input: Write a python function to check if a string is a palindrome, ignoring punctuation and case sensitivity.
  assert is_palindrome("A man, a plan, a canal: Panama") == True
  assert is_palindrome("racecar") == True
  assert is_palindrome("hello") == False
  assert is_palindrome("Was it a car or a cat I saw?") == True
output: def is_palindrome(s):
      import re
      cleaned = re.sub(r'[^A-Za-z0-9]', '', s).lower()
      return cleaned == cleaned[::-1]