Just a bitter observation...
I have found some time to take a couple of "Challenges". The results are, for the most part, "not good". I didn't know what to expect, and have been disappointed. I play on "a device" - handheld Android. This slows me up a little. I also have a hard time reading the challenge questions, which allows me a little. And, the (Python) code questions are not displayed in a monospace font, correctly formatted, which... Slows me up a little. I think you see where I'm heading with this. The challenge questions/response cycle is timed. Often, the question times out before I've even read the whole question through. Other times, I've read the question, scanned the code, gone back to re-read the question, and then have to rush an answer, because: Timer! These challenges are not good for me. They are not a good gauge of my python knowledge, my problem solving capabilities, my creative problem skills, etc. And, most important, they don't TEACH anything. They just annoy and chafe. BZZZZT! :-(