Turtle.py atop pygame

My 50-examples book uses the standard library's turtle.py module for graphics. I'd like my examples to work on a Raspberry Pi as smoothly as possible. But turtle.py is written on top of Tkinter, which adds an extra layer and requires running X instead of starting from the Pi's console.

In theory, turtle.py should be portable to a different graphics subsystem. I've therefore created a game-turtle repository on Github and will try to implement the necessary classes using PyGame.