Version 2.1 (...)
PyObjC can now run in 64-bit mode.
NOTE: 64-bit support is beta quality, that is: all unittests pass, but I haven't tried running real programs yet and hence there might be issues lurking below the surface.
NOTE2: PPC64 support is completely untested, aka "it compiles and therefore must work".
This requires Leopard (OSX 10.5), earlier version of the OS don't have a 64-bit Objective-C runtime at all. This currently also requires a copy of python that was build with MACOSX_DEPLOYMENT_TARGET=10.5.
Note that class posing (the poseAsClass_ class method) is not supported in 64-bit mode. It is also not possible to create new protocols in 64-bit code. Neither are supported by the 64-bit runtime APIs (that is, it is a restriction in Apple's Objective-C 2.0 runtime).