If deprecation warnings are enabled, then portage triggers the following warning: /usr/lib64/python3.4/formatter.py:24: PendingDeprecationWarning: the formatter module is deprecated and will be removed in Python 3.6 The PSF-2 license is compatible with the GPL-2 license, so portage can simply bundle the needed parts of the formatter module.
There's a patch in the following branch: https://github.com/zmedico/portage/tree/bug_547732 I've posted it for review here: https://archives.gentoo.org/gentoo-portage-dev/message/0f77c273a76595a3551dcfdab44291a2
This is in the master branch: https://gitweb.gentoo.org/proj/portage.git/commit/?id=971802f170e43fd36241decfa63e527dc1b3cf4f
Released in portage-2.2.19