There's a wealth of numerical code in C++. Calling into C is pretty straightforward, but with C++ it's a complicated choice between Swig, sip, shiboken, BoostPython, ..., or hand-writing your language bindings to C++ code in extern "C".

I'd like it if it also made it easy to tap into C++. It's probably a very complicated problem, which is why it's unsolved.