input: Write a function named is_palindrome that takes a string s as input and returns True if the string s is a palindrome (i.e., reads the same forwards and backwards), and False otherwise. If the given string is empty, the function should 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]