I'll second the python challenge. Unlike Project Euler, this challenge required the participant to rely on finding and using some python libraries (for imaging, networking, compression, etc.) to solve the puzzles. So, not only are you researching the language to figure it out, but you're actively engaged in self-directed research to find out how to complete real tasks with python.

I've also read the "Dive Into Python" book, but that was equivalent to reading a book about an instrument without actually holding or playing one.