[C++-sig] Multiple modules in a file

Hi, I am quite new at extending python with c++. I am using the boost libraries on gnu/linux. I have many classes (with inheritance) that I would like to expose to python. Is there some way to have many python modules in one file? Like, core.so contains a string class and a memory class. I tried just compiling everything as a shared library and importing into python with "import core.string" but then I get the error "ImportError: dynamic module does not define init function (initcore)" Im not really sure what that means.