You would not want to work directly with Google App Engine; which would require writing CGI code, which would be an awful lot of unnecessary work. You want to use some kind of WSGI-compatible framework like Django , web2py (as you mentioned), or webapp (a simple framework provided by Google for use with GAE).
I have no experience with webapp, but I have limited experience with Django and web2py. I have not used any of the GAE. As far as I understand, web2py supports GAE better than Django.
web2py, , , Django (, python Django). ( questions SO, ).
: web2py.