That's what tends to happen, at least in the code I've worked on. C/C++ for the bits that need to "talk" to the OS, python/perl/bash for scripting purposes, and

That's what tends to happen, at least in the code I've worked on. C/C++ for the bits that need to "talk" to the OS, python/perl/bash for scripting purposes, and Fortran for the number-crunching core.