Check Palindrome Number in Python

What You’ll Learn

A palindrome number reads the same forwards and backwards — like 121 or 7. This tutorial covers reversing digits with % 10 and // 10, listing palindromes in a range, a string alternative, a live checker, worked Python examples, edge cases, and complexity.

📝 Problem & Approach

Given a nonnegative integer, decide whether its decimal digits form a palindrome, and optionally list all palindromes in a range.

# 121 -> reverse 121 -> palindrome
# 123 -> reverse 321 -> not
# 120 -> reverse 21  -> not

Inputs & Outputs

Minimal workflow

function is_palindrome(n):
    original = n
    reversed = 0
    while n != 0:
        reversed = reversed * 10 + (n mod 10)
        n = floor(n / 10)
    return original == reversed

Method comparison

🔮 Live Preview

Enter a nonnegative integer and check whether it is a palindrome.

Press “Check palindrome”.

Examples Gallery

Three complete Python programs — arithmetic check for 121, palindromes from 100 to 200, and a string-based alternative. Click View Output to reveal sample console results.

def is_palindrome(number: int) -> bool:
    original_number = number
    reversed_number = 0

    while number != 0:
        remainder = number % 10
        reversed_number = reversed_number * 10 + remainder
        number //= 10

    return original_number == reversed_number


number = 121
if is_palindrome(number):
    print(f"{number} is a palindrome number.")
else:
    print(f"{number} is not a palindrome number.")

121 is a palindrome number.

def is_palindrome(num: int) -> bool:
    original_num = num
    reversed_num = 0

    while num != 0:
        remainder = num % 10
        reversed_num = reversed_num * 10 + remainder
        num //= 10

    return original_num == reversed_num


print("Palindrome numbers in the range 100 to 200:")
for i in range(100, 201):
    if is_palindrome(i):
        print(i, end=" ")

Palindrome numbers in the range 100 to 200:
101 111 121 131 141 151 161 171 181 191

def is_palindrome_str(number: int) -> bool:
    s = str(number)
    return s == s[::-1]


for n in (121, 123, 7, 120):
    label = "palindrome" if is_palindrome_str(n) else "not a palindrome"
    print(f"{n} is {label}.")

121 is palindrome.
123 is not a palindrome.
7 is palindrome.
120 is not a palindrome.

🔎 Worked Walkthrough — 121

Trace the reverse loop for n = 121.

original 121 equals rev 121 — palindrome.

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

Here d is the number of decimal digits in the value being tested.

💡 Best Practices