Today I read a fantastic article on mark and sweep garbage collectors, and thought I'd give replicating it in python a go.
I highly recommed reading the linked article -- it's a fascinatingly brief and simple look into one of the most misunderstood concepts in computer science. And it's drop dead simple.
My python version is all but useless, unless one plans on implementing a language in python! Which I do, in the form of silica2. Hmm.