Moving to Python 3

This is why Gentoo
(a) installs python executables as /usr/bin/pythonX.Y, with /usr/bin/python2 and /usr/bin/python3 as customizeable symlinks, and /usr/bin/python as a symlink to an intelligent wrapper controlled by eselect; and
(b) provides the python_convert_shebangs() function in the python eclass, allowing ebuild writers to easily change all the "#!/usr/bin/env python*" strings in the scripts in the package to call whichever python version is appropriate for that package.