Python Program for Reverse of a Number Using Type Casting

Python program to Reverse a single line of a text file

Last Updated : 25 Apr, 2025

Given a text file. The task is to reverse a single line of user's choice from a given text file and update the already existing file. Examples:

Input:
        Hello Geeks
        for geeks!

  User choice = 1

Output:
        Hello Geeks
        geeks! for

Input:
        This is a geek
        Welcome to GeeksforGeeks
        GeeksforGeeks is a computer science portal

    User choice = 0

Output:
        geek a is This
        Welcome to GeeksforGeeks
        GeeksforGeeks is a computer science portal

Implementation: Let's suppose the text file looks like this - python-reverse-text-file

Python3

# Open file in read mode
f = open('GFG.txt', 'r')

# Read the content of the
# file and store it in a list
lines = f.readlines()
    
# Close file
f.close()

# User's choice
choice = 1

# Split the line into words 
line = lines[choice].split()

# line is reversed
Reversed = " ".join(line[::-1])

# Updating the content of the
# file
lines.pop(choice)
lines.insert(choice, Reversed)

# Open file in write mode
u = open('GFG.txt', 'w')

# Write the new content in file
# and note, it is overwritten 
u.writelines(lines)
u.close()

Output: python-reverse-text-file1

Time complexity: O(n), where n is the number of lines in the file.

Auxiliary space: O(n), where n is the number of lines in the file.

Python Program for Reverse of a Number Using Type Casting

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