New private API function _PyInstance_Lookup. gc will use this to figure

out whether __del__ exists, without executing any Python-level code.

Include/classobject.h

@@ -51,6 +51,18 @@ PyAPI_FUNC(PyObject *) PyMethod_Function(PyObject *);
 PyAPI_FUNC(PyObject *) PyMethod_Self(PyObject *);
 PyAPI_FUNC(PyObject *) PyMethod_Class(PyObject *);
 
+/* Look up attribute with name (a string) on instance object pinst, using
+ * only the instance and base class dicts.  If a descriptor is found in
+ * a class dict, the descriptor is returned without calling it.
+ * Returns NULL if nothing found, else a borrowed reference to the
+ * value associated with name in the dict in which name was found.
+ * The point of this routine is that it never calls arbitrary Python
+ * code, so is always "safe":  all it does is dict lookups.  The function
+ * can't fail, never sets an exceptionm, and NULL is not an error (it just
+ * means "not found").
+ */
+PyAPI_FUNC(PyObject *)_PyInstance_Lookup(PyObject *pinst, PyObject *name);
+
 /* Macros for direct access to these values. Type checks are *not*
    done, so use with care. */
 #define PyMethod_GET_FUNCTION(meth) \