Shallow copy and deep copy of Python

SunriseCai 2020-11-13 11:28:40
shallow copy deep copy python


This article is pure and wild , There is no reference to other people's articles or plagiarism . Insist on originality !!

Preface

This is an interview question . Please briefly Python The shallow copy and the deep copy of ?

See other people's articles , They all have pictures . Although a picture is thousands of words , But soul painters are not suitable for drawing , So here we use simple and clear sentences to explain shallow copy and deep copy .

Concept

Shallow copy and deep copy

Say first concept :

  • Shallow copy : Copy only the outermost layer of the data set , Deep data is just memory address reference , There is no copy .
  • Deep copy : Copy all data in the data set completely , Nothing more to do with the source data

Mutable and immutable objects

Here's another concept , Namely Python Of The variable object and Immutable object .

Interpretation of official documents :

  • The variable object : A mutable object can be in its id() Change the value when it is fixed ;
  • Immutable object : Objects with fixed values . Immutable objects include numbers 、 Strings and tuples . Such an object cannot be changed . If you have to store a different value , You must create a new object .
  • id(object): Function to get the memory address of an object , Function returns the unique identifier of the object , The identifier is an integer .

Personal understanding :

  • The variable object : Generally speaking, when an object changes its value , Does not change the memory address the object points to .

  • Immutable object : And The variable object contrary .

  • Shallow copy : Shallow copy is just a layer of data on the periphery , The internal data just refers to the original memory address

  • Deep copy : Copy the outer and inner elements Object itself , Not a reference to an object

  • There is no so-called deep and shallow copy of immutable data , Are references to the memory address of the source object 、 Assignments are also references to memory addresses .

Python Common data structures .

object The variable object Immutable object
Integers int
Tuples tuple
character string str
Floating point numbers float
Boolean value bool
list list
aggregate set
Dictionaries dict

Suggestions Python Official Chinese documents Systematically understand these concepts .

Here's an example , Bao understand !!!


Code example

== And is

Python Of == Is to determine whether the values of two objects are equal ,is It is to determine whether the memory addresses of two objects are equal .
Let's look at the following example .

>>>a = [1, 2, 3]
>>>b = [1, 2, 3] # Create two a、b Two lists
>>>a == b # Judge a、b Whether the values of two objects are equal
True
>>>a is b # Judge a、b Whether the memory addresses of two objects are equal
False
>>>id(a),id(b) #  Print out the memory address of two objects , Find out something different 
(2692110484296, 2692110525256)

Shallow copy

  • Copy only the outermost layer of the data set , Deep data is just memory address reference , There is no copy .

For example, a list is nested with another list :[1, 2, 3, [4, 5]]

>>>import copy # The import module
>>>a = [1, 2, 3, [4, 5]]
>>>b = copy.copy(a) # Use a shallow copy a object
>>>b # Printout b
[1, 2, 3, [4, 5]]
>>>id(a),id(b) #  Printout a、b Memory address of 
(2692110485192, 2692110468616)
>>>a is b # a and b The memory addresses of are not equal , So back False
False
>>>a[3] is idb[3] # The inner layer of the b Of [4,5] It's actually quoting a Of [4,5] Memory address , That they are equal
True
>>>a[3][1] = 10 # change a The second element of the inner list
>>>a # Printout a
[1, 2, 3, [4, 10]]
>>>b # Printout b, You can see b It also changed .
[1, 2, 3, [4, 10]]

I believe after reading the above examples , You have understood what a shallow copy is .


Deep copy

  • Deep copy : Copy all data in the data set completely , Nothing more to do with the source data .

For example, a list is nested with another list :[1, 2, 3, [4, 5]]

>>>import copy # The import module
>>>a = [1, 2, 3, [4, 5]]
>>>b = copy.deepcopy(a) # Use a deep copy a object
>>>id(a),id(b) #  Printout a、b Memory address of 
(2692110512008, 2692110620872)
>>>a is b # object a、b Memory address is different , Here for False
False
>>>a[3] is b[3] # The inner address of the object is not the same , Here for False
False
>>>a[3][1] = 10 # change a The second element of the inner list
>>>a # Printout a
[1, 2, 3, [4, 10]]
>>>b # Printout b, You can see b It didn't change with it
[1, 2, 3, [4, 5]]

I believe you can understand the shallow copy and the deep copy here .


