code: def is_palindrome(s):
      
      i = 0
      j = len(s)-1
      while i < j:
          while i < j and not s[i].isalnum():
              i += 1
          while i < j and not s[j].isalnum():
              j -= 1
          if s[i].lower() != s[j].lower():
              return False
          i, j = i+1, j-1
      return True
docs: :type s: str
      :rtype: bool