Calculating dependencies... done!

!!! The ebuild selected to satisfy "dev-libs/gobject-introspection" has unmet requirements.
- dev-libs/gobject-introspection-1.50.0::gentoo USE="cairo -doctool -test" ABI_X86="(64)" 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:
    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:
    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 ) test? ( cairo )

(dependency required by "sys-auth/polkit-0.113-r4::gentoo[introspection]" [installed])
(dependency required by "sys-apps/systemd-234-r2::gentoo[policykit]" [installed])
(dependency required by "sys-apps/util-linux-2.30::gentoo[-build,systemd]" [ebuild])
(dependency required by "@system" [set])
(dependency required by "@world" [argument])