I've just encountered problems (and solved) emerging net-zope/zope. This package is depending on the lib pyexpat in <python-root>/lib-dynload/. I'm guessing this lib will get build and installed if and only if the package dev-libs/expat is installed, because my python 2.4 had it, but 2.3 didn't. Since all ARCH zope ebuilds uses python 2.3, this fails.
There's no flag for this lib and remerging python 2.3 solved the problem. My guess is that either a flag or (complex) dependency solves this problem.
There's really nothing we could about this, I'm afraid...
Unfortunately we can't fix it atn. The only viable solution is to manualy install python packages with python2.3
*** This bug has been marked as a duplicate of 114376 ***