- The extended type structure used for heap types (new-style

classes defined by Python code using a class statement) is now
  exported from object.h as PyHeapTypeObject.  (SF patch #696193.)

Include/object.h

@@ -327,6 +327,28 @@ typedef struct _typeobject {
 } PyTypeObject;
 
 
+/* 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 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 *name, *slots;
+	/* here are optional user slots, followed by the members. */
+} PyHeapTypeObject;
+
+/* access macro to the members which are floating "behind" the object */
+#define PyHeapType_GET_MEMBERS(etype) \
+    ((PyMemberDef *)(((char *)etype) + (etype)->type.ob_type->tp_basicsize))
+
+
 /* Generic type check */
 PyAPI_FUNC(int) PyType_IsSubtype(PyTypeObject *, PyTypeObject *);
 #define PyObject_TypeCheck(ob, tp) \