I took some of Purgathofer's courses as part of my bachelor's and they were all incredibly good. Apart from being a very engaging lecturer, he did not believe in simple "all or nothing" final exams (as sadly so many other teachers do), but gave us a range of little projects and exercises over the course of the semester, many of which, if the type of exercise warranted it, we could redo if we had made any errors on our first try. Thus we were able to actually learn from our mistakes!