input: Write a function to reverse the order of words in a given string. If the input string is empty, return an empty string.
  def reverse_words(str):
      return " ".join(str.split()[::-1]) if str else ""
  
  assert reverse_words("Hello world") == "world Hello"
  assert reverse_words("Python is amazing") == "amazing is Python"
  assert reverse_words("") == ""
  assert reverse_words("SingleWord") == "SingleWord"
  assert reverse_words("With trailing spaces  ") == "spaces trailing With"
output: def reverse_words(str):
      return " ".join(str.split()[::-1]) if str else ""