Say I have my object layout defined as:
typedef struct {
PyObject_HEAD
// Other stuff...
} pyfoo;
...and my type definition:
<Call PyObject_New(), followed by PyObject_Init().
EDIT: The best way is to call the class object, just like in Python itself:
/* Pass two arguments, a string and an int. */
PyObject *argList = Py_BuildValue("si", "hello", 42);
/* Call the class object. */
PyObject *obj = PyObject_CallObject((PyObject *) &pyfoo_T, argList);
/* Release the argument list. */
Py_DECREF(argList);