Valid Palindrome

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

My solution:

class Solution:
    def isPalindrome(self, s):
        """
        :type s: str
        :rtype: bool
        """
        size_s = len(s)
        start = 0
        end = size_s - 1

        while start < end:
            while start < end and not s[start].isalnum():
                start += 1

            while start < end and not s[end].isalnum():
                end -= 1

            if s[start].lower() != s[end].lower():
                return False

            start += 1
            end -= 1

        return True

check out isalnum() function.

isalnum means alphabet + number

https://www.tutorialspoint.com/python/string_isalnum.htm