The Apache server interfaces with the Python interpreter via a callback object obCallBack. When a subinterpreter is created, an instance of obCallBack is created in this subinterpreter. Interestingly, obCallBack is not written in C, it is written in Python and the code for it is in the apache module. Mod_python only uses the C API to import apache and then instantiate obCallBack, storing a reference to the instance in the interpreter dictionary described above. Thus, the values in the interpreter dictionary are callback object instances.
When a request handler is invoked by Apache, mod_python uses the obCallBack reference to call its method Dispatch, passing it the name of the handler being invoked as a string.
The Dispatch method then does the rest of the work of importing the user module, resolving the callable object in it and calling it passing it a request object.