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:
I've posted it for review here:
This is in the master branch:
Released in portage-2.2.19