Google App Engine or Django?

I've been learning Python and now I'd like to learn a Python-based web framework. I'm considering Google App Engine and Django. Which one should I choose? What are their unique features and learning curves?

Google App Engine is an infrastructure on which you can "build and host apps." Though not a web app framework itself, it does provide a simple web app framework called webapp (partially built on top of another framework WebOb).

There are numerous, detailed posts on choosing a Python-based web app framework: