input: def reverse_words(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:     words = str.split()
      reversed_words = words[::-1]
      return " ".join(reversed_words)