Callback via a function pointer (1)

gridloop1_C calls a function like

double somefunc(double x, double y)

but our function is a Python object...

Trick: store the Python function in

PyObject* _pyfunc_ptr;  /* global variable */

and make a ``wrapper'' for the call:

double _pycall(double x, double y)
{
  /* perform call to Python function object in _pyfunc_ptr */
}