input: def reverse_words(str: str) -> str:
      """ Reverse the order of words in a given string.
      >>> reverse_words("hello world")
      'world hello'
      >>> reverse_words("Python programming is fun")
      'fun is programming Python'
      """
      return " ".join(str.split()[::-1])
output:     return " ".join(str.split()[::-1])