I couldn't find a minimal example of using Flask (a small web framework) with gevent-socketio (a simple way to get websockets). So this is a straight-up port of the chat example from gevent-socketio to Flask.
You'll need Flask and gevent-socketio installed. Then just run python server.py.
You can use virtualenv too, just type:
mkvirtualenv flask-chat
pip install -r requirements.txt
python server.py