I'm trying to build numpy with python27, 64-bit, on OSX 10.5.8. 

When I run  python setup.py build,   only 32-bit binaries get built.   I can see what is happening is that not 64-bit flags are getting passed to the c compiler (I don't know about the fortran compiler.

So I have two questions;

1) Shouldn't the system be determining that 64-bit nature automatically?   I've used the same build process on the same machine (in what I thought were identical situations, apparently not) a number of times in the past, and it has always built correctly as 64 bit.   I never needed to set compiler options. 

2) How do I set  C compiler options for the numpy build process?