Python problem 6 of 30

Real palindromes

Python
Easy

Write is_palindrome(s) that ignores case, spaces and punctuation, and returns True if the letters and digits read the same forwards and backwards.

is_palindrome("A man, a plan, a canal: Panama")
# True

is_palindrome("race a car")
# False

Show hint

Clean the string first with str.isalnum() and str.lower(), then compare it with its reverse.

Show solution

def is_palindrome(s):
    clean = [c.lower() for c in s if c.isalnum()]
    return clean == clean[::-1]

Filtering down to lowercase letters and digits turns the messy input into a plain sequence, then a reversed comparison does the rest. O(n) time. A two-pointer version can do it in O(1) extra space if memory matters.

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