input: Write a function to determine if a given string is a palindrome. A palindrome is a word, phrase, number, or other sequences of characters that reads the same forward and backward (ignoring spaces, punctuation, and letter casing). Return True if the string is a palindrome and False otherwise. If the input string is empty, return True as an empty string is considered a palindrome.
  assert is_palindrome("racecar")==True
  assert is_palindrome("A man, a plan, a canal, Panama")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("Was it a car or a cat I saw?")==False
  assert is_palindrome("")==True
output: def is_palindrome(s):
      s = ''.join(e for e in s if e.isalnum()).lower()
      return s == s[::-1]