a 0=", id(a[0]))  # id a 0= 1586588704
print("id b 0=", id(b[0]))  # id b 0= 1586588704

a[0] = "hello"
print("new a=", a)  # new a= ['hello', 2, 3]
print("new b=", b)  # new b= [1, 2, 3]

b[0] = "world"
print("new 2 a=", a)  # new a= ['hello', 2, 3]
print("new 2 b=", b)  # new 2 b= ['world', 2, 3]

深拷贝

deepcopy 深复制，将拷贝其子对象，修改子对象，将不受影响

import copy
a = [1, 2, 3]
b = copy.deepcopy(a)

print("id a=", id(a))  # id a= 2760920581064
print("id b=", id(b))  # id b= 2760920037448

print("id a 0=", id(a[0]))  # id a 0= 1586588704
print("id b 0=", id(b[0]))  # id b 0= 1586588704

a[0] = "hello"
print("new a=", a)  # new a= ['hello', 2, 3]
print("new b=", b)  # new b= [1, 2, 3]

b[0] = "world"
print("new 2 a=", a)  # new a= ['hello', 2, 3]
print("new 2 b=", b)  # new 2 b= ['world', 2, 3]

二者区别

发现对于不可变对象，好比整数、字符串、元组、还有由这些不可变对象组成的集合对象，浅拷贝和深拷贝没有区别，都是拷贝一个新对象

二者的区别在于拷贝组合对象，好比列表中还有列表，字典中还有字典或者列表的状况时，浅拷贝只拷贝了外面的壳子，里面的元素并无拷贝，而深拷贝则是把壳子和里面的元素都拷贝了一份新的。

看一个例子：

import copy

a = [0, [1, 2], 3]
b = copy.copy(a)
c = copy.deepcopy(a)

c[1][0] = "hello"
print("a=", a)  # a= [0, [1, 2], 3]
print("c=", c)  # c= [0, ['hello', 2], 3]

b[1][0] = "world"

print("new a=", a)  # new a= [0, ['world', 2], 3]
print("new b=", b)  # new b= [0, ['world', 2], 3]

小提示：

能够利用 python在线调试进行相关调试分析