input: Write a python function to sort words in a string by their length in descending order.
  assert sort_words_by_length("This is the string which is to be sorted") == "string sorted which This"
  assert sort_words_by_length("Sorting words by length in descending order") == "descending Sorting length words order by in"
  assert sort_words_by_length("Write a python function") == "function python Write a"
output: def sort_words_by_length(s):
      words = s.split()
      words.sort(key=len, reverse=True)
      return ' '.join(words)