If you wanted to write a QML / Ubuntu SDK application but had a considerable amount of python3 code that you didn't want to throw out the window you can find pyotherside utterly fantastic.
In short, you add one .so file (105K on amd64) (or install it system-wide) run qmlscene on your qml stuff and you can import and call anything from python world and get an asynchronous response. You can also use QML signals. This works pretty much like magic, it's speedy, responsive and the code is tiny. If you ever looked at pyside or pyqt then this is everything but.
I strongly recommend watching the Qt Developer Days 2013 presentation by the upstream author. You should also keep a look at the documentation. I've filed an ITP (to get it packaged in Debian) and we should see it in Debian and Ubuntu very very soon.
The upstream git repository has a number of examples. I love the matplotlib example that shows how you can render arbitrary bitmaps and push them to QML trivially.
If you want to give it a try Ive prepared a PPA with the same packages that I uploaded to Debian. Give them a spin and let me know if you find any problems.