Python Program to Reverse the Content of a File using Stack

Last Updated : 31 Dec, 2020

Given a file, the task is to print as well as store the lines of that file in reverse order using Stack.

Examples:

Input :
I am
new to this
world of
Python.

Output :
Python.
world of
new to this
I am


Input :
1
2
3
4
5
Output :
5
4
3
2
1

Approach:

Create an empty stack.
One by one push every line of the file to the stack.
One by one pop each line from the stack and put them back to the file.

Below is the implementation.

Input File:

reverse-file-python

# Python3 code to reverse the lines 
# of a file using Stack. 
   
      
# Creating Stack class (LIFO rule) 
class Stack: 
      
    def __init__(self): 
          
        # Creating an empty stack 
        self._arr = [] 
          
    # Creating push() method. 
    def push(self, val): 
        self._arr.append(val) 
   
    def is_empty(self): 
          
        # Returns True if empty 
        return len(self._arr) == 0
  
    # Creating Pop method. 
    def pop(self): 
          
        if self.is_empty(): 
            print("Stack is empty") 
            return
          
        return self._arr.pop() 
  
# Creating a function which will reverse 
# the lines of a file and Overwrites the  
# given file with its contents line-by-line 
# reversed 
def reverse_file(filename): 
       
    S = Stack() 
    original = open(filename) 
      
    for line in original: 
        S.push(line.rstrip("\n")) 
      
    original.close() 
       
       
    output = open(filename, 'w') 
      
    while not S.is_empty(): 
        output.write(S.pop()+"\n") 
      
    output.close() 
  
  
# Driver Code 
filename = "GFG.txt"
  
# Calling the reverse_file function 
reverse_file(filename) 
   
# Now reading the content of the file 
with open(filename) as file: 
        for f in file.readlines(): 
            print(f, end ="") 

Output:

Ths is a World of Geeks.
Welcome to GeeksforGeeks.

python-reverse-file-using-stack

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