I learned a lot from reading the Django codebase. I didn't read it like a book, I read parts of it as I tried to figure out how to do things in Django, but I never felt like the code was bad. This was around 5 years ago so it's possible things have gotten more convoluted since then.
If the OP wants to grok a small, discrete codebase then I agree that Django is not what he's looking for.
