Palindrome number program in Python

A palindrome number reads the same from left to right and from right to left. 121, 4554 and 7 are palindromes. 123 is not.

The program

n = int(input("Enter a number: "))

text = str(n)
if text == text[::-1]:
    print(f"{n} is a palindrome")
else:
    print(f"{n} is not a palindrome")

Typed in this example: 12321. Press Run to type your own.

Enter a number: 12321
12321 is a palindrome

How it works

• str(n) turns the number into a string, such as "12321".
• text[::-1] is the same string reversed. If the string and its reverse are equal, the number is a palindrome.
• Negative numbers are never palindromes with this rule: "-121" reversed is "121-". This is the usual convention.

Another way: without strings

This version reverses the digits with arithmetic, as on the reverse a number page, and compares the result with the original:

def is_palindrome(n):
    if n < 0:
        return False
    original = n
    reversed_number = 0
    while n > 0:
        reversed_number = reversed_number * 10 + n % 10
        n //= 10
    return reversed_number == original


for n in [121, 4554, 123, 7, 10, -121]:
    print(n, is_palindrome(n))

121 True
4554 True
123 False
7 True
10 False
-121 False

• The loop changes n, so the function saves the starting value in original first.
• 10 is a good test case: reversed, it becomes 1 (the zero is lost), and 1 is not equal to 10, so the answer is correctly False.

Related programs: Palindrome string.