This facility didn't previously exist on any OS, so we had to make some innovations in terms of how Python lets modules build and load. In particular the Makefile used by Python previously hard-coded certain compiler flags etc. We had to make this dynamic. Also, we had to make some modifications to where Python looks for .so files when loading modules. Previously it would just assume that, say, /usr/lib/python2.4/foo.so was of the correct word size. Now, if it's running 64-bit, it will look for /usr/lib/python2.4/64/foo.so.
Similarly, building a Python module using the 64-bit Python will automagically install the .so file in the right place. Thanks to their architecture-independence, we don't need the same tricks for the .pyc files.
The need for this arose from the continuing work on Solaris dom0's running under Xen. The kernel/hypervisor interfaces provided are not 64-bit clean in the sense that 32-bit tools cannot deal with 64-bit domains; as a result, we need to run (the Python-based) xend as a native binary.
As an added bonus, Laca has also upgraded to Python 2.4.4, which finally enables the curses module on Solaris; also fixed are some niggling problems with accidental regeneration of .pyc files.