input: Write a function to check if a given string is a palindrome. If the input string is a palindrome, the function should return True; otherwise, it should return False. If the input string is empty, it should also return True, as an empty string is considered a palindrome.
  def is_palindrome(s):
      '''This function returns True if the string s is a palindrome and False if it isn't.'''
      return s == s[::-1]
  
  assert is_palindrome("")==True
  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")==False
output: def is_palindrome(s):
      s = ''.join(filter(str.isalnum, s)).lower()
      return s == s[::-1]