This could be a bug similair to: http://forums.gentoo.org/viewtopic-p-7215452.html

• Package: dev-libs/gobject-introspection-1.34.2-r1
• Repository: gentoo
• Maintainer: gnome@gentoo.org
• USE: elibc_glibc kernel_linux python_single_target_python2_7 python_targets_python2_7 userland_GNU x86
• FEATURES: ccache preserve-libs sandbox
• No Python implementation selected for the build. Please set
• the PYTHON_SINGLE_TARGET variable in your make.conf to one
• of the following values:
• python2_7

• ERROR: dev-libs/gobject-introspection-1.34.2-r1 failed (setup phase):
• No supported Python implementation in PYTHON_SINGLE_TARGET.
• Call stack:
• ebuild.sh, line 93: Called pkg_setup
• gobject-introspection-1.34.2-r1.ebuild, line 40: Called python-single-r1_pkg_setup
• python-single-r1.eclass, line 206: Called die
• The specific snippet of code:
• die "No supported Python implementation in PYTHON_SINGLE_TARGET."

jan@funtoo ~ $ emerge -pqv '=dev-libs/gobject-introspection-1.34.2-r1'
[ebuild U ] dev-libs/gobject-introspection-1.34.2-r1 [1.32.1] USE="-doctool {-test} (-doc%)" PYTHON_SINGLE_TARGET="python2_7%" PYTHON_TARGETS="python2_7%"