In the following scenario, the object is not meant to be instantiated within Python (hence no tp_new or tp_init). Calling the ThingType as a function using PyObject_CallObject results in a segfault in _PyObject_FastCallDict, I believe because there are no constructors.
After creating the object using CreatePythonThing, the function get_height is not set unless a workaround is applied - to call dir(thing), which as a side effect initializes the object's properties. The workaround is already present in CreatePythonThing.
#include <Python.h>
typedef struct {
PyObject_HEAD
/* Type-specific fields go here. */
Eval *eval;
} Thing;
static PyObject* ThingGetHeight(PyObject* self, PyObject* args)
{
return PyLong_FromLong(1);
}
static PyMethodDef ThingMethods[] = {
{"get_height", ThingGetHeight, METH_NOARGS, "Get thing height"},
{NULL, NULL, 0, NULL} /* Sentinel */
};
static PyTypeObject ThingType = {
PyVarObject_HEAD_INIT(NULL, 0)
"thing.Thing", /* tp_name */
sizeof(Thing), /* tp_basicsize */
0, /* tp_itemsize */
0, /* tp_dealloc */
0, /* tp_print */
0, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_reserved */
0, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
0, /* tp_hash */
0, /* tp_call */
0, /* tp_str */
0, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT, /* tp_flags */
"Thing", /* tp_doc */
0, 0, 0, 0, 0, 0,
ThingMethods, /* tp_methods */
};
Thing* CreatePythonThing(Eval *eval)
{
Thing* obj = PyObject_New(Thing, &ThingType);
obj->eval = eval;
obj = (Thing*) PyObject_Init((PyObject*) obj, &ThingType);
// I don't understand why, but the above does not fully initialize the object. The method
// table is not set. Calling `dir` on the object causes it to be initialized, so this is
// a workaround.
PyObject_Dir((PyObject*) obj);
return obj;
}
