Python Program to Check Palindrome String

You can check if a string is a palindrome in Python by comparing it to its reverse using if s == s[::-1]: where s is the input string.

Examples

Inputmadam

Outputmadam is a palindrome

Inputhello

Outputhello is not a palindrome

Inputa

Outputa is a palindrome

How to Think About It

To check if a word is a palindrome, think about reading it forwards and backwards. If both are exactly the same, then the word is a palindrome. So, reverse the string and compare it with the original string.

Algorithm

1

Get the input string from the user

2

Reverse the input string

3

Compare the original string with the reversed string

4

If both are equal, print that it is a palindrome

5

Otherwise, print that it is not a palindrome

Code

python

s = input('Enter a string: ')
if s == s[::-1]:
    print(f'{s} is a palindrome')
else:
    print(f'{s} is not a palindrome')

Output

Enter a string: madam
madam is a palindrome

Dry Run

Let's trace the input 'madam' through the code

1

Input string

s = 'madam'

2

Reverse string

s[::-1] = 'madam'

3

Compare original and reversed

'madam' == 'madam' is True

4

Print result

Print 'madam is a palindrome'

Original String	Reversed String	Are Equal?
madam	madam	True

Why This Works

Step 1: Reverse the string

Using s[::-1] creates a reversed copy of the string s.

Step 2: Compare strings

If the original string and reversed string are exactly the same, it means the string reads the same forwards and backwards.

Step 3: Print result

Based on the comparison, print whether the string is a palindrome or not.

Alternative Approaches

Using a loop to compare characters

python

s = input('Enter a string: ')
flag = True
for i in range(len(s)//2):
    if s[i] != s[-(i+1)]:
        flag = False
        break
if flag:
    print(f'{s} is a palindrome')
else:
    print(f'{s} is not a palindrome')

This method manually compares characters from start and end, useful for understanding but longer code.

Using recursion

python

def is_palindrome(s):
    if len(s) <= 1:
        return True
    if s[0] != s[-1]:
        return False
    return is_palindrome(s[1:-1])
s = input('Enter a string: ')
if is_palindrome(s):
    print(f'{s} is a palindrome')
else:
    print(f'{s} is not a palindrome')

Recursive approach is elegant but less efficient for very long strings.

Complexity: O(n) time, O(n) space

Time Complexity

Reversing the string takes O(n) time where n is the string length, and comparing two strings also takes O(n). Overall O(n).

Space Complexity

Reversing the string creates a new string of length n, so space complexity is O(n).

Which Approach is Fastest?

Using slicing s[::-1] is concise and fast for most cases. The loop method uses O(1) extra space but more code. Recursion adds overhead and is less efficient.

Approach	Time	Space	Best For
String slicing (s[::-1])	O(n)	O(n)	Simple and fast for most cases
Loop character comparison	O(n)	O(1)	Memory efficient, good for large strings
Recursion	O(n)	O(n)	Elegant but less efficient for long strings