How to Deserialize JSON back to objects created from db.Model

Question

I want to do something like this guy asked, but I want to deserialize instead of serialize. http://stackoverflow.com/questions/2114659/how-to-serialize-db-model-objects-to-json

Is there a library for this? I'm running Google App Engine, and I'm getting a JSON string from appengine-rest-server (http://code.google.com/p/appengine-rest-server/).

I asked the question in a different way here (http://stackoverflow.com/questions/3706208/how-to-inspect-mystery-deserialized-object-in-python) , so I'm hoping by giving the analogy reverse of the above guy's post, it will be more clear what I'm trying to do. If JSON doesn't work, I can use XML instead.