If you want to build certain old binaries on Xcode 4, for example Reportlab (a PDF conversion tool), you’ll likely run into some compilation issues.
Turns out PPC libraries are no longer in xcode 4. However, ARCHFLAGS is supported and you can tell gcc not to use ppc:
export ARCHFLAGS=’-arch i386 -arch x86_64’
This happens because Apple’s new Xcode removes the assembler for PPC, while the core system retains their PPC images in the fat binaries. Python compiles C extensions with the same compiler flags that Python itself was compiled with. It seems that that nobody at Apple took the time to install a Python C extensions on their Xcode 4-enabled systems…