numexpr

numexpr looks like a very handy package to optimize performance on numpy array expressions. it basically breaks arrays into cache-friendly chunks, without needing python-level iterations. the 'vector virtual machine' runs in c, so it claims to have comparable speed to the scipy.weave.blitz expression compiler. and no extra c/c++-compiling step!

pytables comes with it, and with tables 2.2beta1 you can use the expressions on earray, etc (disk-based homogeneous arrays), so i think it should work with mmap.