I find myself doing this more and more often with python libraries, even with the well-documented ones like Django REST Framework - always keep a source browser open on the virtualenv dir so I can read library source. There's something about the style of python documentation that makes it difficult to really understand how the classes in a library fit together, so this is necessary for larger python frameworks.

(My personal gold standard for programmer reference documentation has been the Qt API docs for very, very long. They've varied in quality over the years but they're always an example of how to do it.)