Refactor instancemethod_descr_get() to (a) be more clear, (b) be safe

in the light of weird args, and (c) not to expect None (which is now
changed to NULL by slot_tp_descr_get()).

diff --git a/Objects/classobject.c b/Objects/classobject.c
index bc2234528b801faa7f7ac3ca3feacbfc62be90ed..80aabbf6c2895bbf68a21225abb16d5e8a48acdd 100644 (file)
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -2414,19 +2414,29 @@ instancemethod_call(PyObject *func, PyObject *arg, PyObject *kw)
 }
 
 static PyObject *
-instancemethod_descr_get(PyObject *meth, PyObject *obj, PyObject *class)
+instancemethod_descr_get(PyObject *meth, PyObject *obj, PyObject *cls)
 {
        /* Don't rebind an already bound method, or an unbound method
-          of a class that's not a base class of class */
-       if (PyMethod_GET_SELF(meth) != NULL ||
-           (PyMethod_GET_CLASS(meth) != NULL &&
-            !PyObject_IsSubclass(class,  PyMethod_GET_CLASS(meth)))) {
+          of a class that's not a base class of cls. */
+
+       if (PyMethod_GET_SELF(meth) != NULL) {
+               /* Already bound */
                Py_INCREF(meth);
                return meth;
        }
-       if (obj == Py_None)
-               obj = NULL;
-       return PyMethod_New(PyMethod_GET_FUNCTION(meth), obj, class);
+       /* No, it is an unbound method */
+       if (PyMethod_GET_CLASS(meth) != NULL && cls != NULL) {
+               /* Do subclass test.  If it fails, return meth unchanged. */
+               int ok = PyObject_IsSubclass(cls, PyMethod_GET_CLASS(meth));
+               if (ok < 0)
+                       return NULL;
+               if (!ok) {
+                       Py_INCREF(meth);
+                       return meth;
+               }
+       }
+       /* Bind it to obj */
+       return PyMethod_New(PyMethod_GET_FUNCTION(meth), obj, cls);
 }
 
 PyTypeObject PyMethod_Type = {