How to Check if a Number is a Palindrome in Python 🐍

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Check if a Number is a Palindrome in Python

A palindrome is a number (or a word, phrase, etc.) that reads the same backward as forward. For instance, numbers like 121, 1331, and 989 are palindromes because reversing them gives the same result. In Python, checking if a number is a palindrome is a simple task. This blog will guide you through various methods to determine whether a given number is a palindrome.

What Is a Palindrome?

A number is said to be a palindrome if it remains the same when its digits are reversed. For example:

  • 121 → Reversed: 121 (Palindrome ✅)
  • 123 → Reversed: 321 (Not a Palindrome ❌)
  • 1331 → Reversed: 1331 (Palindrome ✅)

Method 1: Converting the Number to a String

One of the easiest ways to check if a number is a palindrome is by converting the number to a string, reversing the string, and comparing it with the original string.

Code Example:

# Program to check if a number is a palindrome by converting to a string

# Step 1: Define a function to check if the number is a palindrome
def is_palindrome(n):
    # Convert the number to a string
    original = str(n)
    # Reverse the string
    reversed_num = original[::-1]

    # Step 2: Check if the original string is equal to the reversed string
    return original == reversed_num

# Step 3: Test the function
number = 121
if is_palindrome(number):
    print(f"{number} is a palindrome")
else:
    print(f"{number} is not a palindrome")

Explanation:

  1. String Conversion: We convert the number to a string using str().
  2. Reversing the String: The string slicing technique [::-1] is used to reverse the string.
  3. Comparison: We compare the original string with the reversed string. If they are equal, the number is a palindrome.
  4. Output: The result is printed based on the comparison.

Output:

121 is a palindrome

Method 2: Using Mathematical Operations (Without Converting to String)

If you want to check if a number is a palindrome without converting it to a string, you can use mathematical operations to reverse the digits and compare them.

Code Example:

# Program to check if a number is a palindrome using mathematical operations

# Step 1: Define a function to reverse the number
def is_palindrome(n):
    original = n
    reversed_num = 0

    # Step 2: Reverse the digits of the number
    while n > 0:
        digit = n % 10  # Get the last digit
        reversed_num = reversed_num * 10 + digit  # Append the digit to the reversed number
        n = n // 10  # Remove the last digit from the original number

    # Step 3: Check if the reversed number is equal to the original number
    return original == reversed_num

# Step 4: Test the function
number = 1331
if is_palindrome(number):
    print(f"{number} is a palindrome")
else:
    print(f"{number} is not a palindrome")

Explanation:

  1. Digit Extraction: We use the modulo operator (%) to extract the last digit of the number.
  2. Reversing the Number: We build the reversed number by appending each extracted digit to reversed_num.
  3. Removing Digits: After extracting each digit, we divide the number by 10 to remove the last digit.
  4. Comparison: We compare the original number with the reversed number. If they match, the number is a palindrome.
  5. Output: The result is printed based on the comparison.

Output:

1331 is a palindrome

Method 3: Checking Palindrome Using Recursion

Recursion is another way to check if a number is a palindrome, although it’s less efficient than the previous methods. We can recursively break down the problem and check the first and last digits of the number.

Code Example:

# Program to check if a number is a palindrome using recursion

# Step 1: Define a recursive function to check palindrome
def is_palindrome_recursive(n, rev=0):
    if n == 0:
        return rev

    rev = rev * 10 + n % 10  # Reverse the number step by step
    return is_palindrome_recursive(n // 10, rev)

# Step 2: Test the function
number = 1221
if number == is_palindrome_recursive(number):
    print(f"{number} is a palindrome")
else:
    print(f"{number} is not a palindrome")

Explanation:

  1. Recursive Function: The function is_palindrome_recursive() reverses the number step by step.
  2. Base Case: When the number reaches zero, the reversed number is returned.
  3. Recursive Call: We recursively append each last digit to rev and reduce the number.
  4. Comparison: The final reversed number is compared with the original number to check if it is a palindrome.

Output:

1221 is a palindrome

Method 4: Using List Comparison

If you like working with lists, you can convert the digits of the number into a list and compare it with the reversed list.

Code Example:

# Program to check if a number is a palindrome using list comparison

# Step 1: Define a function to check palindrome using list comparison
def is_palindrome(n):
    # Convert the number into a list of digits
    digits = list(str(n))
    # Step 2: Compare the list with its reversed version
    return digits == digits[::-1]

# Step 3: Test the function
number = 989
if is_palindrome(number):
    print(f"{number} is a palindrome")
else:
    print(f"{number} is not a palindrome")

Explanation:

  1. List Conversion: We convert the number into a list of digits by first converting it to a string, and then using list().
  2. Comparison: We compare the original list of digits with the reversed version of the list.
  3. Output: The result is printed based on the comparison.

Output:

989 is a palindrome

Conclusion

In this blog, we covered several methods to check if a number is a palindrome in Python:

  1. String Conversion: Convert the number to a string and compare it with its reverse.
  2. Mathematical Operations: Reverse the number using arithmetic and compare the original and reversed numbers.
  3. Recursion: Use recursive function calls to reverse the number and check if it’s a palindrome.
  4. List Comparison: Convert the number into a list of digits and compare it with the reversed list.

Each method has its own advantages and trade-offs. Choose the one that best suits your needs! Keep practicing, and you’ll master these techniques in no time.

Stay tuned for more Python tutorials! 😊

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