!!! The ebuild selected to satisfy "net-analyzer/rrdtool:=" has unmet requirements.
- net-analyzer/rrdtool-1.7.0::net-kit USE="perl python tcpd -dbi -doc -graph -lua -rados -rrdcgi -ruby -static-libs -tcl" PYTHON_SINGLE_TARGET="-python2_7 -python3_4 -python3_5" PYTHON_TARGETS="python2_7 -python3_4 -python3_5"

The following REQUIRED_USE flag constraints are unsatisfied:
python? ( exactly-one-of ( python_single_target_python2_7 python_single_target_python3_4 python_single_target_python3_5 ) )

The above constraints are a subset of the following complete expression:
python? ( exactly-one-of ( python_single_target_python2_7 python_single_target_python3_4 python_single_target_python3_5 ) python_single_target_python2_7? ( python_targets_python2_7 ) python_single_target_python3_4? ( python_targets_python3_4 ) python_single_target_python3_5? ( python_targets_python3_5 ) )

(dependency required by "app-admin/collectd-5.7.2::nokit[-collectd_plugins_rrdcached,collectd_plugins_rrdtool]" [ebuild])
(dependency required by "@selected" [set])
(dependency required by "@world" [argument])