I am attempting to work with Google Checkout on Google App Engine. Currently, I am writing everything in Python and have the checkout process working. I am having some difficulty getting the notifications of processed orders functioning. I've been searching for Python examples, but thus far have been unsuccessful. Programming directly off of the documentation provided by Google, I have not been able to get my notifications working either. Would anyone happen to have a framework/demo Google Checkout Notification example in Python?
The chippyshop source has a nice example of a python Google Checkout implementation that should get you moving in the right direction.
UPDATE: I actually ended up needing to do this myself so I extended the example linked above and turned it into a reusable RequestHandler for use on GAE.
You can find the source and examples on github which should serve as a good starting point for any others following this path.