For Python, I really like reading Kenneth Reitz' code. For example the Requests library is pretty good reading [0]. When reading code, I like to have the documentation handy as well [1].
Django does have some really clean code and it is very easy to navigate. I feel like I only grokked Django after I started going through its internals.
I also highly recommend giving Tornado[0] and Bottle[1] a read. Outside of the the web stuff, Sqlalchemy[2] is good
It's a bit old, of course, but TeX: The Program is still a fascinating read because of the exceptional attention that Knuth has paid to exposition, especially for a program that size. Besides, TeX is still being used after almost 40 years, so it's inarguable that Knuth did some things right.