>=pycairo-1.10.0-r2, supporting multiple python targets, depends (conditionally) on xpyb, which only supports single-target mode. This is not allowed (cf. python-single-r1.eclass), and also makes little sense. Easiest solution: Remove the dep (in effect: revert bug #416565) Better solution: Make xpyb work with multiple python-versions. As it installs C-Header-Files, this might be a little bit more complicated.
Sync, this was fixed about a week ago with xpyb-1.3.1-r2.