Valid Palindrome

class Solution:
    def isPalindrome(self, s: str) -> bool:

        def is_alphanumeric(c: str) -> bool:
            if  ord("A") <= ord(c) <= ord("Z"):
                return True
            if ord("a") <= ord(c) <= ord("z"):
                return True
            if ord("0") <= ord(c) <= ord("9"):
                return True

            return False

        left = 0
        right = len(s) - 1

        while(left<right):
            if s[left] == " ":
                left += 1
                continue

            if s[right] == " ":
                right -= 1
                continue

            if not is_alphanumeric(s[left]):
                left += 1
                continue

            if not is_alphanumeric(s[right]):
                right -= 1
                continue

            if s[left].lower() == s[right].lower():
                left += 1
                right -= 1
            else:
                return False

        return True