input: Write a python function that determines whether a given string reads the same forwards and backwards.
  assert is_palindrome('') == True
  assert is_palindrome('aba') == True
  assert is_palindrome('aaaaa') == True
  assert is_palindrome('zbcd') == False
  assert is_palindrome('xywyx') == True
  assert is_palindrome('xywyz') == False
  assert is_palindrome('xywzx') == False
output: def is_palindrome(s):
      return s == s[::-1]