that's been the most difficult part for me, actually -- finding fun problems that I could work on that aren't completely impossible. I spent a lot of time reading books on Python when I should have just been playing with code.
I can’t say for sure how much fun this’ll be for you: The next time you think to yourself, “I wish this thing worked like this” or “I wish this thing had this feature”, if it’s open source, just load up the code and start playing with it. Your problem might be easier to solve than you’d think.
Something like SICP has problems that are fairly interesting from a mathematical perspective as well as a coding one. I don't know if there's the equivalent for Python, but it might be worth checking.