As I'm sorting out how to get ROS working well with Archlinux, one of
the main issues is that 'python' is linked to python3 in arch.
There is a PEP addressing this issue in general
http://www.python.org/dev/peps/pep-0394/ which in short recommends that
python should be called via python2 or python3 unless the code is
compatible with both.