python找茬系列02--浅拷贝和深拷贝，十个人有八个人会晕！

一、概念

可变数据类型：列表list和字典dict。

不可变数据类型：整型int、浮点型float、字符串型string和元组tuple。

一、实例分析

1、可变数据类型赋值

raw = [1, 2, 3, 4]
raw.append(5)
a = raw
print('raw = ', raw)
print('a = ', a)

a.append(6)
print('raw = ', raw)
print('a = ', a)

输出结果：

raw =  [1, 2, 3, 4, 5]
a =  [1, 2, 3, 4, 5]
raw =  [1, 2, 3, 4, 5, 6]
a =  [1, 2, 3, 4, 5, 6]

可变数据赋值过程.png

结论：当给可变数据类型直接赋值时，无论赋值的对象还是被赋值的对象发生改变，两者都同时变化

2、不可变数据类型赋值

raw = 10
a = raw
print(raw)
print(a)

raw = 5
print(raw)
print(a)

a = 15
print(raw)
print(a)

输出结果：

不可变数据赋值过程.png

当给不可变数据赋值时，无论被赋值对象还是赋值对象都互不影响对方

3、浅拷贝

I、浅拷贝切片方式

raw = [1, 2, 3, 4]
a = raw[:]
print(raw)
print(a)
print("==============")
a.append(5)
print(raw)
print(a)
print("==============")
raw.append(6)
print(raw)
print(a)

输出结果：

[1, 2, 3, 4]
[1, 2, 3, 4]
==============
[1, 2, 3, 4]
[1, 2, 3, 4, 5]
==============
[1, 2, 3, 4, 6]
[1, 2, 3, 4, 5]

图.png

II、浅拷贝切片方式：调用copy模块

raw = [1, 2, 3, 4]
a = copy.copy(raw)
print(raw)
print(a)
print("==============")
a.append(5)
print(raw)
print(a)
print("==============")
raw.append(6)
print(raw)
print(a)

输出结果：

[1, 2, 3, 4]
[1, 2, 3, 4]
==============
[1, 2, 3, 4]
[1, 2, 3, 4, 5]
==============
[1, 2, 3, 4, 6]
[1, 2, 3, 4, 5]

III、浅拷贝为什么叫浅拷贝，请看下面例子

import copy

raw = [1, 2, 3, 4, ['a', 'b']]
a = copy.copy(raw)
print(raw)
print(a)
print("==============================")
raw[4].append('c')
print(raw)
print(a)
print("==============================")
a[4].append('d')
print(raw)
print(a)
print("==============================")

输出结果：

[1, 2, 3, 4, ['a', 'b']]
[1, 2, 3, 4, ['a', 'b']]
==============================
[1, 2, 3, 4, ['a', 'b', 'c']]
[1, 2, 3, 4, ['a', 'b', 'c']]
==============================
[1, 2, 3, 4, ['a', 'b', 'c', 'd']]
[1, 2, 3, 4, ['a', 'b', 'c', 'd']]
==============================

图.png

import copy

raw = [1, 2, 3, 4, ['a', 'b']]
a = copy.copy(raw)
print(raw)
print(a)
print("==============================")
raw.append(5)
print(raw)
print(a)
print("==============================")
a.append(6)
print(raw)
print(a)
print("==============================")

输出结果：

[1, 2, 3, 4, ['a', 'b']]
[1, 2, 3, 4, ['a', 'b']]
==============================
[1, 2, 3, 4, ['a', 'b'], 5]
[1, 2, 3, 4, ['a', 'b']]
==============================
[1, 2, 3, 4, ['a', 'b'], 5]
[1, 2, 3, 4, ['a', 'b'], 6]
==============================

拷贝父对象，不会拷贝对象的内部的子对象

4、深拷贝为什么叫深拷贝，请看下面例子

import copy

raw = [1, 2, 3, 4, ['a', 'b']]
a = copy.deepcopy(raw)
print(raw)
print(a)
print("==============================")
raw.append(5)
print(raw)
print(a)
print("==============================")
a.append(6)
print(raw)
print(a)
print("==============================")

输出结果：

[1, 2, 3, 4, ['a', 'b']]
[1, 2, 3, 4, ['a', 'b']]
==============================
[1, 2, 3, 4, ['a', 'b'], 5]
[1, 2, 3, 4, ['a', 'b']]
==============================
[1, 2, 3, 4, ['a', 'b'], 5]
[1, 2, 3, 4, ['a', 'b'], 6]
==============================

import copy

raw = [1, 2, 3, 4, ['a', 'b']]
a = copy.deepcopy(raw)
print(raw)
print(a)
print("==============================")
raw[4].append('c')
print(raw)
print(a)
print("==============================")
a[4].append('d')
print(raw)
print(a)
print("==============================")

输出结果：

[1, 2, 3, 4, ['a', 'b']]
[1, 2, 3, 4, ['a', 'b']]
==============================
[1, 2, 3, 4, ['a', 'b', 'c']]
[1, 2, 3, 4, ['a', 'b']]
==============================
[1, 2, 3, 4, ['a', 'b', 'c']]
[1, 2, 3, 4, ['a', 'b', 'd']]
==============================

图.png

copy 模块的 deepcopy 方法，完全拷贝了父对象及其子对象。

二、赠语

黑发不知勤学早，白首方悔读书迟。

最后编辑于：2019.08.02 09:41:52