Python - buscar las palabras no repetidas

# -*- coding: utf-8 -*-

import collections

cadena="""This eBook is for the use of anyone anywhere at no cost and with

almost no restrictions whatsoever. You may copy it, give it away or

re-use it under the terms of the Project Gutenberg License included

with this eBook or online at www.gutenberg.net

Title: The Adventures of Sherlock Holmes

Author: Arthur Conan Doyle

Posting Date: April 18, 2011 [EBook #1661]

First Posted: November 29, 2002"""

# obtenemos un array con todas las palabras

palabras=cadena.split()

# devolvemos únicamente las palabras no repetidas

print ([x for x, y in collections.Counter(palabras).items() if y == 1])