Thanks for answering,
I'll try to keep "PYTHON_SINGLE_TARGET="python3_4" in make.conf.
Commands you suggested didn't get anything to rebuild or reinstall, system is up-to date.
So, I'll wait for further updates.
Currently, xfce4-notifyd-0.3.0 fails to compile, that was part of recent regular updates,
and in log file I found this:
"No rule to make target 'themes/gtk-3.0/Default/gtk.css', needed by 'all-am'. Stop."
But before that , for some time , "Python Single_target 3_4" option in make.conf
was commented out, so almost whole system was built that way.
If anything else, I'll reinstall system, :)