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