Unfortunately, I broke the leader's confidential documents and spit blood to share the code skills of backup files

What I share today is not specific Python Knowledge point , But a very useful practical experience .

Throw questions

Let's assume such a scenario ：

• You have to write a Python Program , Every day in the morning 8 Generate or update an important document , Call 「maishu.txt」 Well .
• Suppose the file size is 100M, You may need to generate and write files 1 About minutes .
• This document is placed in a directory , Every day 24 People or other programs access and read... Every hour .

What can be done to ensure the following highlights ：

1. Ensure that this file can be used at all times , Or maximize available time .

2. If something goes wrong , You can recover immediately , Will not affect the user .

Before continuing reading , Think about it first ：「 What would you do ？」

Stupid way

First, let's talk about the practice of ordinary young people , And the worst thing to do .

Here is the pseudo code , Can not run , It is only used to explain the idea of solving the problem .

with open('maishu.txt', 'w') as f:
  #  Code logic for writing files 
  #  The write time is about one minute 

The problem with this approach is ：

• Once you start writing , The file will be emptied and gradually added , This will cause the person reading at that time to read an empty file , Or incomplete documents , Cause the reader to crash
• in other words , About 1 Minute time , This file is not available , It may cause serious errors downstream .
• If there is an error in the writing process , Can't recover instantly , It will cause system interruption , Manual intervention may be required

The major problems brought about by this approach , I've seen it several times in practical work . The file read is illegal , Read or write program crash and so on . Colleagues who make mistakes , I don't know where I am anymore .

A good way

A better way is this ：

• Write another file first , This does not affect the reading and use of the original file
• After writing , Then rename the file .

The pseudocode is as follows ：

with open('maishu20220425.txt', 'w') as f:
  #  Code logic for writing files 
  #  The write time is about one minute 
  
#  Back up the original file 
rename('maishu.txt', 'maishu20220424.txt')

#  Rename the new file to the main file 
rename('maishu20220425.txt', 'maishu.txt')

Because the last moment is just renaming the file , It's a quick process , It's not easy to make a mistake . Even if something goes wrong , You can also restore the original file . Therefore, the above problems can be well solved .

A little more improvement

Because the above backup will produce multiple files , Take up a lot of space , So the general code will only keep 5 The latest data . The pseudocode is as follows ：

with open('maishu20220425.txt', 'w') as f:
  #  Code logic for writing files 
  #  The write time is about one minute 
  
#  Back up the original file 
rename('maishu.txt', 'maishu20220424.txt')

#  Rename the new file to the main file 
rename('maishu20220425.txt', 'maishu.txt')

#  Delete the oldest backup , Keep only the latest 5 Share 
delete_backup(keep=5)

This approach is basically an industry best practice , This is done on many occasions . For example, automated deployment usually does this . In this way, the normal operation of the program will not be affected during the release process , Once something goes wrong, you can immediately roll back to the previous version .

See? ？ Next time, if you have a similar occasion , Remember to use the above method , Lest I want to show my code skills , It turned out to be self defeating

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