(...where "challenge" is the operative word.)
Update: In the end, after an hour of trying, I had to give in and find a clue for level 5. I missed an obvious clue, which I realised when I found this solution.
After a suggestion from SteveA in the comments to my last post, I've been working on the Python Challenge. I was quite pleased with myself for the first 4 levels, which I finished with a little bit of huffing and puffing (for example, on level 3, I was getting the right matches, but not doing the right thing with them to get the next URL). Level 5 is an utter pig. I've got so far as unpickling the data, but then I'm not 100% sure what to do with it next. It's a list of lists of tuples, which presumably map onto some data structure, but I'm not sure what. I will persist. It's pretty good fun, though I think it is perhaps overly cryptic. I think there should be slightly more clues about what to do.