/* The *real* layout of a type object when allocated on the heap */
typedef struct _heaptypeobject {
	/* Note: there's a dependency on the order of these members
	   in slotptr() in typeobject.c . */
	PyTypeObject ht_type;
	PyNumberMethods as_number;
	PyMappingMethods as_mapping;
	PySequenceMethods as_sequence; /* as_sequence comes after as_mapping,
					  so that the mapping wins when both
					  the mapping and the sequence define
					  a given operator (e.g. __getitem__).
					  see add_operators() in typeobject.c . */
	PyBufferProcs as_buffer;
	PyObject *ht_name, *ht_slots;
	/* here are optional user slots, followed by the members. */
} PyHeapTypeObject;

/* Table mapping __foo__ names to tp_foo offsets and slot_tp_foo wrapper
   functions.  The offsets here are relative to the 'PyHeapTypeObject'
   structure, which incorporates the additional structures used for numbers,
   sequences and mappings.
   Note that multiple names may map to the same slot (e.g. __eq__,
   __ne__ etc. all map to tp_richcompare) and one name may map to multiple
   slots (e.g. __str__ affects tp_str as well as tp_repr). The table is
   terminated with an all-zero entry.  (This table is further initialized and
   sorted in init_slotdefs() below.) */

struct wrapperbase {
	char *name;
	int offset;
	void *function;
	wrapperfunc wrapper;
	char *doc;
	int flags;
	PyObject *name_strobj;
};

#define PyDescr_COMMON \
	PyObject_HEAD \
	PyTypeObject *d_type; \
	PyObject *d_name

typedef struct {
	PyDescr_COMMON;
	struct wrapperbase *d_base;
	void *d_wrapped; /* This can be any function pointer */
} PyWrapperDescrObject;


static PyDescrObject *
descr_new(PyTypeObject *descrtype, PyTypeObject *type, const char *name)
{
	PyDescrObject *descr;

	descr = (PyDescrObject *)PyType_GenericAlloc(descrtype, 0);
	if (descr != NULL) {
		Py_XINCREF(type);
		descr->d_type = type;
		descr->d_name = PyString_InternFromString(name);
		if (descr->d_name == NULL) {
			Py_DECREF(descr);
			descr = NULL;
		}
	}
	return descr;
}

PyObject *
PyDescr_NewWrapper(PyTypeObject *type, struct wrapperbase *base, void *wrapped)
{
	PyWrapperDescrObject *descr;

	descr = (PyWrapperDescrObject *)descr_new(&PyWrapperDescr_Type,
						 type, base->name);
	if (descr != NULL) {
		descr->d_base = base;
		descr->d_wrapped = wrapped;
	}
	return (PyObject *)descr;
}

/* This function is called by PyType_Ready() to populate the type's
   dictionary with method descriptors for function slots.  For each
   function slot (like tp_repr) that's defined in the type, one or more
   corresponding descriptors are added in the type's tp_dict dictionary
   under the appropriate name (like __repr__).  Some function slots
   cause more than one descriptor to be added (for example, the nb_add
   slot adds both __add__ and __radd__ descriptors) and some function
   slots compete for the same descriptor (for example both sq_item and
   mp_subscript generate a __getitem__ descriptor).

   In the latter case, the first slotdef entry encoutered wins.  Since
   slotdef entries are sorted by the offset of the slot in the
   PyHeapTypeObject, this gives us some control over disambiguating
   between competing slots: the members of PyHeapTypeObject are listed
   from most general to least general, so the most general slot is
   preferred.  In particular, because as_mapping comes before as_sequence,
   for a type that defines both mp_subscript and sq_item, mp_subscript
   wins.

   This only adds new descriptors and doesn't overwrite entries in
   tp_dict that were previously defined.  The descriptors contain a
   reference to the C function they must call, so that it's safe if they
   are copied into a subtype's __dict__ and the subtype has a different
   C function in its slot -- calling the method defined by the
   descriptor will call the C function that was used to create it,
   rather than the C function present in the slot when it is called.
   (This is important because a subtype may have a C function in the
   slot that calls the method from the dictionary, and we want to avoid
   infinite recursion here.) */

static int
add_operators(PyTypeObject *type)
{
	PyObject *dict = type->tp_dict;
	slotdef *p;
	PyObject *descr;
	void **ptr;

	init_slotdefs();
	for (p = slotdefs; p->name; p++) {
		if (p->wrapper == NULL)
			continue;
		ptr = slotptr(type, p->offset);
		if (!ptr || !*ptr)
			continue;
		if (PyDict_GetItem(dict, p->name_strobj))
			continue;
		descr = PyDescr_NewWrapper(type, p, *ptr);
		if (descr == NULL)
			return -1;
		if (PyDict_SetItem(dict, p->name_strobj, descr) < 0)
			return -1;
		Py_DECREF(descr);
	}
	if (type->tp_new != NULL) {
		if (add_tp_new_wrapper(type) < 0)
			return -1;
	}
	return 0;
}

case BUILD_CLASS:
			u = TOP();  // class 的动态信息
			v = SECOND();   // 基类 tuple
			w = THIRD();    // 类名
			STACKADJ(-2);
			x = build_class(u, v, w);
			SET_TOP(x);
			Py_DECREF(u);
			Py_DECREF(v);
			Py_DECREF(w);
			break;

static PyObject *
build_class(PyObject *methods, PyObject *bases, PyObject *name)
{
    // 1. find metaclass
    // 2. build class by metaclass: PyObject_CallFunctionObjArgs

	PyObject *metaclass = NULL, *result, *base;

	if (PyDict_Check(methods))
		metaclass = PyDict_GetItemString(methods, "__metaclass__");
	if (metaclass != NULL)
		Py_INCREF(metaclass);
	else if (PyTuple_Check(bases) && PyTuple_GET_SIZE(bases) > 0) {
		base = PyTuple_GET_ITEM(bases, 0);
		metaclass = PyObject_GetAttrString(base, "__class__");
		if (metaclass == NULL) {
			PyErr_Clear();
			metaclass = (PyObject *)base->ob_type;
			Py_INCREF(metaclass);
		}
	}
	else {
		PyObject *g = PyEval_GetGlobals();
		if (g != NULL && PyDict_Check(g))
			metaclass = PyDict_GetItemString(g, "__metaclass__");
		if (metaclass == NULL)
			metaclass = (PyObject *) &PyClass_Type;
		Py_INCREF(metaclass);
	}
	result = PyObject_CallFunctionObjArgs(metaclass, name, bases, methods, NULL);
	Py_DECREF(metaclass);
	if (result == NULL && PyErr_ExceptionMatches(PyExc_TypeError)) {
		/* A type error here likely means that the user passed
		   in a base that was not a class (such the random module
		   instead of the random.random type).  Help them out with
		   by augmenting the error message with more information.*/

		PyObject *ptype, *pvalue, *ptraceback;

		PyErr_Fetch(&ptype, &pvalue, &ptraceback);
		if (PyString_Check(pvalue)) {
			PyObject *newmsg;
			newmsg = PyString_FromFormat(
				"Error when calling the metaclass bases\n    %s",
				PyString_AS_STRING(pvalue));
			if (newmsg != NULL) {
				Py_DECREF(pvalue);
				pvalue = newmsg;
			}
		}
		PyErr_Restore(ptype, pvalue, ptraceback);
	}
	return result;
}