I've been collecting eBooks from PackT publishing, and the latest free book is Scientific Computing with Python 3. They have a daily free book, and several of them are Python related, that's what stimulated my interest. If you want today's free book you've only got 7 hours to grab it, but they do cycle through the list, so it will turn up again. If you download it, don't forget to get the code file as well.

https://www.packtpub.com/packt/offers/free-learning