Classic palindrome phrase
Input
is_palindrome('A man, a plan, a canal: Panama')
Output
True
Ignoring non-alphanumeric characters and case, the string becomes 'amanaplanacanalpanama', which is the same forwards and backwards.
Full lesson preview
Check Palindrome with Loop
Determine whether a string is a palindrome using explicit loops and ignoring non-alphanumeric characters.
Python practice18 minLoops & IterationIntermediateLast updated March 15, 2026
Problem statement
Write is_palindrome(s) that returns True if the string s is a palindrome when considering only alphanumeric characters and ignoring case, otherwise return False. Use loops (for or while) to compare characters; do not use slicing like s[::-1] or the reversed() built-in for the main comparison logic.
Examples of treatment:
- 'A man, a plan, a canal: Panama' -> True
- 'race a car' -> False
- Empty string or strings with no alphanumeric characters are palindromes (return True).
Task
Implement a function that checks if a string reads the same forwards and backwards, ignoring case and non-alphanumeric characters, using loops (no slicing for reversal).
Examples
Input format
A single argument: s (string).
Output format
Boolean True if palindrome according to the rules, otherwise False.
Constraints
String length <= 1000. Use explicit loops for comparison; you may use str.isalnum() and str.lower().
Samples
Sample 1
Input
is_palindrome('Racecar')
Output
True
Case-insensitive palindrome.