У меня издревле стоит в make.conf (ну, с обновлением 3_* версии ветки):
PYTHON_TARGETS="python2_7 python3_4"
PYTHON_SINGLE_TARGET="python2_7"
* It seems that you need to set USE_PYTHON to make sure that legacy
* packages will be built with respect to PYTHON_TARGETS correctly:
*
* USE_PYTHON='2.7'
*
* Please note that after changing the USE_PYTHON variable, you may need
* to run 'python-updater' to rebuild affected packages.
*
* For more information on PYTHON_TARGETS and python.eclass
* compatibility, please see the relevant Wiki article [1].
*
* [1] https://wiki.gentoo.org/wiki/Project:Python/PYTHON_TARGETS
portage, portage-utils и на всякий случай gentoo-functions с gentoolkit'ом пересобрал на активной версии питона, которая:
Available Python interpreters:
[1] python2.7
[2] python3.4 *