I told Gentoo to update my system today, thinking I'd see if the KDE compilation failures had been fixed. I missed Python 2.4.1 in the list of dependencies to be built (there were dozens and dozens of them). So, though the KDE compile still failed, Gentoo had already updated Python to 2.4.1, which broke pretty much everything.

The problem is that the Python packages are not registered as depending on a given Python version (indeed, they are generally compatible with both versions), but their installed versions are dependent on the Python version. That is, the packages are installed in /usr/lib/python23, and Python 2.4 does not look there (and wouldn't be able to use the binaries there if it did).

PyGame install failed due to not yet having Numpy installed on Python 2.4 (dependency didn't catch it because it is installed in 2.3). Oops. Looks like there's a lot of other packages breaking in there... hmm. That's not ideal. Oh well, price I pay for not paying attention when emerging I guess.