Per A. Jesse Jiryu Davis:

===========================
# mod.py
class C(object):
    pass

class Pool(object):
    def __del__(self):
        print('del')
        list()

C.pool = Pool()
===========================

===========================

int main()
{
    Py_Initialize();
    PyThreadState *tstate_enter = PyThreadState_Get();
    PyThreadState *tstate = Py_NewInterpreter();

    PyRun_SimpleString("import mod\n");
    if (PyErr_Occurred()) {
        PyErr_Print();
    }
    Py_EndInterpreter(tstate);
    PyThreadState_Swap(tstate_enter);
    printf("about to finalize\n");
    Py_Finalize();
    printf("done\n");

    return 0;
}
===========================

See:
http://emptysqua.re/blog/a-normal-accident-in-python-and-mod-wsgi/
https://github.com/GrahamDumpleton/mod_wsgi/issues/43