How to check if a string is a palindrome in Python?

Question

Jayant Kumar · Accepted Answer

Table of Contents
Introduction:
A palindrome is a string that reads the same forward and backward, such as "radar" or "level." Checking if a string is a palindrome is a common task in string manipulation and problem-solving. Python offers several methods to determine if a string meets this criterion.
Method : Simple Reversal Comparison
One of the most straightforward methods to check for a palindrome is to compare the string with its reversed version.
Example:
def is_palindrome(s):
    return s == s[::-1]

# Example usage
print(is_palindrome("radar"))  # Output: True
print(is_palindrome("hello"))  # Output: False

s[::-1] reverses the string, and then it is compared with the original string.

Method : Iterative Comparison
Another method is to compare characters from the start and end of the string moving towards the center.
Example:
def is_palindrome(s):
    left, right = 0, len(s) - 1
    while left &#x3C; right:
        if s[left] != s[right]:
            return False
        left += 1
        right -= 1
    return True

# Example usage
print(is_palindrome("radar"))  # Output: True
print(is_palindrome("world"))  # Output: False

This method uses two pointers to compare characters from both ends.

Method : Using Built-in Functions
You can also utilize Python’s built-in functions to simplify palindrome checking.
Example:
def is_palindrome(s):
    return s == ''.join(reversed(s))

# Example usage
print(is_palindrome("radar"))  # Output: True
print(is_palindrome("python")) # Output: False

reversed(s) returns an iterator of the reversed string, and ''.join() converts it back to a string.

Method : Ignoring Case and Non-Alphanumeric Characters
For a more robust palindrome check, especially if the string may contain spaces, punctuation, or mixed case, you can preprocess the string.
Example:
import re

def is_palindrome(s):
    # Convert to lowercase and remove non-alphanumeric characters
    s = re.sub(r'[^a-zA-Z0-9]', '', s).lower()
    return s == s[::-1]

# Example usage
print(is_palindrome("A man, a plan, a canal, Panama"))  # Output: True
print(is_palindrome("No 'x' in Nixon"))  # Output: True
print(is_palindrome("Palindrome"))  # Output: False

re.sub(r'[^a-zA-Z0-9]', '', s) removes all non-alphanumeric characters.
.lower() ensures the comparison is case-insensitive.

Practical Use Cases

Text Analysis: Identifying palindromic sequences in text data.
Data Validation: Checking if data entries (like codes or identifiers) are palindromes.
Puzzles and Games: Solving problems that involve palindromic patterns.

Conclusion:
Checking if a string is a palindrome in Python can be accomplished using various methods, from simple string reversal to more advanced preprocessing techniques. Each method offers different advantages depending on the requirements, such as handling mixed cases or ignoring non-alphanumeric characters. By choosing the appropriate method, you can efficiently determine if a string reads the same forward and backward in your Python programs.

How to check if a string is a palindrome in Python?

Table of Contents

Introduction:

Method : Simple Reversal Comparison

Method : Iterative Comparison

Method : Using Built-in Functions

Method : Ignoring Case and Non-Alphanumeric Characters

Conclusion:

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