Current version of pyusb is 1.0 alpha3. Version in tree is alpha1. At least one year older than alpha3 (released sept 2012). There seems to be substantial changes, at least with regards to software I happen to be using. (Won't work on pre-alpha2.) pyUSB website : http://sourceforge.net/apps/trac/pyusb/
added to the tree. Author has cut out some previously included content, most significantly the tests.