input: Write a function to determine if a given string is a palindrome. The function should convert all characters to lowercase and check if the string reads the same backward as forward. If it is a palindrome return True, otherwise return False.
  assert is_palindrome("racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("Madam")==True
  assert is_palindrome("A man, a plan, a canal, Panama")==True
  assert is_palindrome("notapalindrome")==False
output: def is_palindrome(s):
      s = ''.join(e for e in s if e.isalnum()).lower()
      return s == s[::-1]