Python Program to Replace Text in a File

In this article, we are going to replace Text in a File using Python. Replacing Text could be either erasing the entire content of the file and replacing it with new text or it could mean modifying only specific words or sentences within the existing text.

Method 1: Removing all text and write new text in the same file

In this method we replacing all the text stored in the text file, for this, we will open the file in reading and writing mode and it will rewrite all the text.

# Python program to replace text in a file
s = input("Enter text to replace the existing contents:")
f = open("file.txt", "r+")
# file.txt is an example here,
# it should be replaced with the file name
# r+ mode opens the file in read and write mode
f.truncate(0)
f.write(s)
f.close()
print("Text successfully replaced")

Output: 

Enter text to replace the existing contents: Geeks
Text successfully replaced

Method 2: Using Replace function in for loop

The simple for loop is a conventional way to traverse through every line in the given text file and find the line we want to replace. Then, the desired line can be replaced by using the replace() function.  Finally, the file is opened in the write mode, and the replaced content is written in the given file.

# Python program to replace text in a file
x = input("enter text to be replaced:")
y = input("enter text that will replace:")
# file.txt should be replaced with
# the actual text file name
f = open("file.txt", "r+")
# each sentence becomes an element in the list l
l = f.readlines()
# acts as a counter to know the
# index of the element to be replaced
c = 0
for i in l:
    if x in i:
        # Replacement carries the value
        # of the text to be replaced
        Replacement = i.replace(x, y)
        # changes are made in the list
        l[c] = Replacement
    c += 1
# The pre existing text in the file is erased
f.truncate(0)
# the modified list is written into
# the file thereby replacing the old text
f.writelines(l)
f.close()
print("Text successfully replaced")

Output:

Enter text to be replaced: Geeks
Enter text that will replace: Geekforgeeks
Text successfully replaced

Method 3: Using the OS module to replace the file with new text

We use the os module to rename a new file with the original file name. In this method instead of editing the already existing file, we instead create a new file with the modified content and then delete the old file and rename the new file.

# Program to replace text in a file
import os
x = input("Enter text that will replace the existing text:")
f = open("file.txt", "r+")
f1 = open("new.txt", "r+")
f1.write(x)
os.remove("file.txt")
os.rename("new.txt", "file.txt")
f1.close()
print("File replaced")

Output:

Enter text that will replace the existing text: geeks
File replaced

Method 4: Using fileinput.input()

The fileinput.input() method gets the file as the input line by line and is mainly utilized for appending and updating the data in the given file. The fileinput and sys module need to be imported to the current Python code in order to run the code without any errors. The following code uses the fileinput.input() function for replacing the text in a line in Python.

import sys
import fileinput
x = input("Enter text to be replaced:")
y = input("Enter replacement text")
for l in fileinput.input(files = "file.txt"):
    l = l.replace(x, y)
    sys.stdout.write(l)

Output:

Enter text to be replaced: Geeks
Enter replacement text: Geeksforgeeks