I can’t say these will “advance your Python skills”, but these are definitely projects that are worth a look:<p>- Django<p>- Django-Nap<p>- Django REST framework<p>- Flask<p>- Twisted<p>- Tornado<p>- Klein<p>- NumPy<p>- SciPy<p>- Pandas<p>Are they the cleanest, most beautiful codebases? Maybe not. But they tackle some interesting problems, some of them with some overlapping so you may get to see different ways/philosophies of solving the same problem, even though the Zen says there should be only one obvious way.<p>Django is a batteries-included web app framework. Flask is minimal. Tornado does async networking. Klein is like Twisted and Flask had a child (because a Klein bottle is a twisted flask). NumPy and SciPy deal with matrices and massive number crunching, leveraging Cython. Pandas deals with tabular, sometimes sparse data frames (if I remember correctly).