Yes, I have learnt Python thanks to checkio.org.

By solving tasks and reading solutions afterwards I had learnt much more than from any other possible source being it books or online course.

But not only that, sometimes I got the best possible explanation via comments under given solution.

There is one more thing why one may prefer checkio over similar platforms like codefights.com. Historically, the checkio was focused on Python with possibility to import 3rd party libraries as numpy or similar. You can practice more than Python there.

Finally, the community is great.