input: Write a function to determine if a given string `s` is a palindrome. A palindrome is a string that reads the same forward and backward. If the string `s` is a palindrome, return `True`; otherwise, return `False`. If the input string is empty, return `True`.
  
  assert is_palindrome("racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("madam")==True
  assert is_palindrome("12321")==True
  assert is_palindrome("")==True
output: def is_palindrome(s):
      return s == s[::-1]