input: Write a function that takes a string and determines whether it is a palindrome or not. If the given string is a palindrome return True else return False.
  assert is_palindrome("racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("madam")==True
  assert is_palindrome("level")==True
  assert is_palindrome("")==True
output: def is_palindrome(s):
      return s == s[::-1]