It is currently not possible to use Python with the Ubuntu SDK. The Ubuntu project is tightly focused on getting a stable mobile phone OS by October 2013, and a full convergent story by Ubuntu 14.04. In order to achieve this, QML has been the language of choice to recommend to app developers to write their software.
Technically, provided that there are Qt/QML bindings in Python available, it should be possible to use it with the SDK. However, given the time frames, we want to focus on supporting one toolkit and doing it well, rather than supporting multiple options.
If any community members are interested in contributing towards it, it should not be an impossible task, but right now the status of Python Qt bindings is a bit complicated: PySide, which would be the natural choice, will not be ported to Qt5 in the foreseeable future. PyQt has just been ported to Qt5, but it might not be the best choice in terms of licensing commercial applications, which will coexist with free, open source apps in the ecosystem. See more context on this earlier question.