Reading and writing files in python

on
file_system_read_write_file

Skill - Reading and writing files in python

Table of Contents

Skills Required

Please make sure to have all the skills mentioned above to understand and execute the code mentioned below. Go through the above skills if necessary for reference or revision

In this post, we will learn to read and write files in python

Open a file using ‘open’ function

Opening a file is required for reading or writing to a file

with open("test.txt",'w',encoding = 'utf-8') as f:
   # perform operations on the file

In the above example we use the filename input of open function as ‘test.txt’, means that the file should be in the same folder of python script file

We can also give absolute file paths like the example below

with open(r"C:\Users\Nagasudhir\Documents\test.txt") as t:

file mode in ‘open’ function

By default, the open function opens the file only for reading, i.e., read mode.
The mode of file opening can be specified using the mode input of the function. The main file open mode options are as shown below

  • ‘r’ , for reading.
  • ‘w’ , for writing (clears any previous file data).
  • ‘a’ , for appending (adding new data at the end of file).
  • ‘r+’ , for both reading and writing while preserving the old data
  • ‘w+’ , for both reading and writing while erasing the old data

writing to file using ‘w’ file mode

# open the file in write mode using mode='w'
with open(r"C:\Users\Nagasudhir\Documents\test.txt", mode='w') as f:   
   f.write("The first line\n")
   f.write("This is the second line\nThis the third line")

The \n character will create a new line in the file as shown above.
It is also worth noting that mode='w' or mode = 'w+' will create the file if it does not exist.

read the whole file content using ‘read’ function

# open the file for reading
with open(r"C:\Users\Nagasudhir\Documents\test.txt", mode='r') as f:
   # read all the file content   
   fStr = f.read()
   # please note that once again calling f.read() will return empty string
   
   print(fStr)
   # this will print the whole file contents

read each line file content using a for loop

# open the file for reading
with open(r"C:\Users\Nagasudhir\Documents\test.txt", mode='r') as f:
   for ln in f:
      print(ln, end='')
      # this the line, end='' will avoid extra line in console

load all the lines of a file into an array using ‘readlines’ function

with open(r"C:\Users\Nagasudhir\Documents\test.txt", mode='r') as f:
   # load all the lines of the file into an array
   textLines = f.readlines()
   
   print(textLines)
   # this will print 
   # ['The first line\n', 'This is the second line\n', 'This the third line']

Video

The video for this post can be seen here

Online Interpreter

Although we recommend to practice the above examples in Visual Studio Code, you can run these examples online at https://www.tutorialspoint.com/execute_python_online.php

References

Table of Contents

Comments

Post a Comment