Registering module functions

The method table must always be present - it lists the functions that should be callable from Python:

static PyMethodDef ext_gridloop_methods[] = {
  {"gridloop1",    /* name of func when called from Python */
   gridloop1,      /* corresponding C function */
   METH_VARARGS,   /* ordinary (not keyword) arguments */
   gridloop1_doc}, /* doc string for gridloop1 function */
  {"gridloop2",    /* name of func when called from Python */
   gridloop2,      /* corresponding C function */
   METH_VARARGS,   /* ordinary (not keyword) arguments */
   gridloop2_doc}, /* doc string for gridloop1 function */
  {NULL, NULL}
};

METH_KEYWORDS (instead of METH_VARARGS) implies that the function takes 3 arguments (self, args, kw)