I just ran emerge --sync on a stable amd64 machine followed by emerge -auDNv world. The machine had Python 3.3 installed but not 3.4 yet (the eselect news note about Python 3.4 came out with the emerge --sync). Portage wants to rebuild packages for Python 3.4 before it installs Python 3.4. Here's the output: alculating dependencies... done! [ebuild R ] sys-apps/file-5.22::gentoo USE="zlib -python -static-libs" ABI_X86="(64) -32 (-x32)" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild U ] sys-apps/attr-2.4.47-r2::gentoo [2.4.47-r1::gentoo] USE="-nls -static-libs" ABI_X86="(64) -32 (-x32)" 0 KiB [ebuild R ] sys-libs/libcap-ng-0.7.4::gentoo USE="-python -static-libs" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild U ] sys-apps/man-pages-4.00::gentoo [3.83::gentoo] USE="-nls" LINGUAS="-da -de -fr -it -ja -nl -pl -ro -ru -zh_CN" 1,337 KiB [ebuild U ] virtual/cron-0-r1::gentoo [0::gentoo] 0 KiB [ebuild R ] sys-apps/util-linux-2.25.2-r2::gentoo USE="caps cramfs ncurses pam suid tty-helpers unicode -fdformat -nls -python (-selinux) -slang -static-libs -systemd {-test} -udev" ABI_X86="(64) -32 (-x32)" PYTHON_SINGLE_TARGET="python2_7 -python3_3 -python3_4" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild R ] sys-apps/kmod-20::gentoo USE="tools zlib -debug -doc -lzma -python -static-libs" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild NS ] dev-lang/python-3.4.1:3.4::gentoo [2.7.9-r1:2.7::gentoo, 3.3.5-r1:3.3::gentoo] USE="gdbm ipv6 ncurses readline ssl threads xml -build -examples -hardened -sqlite -tk -wininst" 13,806 KiB [ebuild R ] dev-libs/libxml2-2.9.2-r1:2::gentoo USE="ipv6 python readline -debug -examples -icu -lzma -static-libs {-test}" ABI_X86="(64) -32 (-x32)" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild R ] dev-python/setuptools-12.0.1::gentoo USE="{-test}" PYTHON_TARGETS="python2_7 python3_4* (-pypy) (-pypy3) -python3_3*" 0 KiB [ebuild R ] sys-process/iotop-0.6::gentoo PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild R ] dev-python/dbus-python-1.2.0-r1::gentoo USE="-doc -examples {-test}" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild R ] dev-python/pycurl-7.19.3.1-r2::gentoo USE="ssl -examples {-test}" CURL_SSL="openssl -gnutls -nss" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild R ] dev-python/pyxattr-0.5.3::gentoo USE="-doc {-test}" PYTHON_TARGETS="python2_7 python3_4* (-pypy) -python3_3*" 0 KiB [ebuild R ] sys-apps/portage-2.2.20::gentoo USE="(ipc) xattr -build -doc -epydoc (-selinux)" LINGUAS="-ru" PYTHON_TARGETS="python2_7 python3_4* (-pypy) -python3_3*" 0 KiB [ebuild R ] dev-python/lxml-3.4.1::gentoo USE="threads -beautifulsoup3 -doc -examples" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB [ebuild R ] app-portage/gentoolkit-0.3.0.9-r2::gentoo PYTHON_TARGETS="python2_7 python3_4* (-pypy) -python3_3*" 0 KiB [ebuild R ] app-admin/webapp-config-1.53-r2::gentoo USE="portage" PYTHON_TARGETS="python2_7 python3_4* (-pypy) -python3_3*" 0 KiB [ebuild R ] app-editors/vim-7.4.273::gentoo USE="-X -acl -cscope -debug -gpm -lua -luajit -minimal -nls -perl -python -racket -ruby (-selinux) -tcl -vim-pager" PYTHON_SINGLE_TARGET="python2_7 -python3_3 -python3_4" PYTHON_TARGETS="python2_7 python3_4* -python3_3*" 0 KiB
Those packages that it wants to rebuild before python:3.4 is installed don't actually require python unless USE="python" is enabled, but you can see that USE="-python" is set for all of them.