input: 
  def reverse_words(input_string: str) -> str:
      """ Reverse the order of words in a given string.
      >>> reverse_words("Hello world")
      "world Hello"
      >>> reverse_words("This is a test")
      "test a is This"
      """
      return " ".join(input_string.split()[::-1])
  
output:     words = input_string.split()
      reversed_words = words[::-1]
      return " ".join(reversed_words)