Python列表赋值拷贝,浅拷贝,深拷贝的区别！

赋值拷贝又称引用拷贝

本质是创建一个指向被拷贝列表的引用，他们使用的是同一块内存区域，因为无论更改其中任何一个变量,我们被拷贝的变量也会跟着改变。简单的来说,赋值拷贝,无论把列表赋值给多少个变量,这些变量指向的都是同一个列表.如下面的例子,创建一个列表list1,将list1赋值给list3,然后给list3添加一个元素9,打印list3和list1,list3增加了一个元素9,list1也增加了一个元素9.打印他们的内存地址id,id是一样的.

list1 = [1, 2, 3, 4]

list3 = list1

list3.append(9)

print(list3)

print(list1)

print(id(list1))

print(id(list3))

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<input class="pgc-img-caption-ipt" placeholder="图片描述(最多50字)" value="" style="box-sizing: border-box; outline: 0px; color: rgb(102, 102, 102); position: absolute; left: 187.5px; transform: translateX(-50%); padding: 6px 7px; max-width: 100%; width: 375px; text-align: center; cursor: text; font-size: 12px; line-height: 1.5; background-color: rgb(255, 255, 255); background-image: none; border: 0px solid rgb(217, 217, 217); border-radius: 4px; transition: all 0.2s cubic-bezier(0.645, 0.045, 0.355, 1) 0s;"></tt-image>

浅拷贝

浅拷贝:浅拷贝是一维内存拷贝【不完全拷贝】，对于多维的列表，还会有内存公用的情况。

如下面的例子,创建一个二维列表list2,将list2拷贝给list4,先打印list4,与list2的内容一样;在list4

的一为列表下标为0的位置插入元素"b",list2的二维列表末尾添加元素"a",然后打印list4,与list2,

发现list2中的一为列表没有发生变化,在二维列表的末尾也添加了一个元素"a",这就是多维列

表内存公用的情况.

list2=[1,2,3,[7,8,9]]

list4=list2.copy()

print(list4)

list4.insert(0,"b")

list4[-1].append("a")

print(list4)

print(list2)

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<input class="pgc-img-caption-ipt" placeholder="图片描述(最多50字)" value="" style="box-sizing: border-box; outline: 0px; color: rgb(102, 102, 102); position: absolute; left: 187.5px; transform: translateX(-50%); padding: 6px 7px; max-width: 100%; width: 375px; text-align: center; cursor: text; font-size: 12px; line-height: 1.5; background-color: rgb(255, 255, 255); background-image: none; border: 0px solid rgb(217, 217, 217); border-radius: 4px; transition: all 0.2s cubic-bezier(0.645, 0.045, 0.355, 1) 0s;"></tt-image>

深拷贝

深拷贝：完全内存拷贝，将多维列表中的内容递归的复制一遍，重新存储到一块新的内存空间

因此在深拷贝不会出现内存公用的情况。深度拷贝需要导入copy模块,如下面例子,将list2拷贝给

list5,在list5中下标为0的位置插入"b",二维列表末尾添加a,打印结果,只有list5发生了变化,list2 并

没有发生变化.这就是深度拷贝,完全拷贝.

import copy

list2 = [1, 2, 3, [7, 8, 9]]

list5 = copy.deepcopy(list2)

list5[-1].append("a")

list5.insert(0, "b")

print(list5)

print(list2)

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<input class="pgc-img-caption-ipt" placeholder="图片描述(最多50字)" value="" style="box-sizing: border-box; outline: 0px; color: rgb(102, 102, 102); position: absolute; left: 187.5px; transform: translateX(-50%); padding: 6px 7px; max-width: 100%; width: 375px; text-align: center; cursor: text; font-size: 12px; line-height: 1.5; background-color: rgb(255, 255, 255); background-image: none; border: 0px solid rgb(217, 217, 217); border-radius: 4px; transition: all 0.2s cubic-bezier(0.645, 0.045, 0.355, 1) 0s;"></tt-image>