Fork and code away!
You can run the development web server either via GoogleAppEngineLauncher or command line.
Command Line to start at port 8000:
Note: Assumes that GoogleAppEngineLauncher has created a symlink to dev_appserver.py
dev_appserver.py appengine_content/ --skip_sdk_update_check=yes --port=8000 --admin_port=8009
https://developers.google.com/appengine/docs/python/gettingstartedpython27/helloworld