I have used both of these (Python and HTML5) seperately, however I'm keen to use the full power of Python over the web using HTML5 to draw things and handle the client side of things. I guess I'm looking for avenues to go down in terms of implementation. Here are some things I'd like to do if possible:

Have very interactive data, which will need to processed server-side by Python but displayed and locally manipulated by HTML5 Canvas.
Clickable components on the HTML5 Canvas which will communicate with the server side.

Is there an implementation that people can recommend? I.e. would Google App Engine be any good. Django? Pyjamas?
Thanks - apologies if this seems a little vague. I'm asking before trying one path to see if there is a heads-up to save time and effort.
A viable approach for a rich client widget like this is to use a stack like:

[ your javascript user interface ]
[ a js lib for your graphics ]
backbone.js for managing your objects client side
django-tastypie for wrapping your django objects in a RESTful API
django for defining your backend
Mixing HTML5 Canvas and Python