hmm interesting, just read another article on Grok yesterday posted by a previous intern of that team.
(sadly it's in Chinese, but it covered the detail of Python Indexer's implementation)
http://blog.sina.com.cn/s/blog_5d90e82f010191rh.html
EDIT: Another article on the analyzer by this author, in English. http://yinwang0.wordpress.com/2010/09/12/pysonar/