input: Write a function to sort words in a given string by their length in decreasing alphabetical order. If the input string is empty, return an empty string.
  
  def sort_words_by_length(my_string):
      if not my_string:
          return ""
      words = my_string.split(' ')
      words_with_length = [(len(word), word) for word in words]
      words_with_length.sort(reverse = True)
      sorted_string = " ".join([i[1] for i in words_with_length])
      return sorted_string
  
  assert sort_words_by_length("This is the string which is to be sorted")=="string sorted which This is be to the"
  assert sort_words_by_length("")==""
  assert sort_words_by_length("One two three four five")=="three five four One two"
  assert sort_words_by_length("Python programming is fun")=="programming Python fun is"
  assert sort_words_by_length("a an the")=="the an a"
output: def sort_words_by_length(my_string):
      if not my_string:
          return ""
      words = my_string.split(' ')
      words_with_length = [(len(word), word) for word in words]
      words_with_length.sort(reverse=True)
      sorted_string = " ".join([i[1] for i in words_with_length])
      return sorted_string