Ask HN: Best open source python project for beginners?

It's not an open-source project, but I've been using the following to brush up on Python and teach my daughters some programming:

http://learnpythonthehardway.org/

https://github.com/gregmalcolm/python_koans

http://projecteuler.net/

And, I am getting ready to 'port' some old AppleSoft Basic games from when I was a kid:

http://www.atariarchives.org/basicgames/