code: def get_unique_pathname(path, root=''):
  	
  	path = os.path.join(root, path)
  	# consider the path supplied, then the paths with numbers appended
  	potentialPaths = itertools.chain((path,), __get_numbered_paths(path))
  	potentialPaths = six.moves.filterfalse(os.path.exists, potentialPaths)
  	return next(potentialPaths)
docs: Return a pathname possibly with a number appended to it so that it is
  	unique in the directory.