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ceremonial Python Column No 34 piece , Classmate, stop , Don't miss this from 0 The beginning of the article ！

A lot has been written before , Are doing some data processing , But when we need to store and read data , You need documents . The school committee took you through file processing .

First learn to read and write documents ！

For example, when I was at school , The design requirement of the first programming course is to make a student management system .

This requires the use of files to handle （ You can also use a database , But in general C Language is the preferred language for many freshmen in computer department , At this time, the probability does not know the database ）.

python The most common is open and write function , as follows ：

#open function ： Receive a file name , There are other parameters that can be omitted .
one_file = open('myfile.txt')
# Read data assigned to data Variable 
data = one_file.read()

# Of a file object write function 
one_file = open('myfile.txt','w')
#write function ： Incoming data ,write Function writes data to one_file In the corresponding file .
one_file.write(' Data written to a file ')
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Let's take a look at some examples of file operations

Read file data

Keep the following data as a file ：sample.txt

 Continuous learning 
 Continuous development 
 My name is Lei Xuewei 
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afile = open("sample.txt")
print(afile.read())
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Write data and simply display

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Time : 2021/11/12 11:58  Afternoon 
# @Author : LeiXueWei
# @CSDN/Juejin/Wechat:  Lei Xuewei 
# @XueWeiTag: CodingDemo
# @File : filedemo.py
# @Project : hello

afile = open("sample.txt")
data = afile.read()
print("sample file content=", data)
afile.close()

# hold sample The read data is written to test file 
afile = open("./test.txt", "w")
afile.write(data)
afile.close()

print("write data to test file!")
afile = open("./test.txt")
data = afile.read()
afile.close()
print("test file content=", data)
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Let's see , The read content is indeed written .

The operation of this file is very simple .

Reading and writing files is so simple , But after we manipulate the file , Remember to call close function （ Close file , Otherwise, exceptions will occur in subsequent read / write operations / error ！）

close The function is called as follows ：

one_file.close() # File object .close()
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But we usually write this style of file reading and writing ：

with open('sample.txt', 'r') as one_file:
    data = one_file.read()
# No need to call close 了 , This with Within code block ,python Will help us automatically close the file .
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All the above are read at one time as soon as you open the file ,Python You can also read line by line .

According to the line read / Write data by line

According to the line read

We modified the code based on the previous read-write file , Look directly at ：

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Time : 2021/11/12 11:58  Afternoon 
# @Author : LeiXueWei
# @CSDN/Juejin/Wechat:  Lei Xuewei 
# @XueWeiTag: CodingDemo
# @File : filedemo2.py
# @Project : hello

with open("sample.txt") as afile:
    data = afile.readline()
    print("sample file content=", data)

with open("./test.txt", "w") as afile:
    afile.write(data)
    print("write data to test file!")

with open("test.txt") as afile:
    data = afile.readline()
    print("test file content=", data)
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We see here reading sample One line of the file , Then write to test file , There is only one line ！

summary

Python The reading of files is very convenient , Built in open Functions and file objects come with write function , The design is very simple .

Open the box , So simply knock , Take a few minutes to learn some file operations ！

by the way , like Python Friend, , Please pay attention to Python Basic column or Python From getting started to mastering the big column

Continuous learning and continuous development , I'm Lei Xuewei ！
Programming is fun , The key is to understand the technology thoroughly .
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