Check Palindrome in Python

Python is an object-oriented high-level programming language. Python has dynamic semantics and has high-level built-in data structures which support dynamic typing and dynamic binding. Python provides rapid development. It has an English-like syntax that is very easy to write and understand which also reduces the maintenance cost. Python is an interpreted language which means that it uses an interpreter instead of the compiler to run the code. The interpreted language is processed at the run time thus takes less time to run. Python also has third parties modules and libraries which encourage development and modifying the code.

Palindrome Overview

In this post, we are going to discuss how to check if a string is a palindrome or not. A palindrome is a set of numbers or characters that reads the same backwards as from forward. When the numbers or characters are reversed, the order remains the same. Some examples of palindromes can be Nitin, 12121, 22/02/2022.

Here Nitin is a palindrome string. A palindrome string is a palindrome of alphabets, i.e. the set of alphabets that remains the same when inverted. They can also be called symmetrical alphabets. In this example, the string is Nitin, and when we reverse it, we will still get Nitin. So it is a palindrome string.

The next example is 12121, which can be considered as a palindrome number. A palindrome number is a set of numbers that remains the same when inverted. When we reverse the number 12121, it turns out to be the exact same number 12121, so 12121 can be called a palindrome number while 12343412 cannot be considered a palindrome.

Some other examples of palindrome are:

123321, Madam, Dad, abc1221cba

In this article, we are going to check if a string is a palindrome or not in Python.

Before writing the actual code itself, it is advised to write the pseudo code or algorithm for the problem. After writing and understanding the algorithm, it becomes very easy to execute the code.

Let us try to write the pseudo code first:

Pseudo Code:

1. Input: String

2. Reverse the string using any method

3. Compare the original string with reversed string

4. If same print yes

5. Else No

We can implement different approaches while reversing the string. One point to note is to make sure to keep the data types of both strings and reversed strings the same while comparing them.

Method 1: Slicing

Our first way to reverse the original string is by using list slicing in Python.With the help of slicing, we can access a range of elements and choose where to start, where to end, and in which order.

# Program to check palindrome

str= input("Enter a string: ")

rev_str = str[::-1]

if rev_str == str:

   print("Yes, It is a palindrome")

else:

   print("No, It is not a palindrome")

Output

Enter a string: madam

Yes, It is a palindrome

In this code, we have used slicing; the syntax for the slicing is started:stop:step . We have not passed anything to start and stop, so that it will take the whole string. The step is specified as -1, which means it will process the strip backwards.

Method 2: Recursion

Our next approach to reverse the string is by using recursion. Recursion is a method of solving a problem when the problem is defined in terms of itself.

The code for recursion is:

# Checking palindrome by using recursion

def checkPalindrome(str):

   #to change it the string is similar case

   str = str.lower()

   lth = len(str)

   # if length is less than 2

if lth< 2:

         return True

   #Check if the first and last character is same

   elif str[0] == str[lth - 1]:

         # pass the string without first and last letter

         return checkPalindrome(str[1: lth - 1])

   else:

         return False

# Driver Code

str= input("Enter a string: ")

if checkPalindrome(str):

   print("Yes, It is a palindrome")

else:

   print("No, It is not a palindrome")

Output

Enter a string: 12345abccba54321

Yes, It is a palindrome

Method 3: Iteration

In this approach, we are not going to reverse the string, but we will compare the first letter to the last letter. If they are the same, then we will compare the second letter to the second last and so on. We are going to do this till we reach the middle of the string. If any character mismatches, then the string is not a palindrome, and we will break the loop.

# Iterative approach to check palindrome

def checkPalindrome(str):

   # Run loop from 0 to len/2

   lth = int(len(str))

   for i in range(0, lth/2):

         if str[i] != str[lth-i-1]:

               return False

   return True

# Driver Code

str= input("Enter a string: ")

if checkPalindrome(str):

   print("Yes, It is a palindrome")

else:

   print("No, It is not a palindrome")

Output

Enter a string: abcdefgfedcba

Yes, It is a palindrome

Method 4: Reversed function

In this method, we are going to reverse the string by using the reversed function with the join() function in Python. Reversed() function returns the reverse iteration of the string. The following python code demonstrates the process to reverse a string and check palindrome:

# Program to check palindrome using reversed function

str= input("Enter a string: ")

rev_str = ''.join(reversed(str))

if rev_str == str:

   print("Yes, It is a palindrome")

else:

   print("No, It is not a palindrome")

Note: These codes are case sensitive. If you want to ignore the case, you can convert the original string to either lowercase or uppercase using the .lower() function and then use these codes.