Ask HN: What's the best source to learn advanced Python?

I have completed all of the codecademy python, javascript and HTML tutorials, I've read the O'reilly's "Head first" python series and completed every other tutorial you can imagine The basics have been mastered, unfortunately there is no way for me to find out how I could build a mobile app of let's say a mail organizer or a photo sharing app The tutorials for basic python are plentiful, but is there an A to Z guide to actually build something useful using python?