PythonWin 3.2 (r32:88445, Feb 20 2011, 21:29:02) [MSC v.1500 32 bit (Intel)] on win32.
Portions Copyright 1994-2008 Mark Hammond - see 'Help/About PythonWin' for further copyright information.
>>> import os
>>> os.makedirs("g:/a/b/c")
>>> os.listdir("g:/a")
['b']
>>> for root, dirs, files in os.walk("g:/a", topdown = False):
... 	print(root, dirs, files, os.listdir(root))
... 	os.rmdir(root)
... 	
g:/a\b\c [] [] []
g:/a\b ['c'] [] []
g:/a ['b'] [] []
>>> 

From the documentation of os.walk:
If topdown is False, the triple for a directory is generated after the triples for all of its subdirectories (directories are generated bottom-up).

As the above example shows, the directories are generated in the correct order, "generated" referring to yield from generator os.walk. However, the generated (files? and) dirs do not necessarily reflect the current situation as produced by os.listdir.

Therefore, this does not clear the entire directory tree as I would expect.

>>> os.makedirs("g:/a/b/c")
>>> for root, dirs, files in os.walk("g:/a", topdown = False):
... 	print(root, dirs, files, os.listdir(root))	
... 	if not (files + dirs):
... 	    os.rmdir(root)
... 
g:/a\b\c [] [] []
g:/a\b ['c'] [] []
g:/a ['b'] [] ['b']

I think that at least the documentation should be more clear on this issue. I would like even better, if files + dirs would match os.listdir on the moment they are generated (=yielded).