The upcoming Hydro release will support Ubuntu Raring Ringtail, which
is coming out soon. In Raring, the default Python interpreter will be
python3.3. In addition, Hydro will support Ubuntu Precise and Quantal,
and python2.7 is their default interpreter.

 https://github.com/ros-infrastructure/rep/blob/master/rep-0003.rst

Python 3 migration is a very complex issue, which will affect nearly
all ROS users and developers. Tully created a rosdistro issue to
review plans for handling this migration in Hydro:

  https://github.com/ros/rosdistro/issues/506

Please comment on these plans, and how they may affect your ROS
activities. Suggestions for how best to handle this difficult
migration are particularly welcome.
--
 joq