Python File Handling: Create, Open, Append, Read, Write

In Python, there is no need for importing external library to read and write files. Python provides an inbuilt function for creating, writing, and reading files.

In this tutorial, we will learn

• How to Open a Text File
• How to Create a Text File
• How to Append Data to a File
• How to Read a File
• How to Read a File line by line
• File Modes in Python

Syntax

file_object  = open("filename", "mode") 

Here,

• filename: gives name of the file that the file object has opened.
• mode: attribute of a file object tells you which mode a file was opened in.

More details of these modes are explained below

Step 1)

	f= open("guru99.txt","w+")

• We declared the variable f to open a file named guru99.txt. Open takes 2 arguments, the file that we want to open and a string that represents the kinds of permission or operation we want to do on the file
• Here, we used "w" letter in our argument, which indicates write and will create a file if it does not exist in library
• Plus sign indicates both read and write.

Step 2)

for i in range(10):
     f.write("This is line %d\r\n" % (i+1))

• We have a for loop that runs over a range of 10 numbers.
• Using the write function to enter data into the file.
• The output we want to iterate in the file is "this is line number", which we declare with write function and then percent d (displays integer)
• So basically we are putting in the line number that we are writing, then putting it in a carriage return and a new line character

Step 3)

	f.close() 

• This will close the instance of the file guru99.txt stored

Here is the result after code execution

When you click on your text file in our case "guru99.txt" it will look something like this

Step 1)

f=open("guru99.txt", "a+")

Once again if you could see a plus sign in the code, it indicates that it will create a new file if it does not exist. But in our case we already have the file, so we are not required to create a new file.

Step 2)

for i in range(2):
     f.write("Appended line %d\r\n" % (i+1))

This will write data into the file in append mode.

You can see the output in "guru99.txt" file. The output of the code is that earlier file is appended with new data.

Step 1) Open the file in Read mode

	f=open("guru99.txt", "r")

Step 2) We use the mode function in the code to check that the file is in open mode. If yes, we proceed ahead

	if f.mode == 'r':

Step 3) Use f.read to read file data and store it in variable content

	contents =f.read()

Step 4) print contents

Here is the output

When you run the code (f1=f.readlines()) for reading the file or document line by line, it will separate each line and present the file in a readable format. In our case the line is short and readable, the output will look similar to the read mode. But if there is a complex data file which is not readable, this piece of code could be useful.

Here is the complete code

Python 2 Example

def main():
     f= open("guru99.txt","w+")
     #f=open("guru99.txt","a+")
     for i in range(10):
         f.write("This is line %d\r\n" % (i+1))
     f.close()   
     #Open the file back and read the contents
     #f=open("guru99.txt", "r")
     #   if f.mode == 'r': 
     #     contents =f.read()
     #     print contents
     #or, readlines reads the individual line into a list
     #fl =f.readlines()
     #for x in fl:
     #print x
if __name__== "__main__":
  main()

Python 3 Example

def main():
    f= open("guru99.txt","w+")
    #f=open("guru99.txt","a+")
    for i in range(10):
         f.write("This is line %d\r\n" % (i+1))
    f.close()
    #Open the file back and read the contents
    #f=open("guru99.txt", "r")
    #if f.mode == 'r':
    #   contents =f.read()
    #    print (contents)
    #or, readlines reads the individual line into a list
    #fl =f.readlines()
    #for x in fl:
    #print(x)
if __name__== "__main__":
  main()

Summary

• Python allows you to read, write and delete files
• Use the function open("filename","w+") to create a file. The + tells the python interpreter to open file with read and write permissions.
• To append data to an existing file use the command open("Filename", "a")
• Use the read function to read the ENTIRE contents of a file
• Use the readlines function to read the content of the file one by one.