The article is very delicious , Don't spray .
The intention is to introduce shallow copy and deep copy in simple and clear words , I didn't expect that it was very wordy .
But long winded is long winded , Take a note .

Words behind

Okay , This sharing is over .
If you have any questions, please leave a message below .

版权声明
本文为[SunriseCai]所创,转载请带上原文链接,感谢

  1. 利用Python爬虫获取招聘网站职位信息
  2. Using Python crawler to obtain job information of recruitment website
  3. Several highly rated Python libraries arrow, jsonpath, psutil and tenacity are recommended
  4. Python装饰器
  5. Python实现LDAP认证
  6. Python decorator
  7. Implementing LDAP authentication with Python
  8. Vscode configures Python development environment!
  9. In Python, how dare you say you can't log module? ️
  10. 我收藏的有关Python的电子书和资料
  11. python 中 lambda的一些tips
  12. python中字典的一些tips
  13. python 用生成器生成斐波那契数列
  14. python脚本转pyc踩了个坑。。。
  15. My collection of e-books and materials about Python
  16. Some tips of lambda in Python
  17. Some tips of dictionary in Python
  18. Using Python generator to generate Fibonacci sequence
  19. The conversion of Python script to PyC stepped on a pit...
  20. Python游戏开发,pygame模块,Python实现扫雷小游戏
  21. Python game development, pyGame module, python implementation of minesweeping games
  22. Python实用工具,email模块,Python实现邮件远程控制自己电脑
  23. Python utility, email module, python realizes mail remote control of its own computer
  24. 毫无头绪的自学Python,你可能连门槛都摸不到!【最佳学习路线】
  25. Python读取二进制文件代码方法解析
  26. Python字典的实现原理
  27. Without a clue, you may not even touch the threshold【 Best learning route]
  28. Parsing method of Python reading binary file code
  29. Implementation principle of Python dictionary
  30. You must know the function of pandas to parse JSON data - JSON_ normalize()
  31. Python实用案例,私人定制,Python自动化生成爱豆专属2021日历
  32. Python practical case, private customization, python automatic generation of Adu exclusive 2021 calendar
  33. 《Python实例》震惊了,用Python这么简单实现了聊天系统的脏话,广告检测
  34. "Python instance" was shocked and realized the dirty words and advertisement detection of the chat system in Python
  35. Convolutional neural network processing sequence for Python deep learning
  36. Python data structure and algorithm (1) -- enum type enum
  37. 超全大厂算法岗百问百答(推荐系统/机器学习/深度学习/C++/Spark/python)
  38. 【Python进阶】你真的明白NumPy中的ndarray吗?
  39. All questions and answers for algorithm posts of super large factories (recommended system / machine learning / deep learning / C + + / spark / Python)
  40. [advanced Python] do you really understand ndarray in numpy?
  41. 【Python进阶】Python进阶专栏栏主自述:不忘初心,砥砺前行
  42. [advanced Python] Python advanced column main readme: never forget the original intention and forge ahead
  43. python垃圾回收和缓存管理
  44. java调用Python程序
  45. java调用Python程序
  46. Python常用函数有哪些?Python基础入门课程
  47. Python garbage collection and cache management
  48. Java calling Python program
  49. Java calling Python program
  50. What functions are commonly used in Python? Introduction to Python Basics
  51. Python basic knowledge
  52. Anaconda5.2 安装 Python 库(MySQLdb)的方法
  53. Python实现对脑电数据情绪分析
  54. Anaconda 5.2 method of installing Python Library (mysqldb)
  55. Python implements emotion analysis of EEG data
  56. Master some advanced usage of Python in 30 seconds, which makes others envy it
  57. python爬取百度图片并对图片做一系列处理
  58. Python crawls Baidu pictures and does a series of processing on them
  59. python链接mysql数据库
  60. Python link MySQL database