input: Write a function to determine if a given string is a palindrome. If the string reads the same forwards and backwards, the function should return True, otherwise it should return False. If the string is empty, return True.
  assert is_palindrome("racecar") == True
  assert is_palindrome("hello") == False
  assert is_palindrome("madam") == True
  assert is_palindrome("abba") == True
  assert is_palindrome("") == True
output: def is_palindrome(s):
      return s == s[::-1]