[gentoo-user] problem emerging new stable python

[allan gottlieb]

I have two systems that are close in both hardware and software.

Today I did eix-sync on each followed by
emerge --update --changed-use --with-bdeps=y @world 

On one system (dell 6430) I was presented with many packages to merge
   python-3.5.4 [ebuild NS]
   many to reinstall [ebuild R]

This was not surprising.

The other system (dell 7450) failed with the following

!!! Problem resolving dependencies for sys-process/systemd-cron from @selected
... done!

!!! The ebuild selected to satisfy "sys-process/systemd-cron" has unmet requirements.
- sys-process/systemd-cron-1.5.4::gentoo USE="-cron-boot -etc-crontab-systemd -minutely -setgid -test -yearly" ABI_X86="(64)" PYTHON_SINGLE_TARGET="python3_4 python3_5 (-pypy3) (-python3_6)" PYTHON_TARGETS="python3_5 (-pypy3) -python3_4 (-python3_6)"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( python_single_target_pypy3 python_single_target_python3_4 python_single_target_python3_5 python_single_target_python3_6 ) python_single_target_python3_4? ( python_targets_python3_4 )

  The above constraints are a subset of the following complete expression:
    exactly-one-of ( python_single_target_pypy3 python_single_target_python3_4 python_single_target_python3_5 python_single_target_python3_6 ) python_single_target_pypy3? ( python_targets_pypy3 ) python_single_target_python3_4? ( python_targets_python3_4 ) python_single_target_python3_5? ( python_targets_python3_5 ) python_single_target_python3_6? ( python_targets_python3_6 )

(dependency required by "@selected" [set])
(dependency required by "@world" [argument])

Both 6430 and 7450 have the following content in
/etc/portage/package.use/systemd-cron

# systemd-cron needs PYTHON_SINGLE_TARGET = 3.x.
sys-process/systemd-cron python_single_target_python3_4

Those files are 2+ years old on each system

I have not let the 6430 proceed with the emerge update world.

Thanks in advance for any help.
allan