Proxy super().x = y and del super().x

This patch was originally contributed by Daniel Urban, whose summary follows: > I'm attaching a patch implementing super.__setattr__ (and > __delattr__). > The implementation in the patch only works, if super can find a data > descriptor in the MRO, otherwise it throws an AttributeError. As it > can be seen in the tests, in some cases this may result in > counter-intuitive behaviour. But I wasn't able to find another > behaviour, that is consistent with both super.__getattr__ and normal > __setattr__ semantics. Co-authored-by: hab <_@habnab.it> Co-authored-by: Markus Kitsinger (SwooshyCueb) <root@swooshalicio.us>
SwooshyCueb · Jun 4, 2012 · Oct 22, 2026 · Dec 7, 2021 · b955e79d6f0b777de9a2b69b452b64d9f4f3e6f5 · JelleZijlstra
commit b955e79d6f0b777de9a2b69b452b64d9f4f3e6f5
diff --git a/Lib/test/test_super.py b/Lib/test/test_super.py
@@ -39,6 +39,26 @@ class F(E):
 class G(A):
     pass
 
+class P:
+    @property
+    def x(self):
+        return self._x
+    @x.setter
+    def x(self, value):
+        self._x = value
+    @x.deleter
+    def x(self):
+        del self._x
+
+class Q(P):
+    pass
+
+class R(P):
+    x = None
+
+class S(Q, R):
+    pass
+
 
 class TestSuper(unittest.TestCase):
 
@@ -317,6 +337,60 @@ def test_super_init_leaks(self):
         for i in range(1000):
             super.__init__(sp, int, i)
 
+    def test_super_setattr(self):
+        # See issue14965
+        val = object()
+        p = P()
+        with self.assertRaises(AttributeError):
+            super(P, p).x = val
+        with self.assertRaises(AttributeError):
+            del super(P, p).x
+
+        q = Q()
+        super(Q, q).x = val
+        self.assertIs(q.__dict__['_x'], val)
+        self.assertIs(super(Q, q).x, val)
+        del super(Q, q).x
+        self.assertNotIn('_x', q.__dict__)
+
+        r = R()
+        super(R, r).x = val
+        self.assertIs(r.__dict__['_x'], val)
+        self.assertIs(super(R, r).x, val)
+        del super(R, r).x
+        self.assertNotIn('_x', r.__dict__)
+
+        s = S()
+        with self.assertRaises(AttributeError):
+            super(S, s).x = val
+        with self.assertRaises(AttributeError):
+            del super(S, s).x
+        self.assertIs(super(S, s).x, None)
+
+    def test_super_property(self):
+        # See issue14965
+        class T(P):
+            def __init__(self, x):
+                self.x = x
+            @property
+            def x(self):
+                return super().x / 2
+            @x.setter
+            def x(self, value):
+                super().x = value * 2
+            @x.deleter
+            def x(self):
+                del super().x
+        t = T(1)
+        self.assertEqual(t.x, 1)
+        self.assertEqual(t._x, 2)
+        t.x = 10
+        self.assertEqual(t.x, 10)
+        self.assertEqual(t._x, 20)
+        del t.x
+        self.assertFalse(hasattr(t, 'x'))
+        self.assertFalse(hasattr(t, '_x'))
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-12-06-22-56-19.bpo-14965.CcMLxs.rst b/Misc/NEWS.d/next/Core and Builtins/2021-12-06-22-56-19.bpo-14965.CcMLxs.rst
@@ -0,0 +1,3 @@
+Proxying data descriptor setters with ``super().x = y`` and deleters with ``del
+super().x`` will now follow getter use with ``super().x``. Previously, these
+would unconditionally fail. Patch by Daniel Urban.
@@ -8831,6 +8831,71 @@ super_getattro(PyObject *self, PyObject *name)
     return PyObject_GenericGetAttr(self, name);
 }
 
+static int
+super_setattro(PyObject *self, PyObject *name, PyObject *value)
+{
+    superobject *su = (superobject *)self;
+    int skip = (su->obj_type == NULL);
+
+    if (!skip) {
+        /* We don't allow overwriting __class__. */
+        skip = (PyUnicode_Check(name) &&
+            PyUnicode_GET_LENGTH(name) == 9 &&
+            PyUnicode_CompareWithASCIIString(name, "__class__") == 0);
+    }
+
+    if (!skip) {
+        PyObject *mro, *descr, *tmp, *dict;
+        PyTypeObject *starttype;
+        descrsetfunc f;
+        Py_ssize_t i, n;
+        int done = 0, result = 0;
+
+        starttype = su->obj_type;
+        mro = starttype->tp_mro;
+
+        if (mro == NULL)
+            n = 0;
+        else {
+            assert(PyTuple_Check(mro));
+            n = PyTuple_GET_SIZE(mro);
+        }
+        for (i = 0; i < n; i++) {
+            if ((PyObject *)(su->type) == PyTuple_GET_ITEM(mro, i))
+                break;
+        }
+        i++;
+        descr = NULL;
+        /* keep a strong reference to mro because starttype->tp_mro can be
+           replaced during PyDict_GetItem(dict, name)  */
+        Py_INCREF(mro);
+        for (; i < n; i++) {
+            tmp = PyTuple_GET_ITEM(mro, i);
+            if (PyType_Check(tmp))
+                dict = ((PyTypeObject *)tmp)->tp_dict;
+            else
+                continue;
+            descr = PyDict_GetItem(dict, name);
+            if (descr != NULL) {
+                Py_INCREF(descr);
+                f = Py_TYPE(descr)->tp_descr_set;
+                if ((f != NULL) && PyDescr_IsData(descr)) {
+                    /* We found a data descriptor: */
+                    result = f(descr, su->obj, value);
+                    done = 1;
+                }
+                Py_DECREF(descr);
+                break;
+            }
+        }
+        Py_DECREF(mro);
+        if (done) {
+            return result;
+        }
+    }
+    return PyObject_GenericSetAttr(self, name, value);
+}
+
 static PyTypeObject *
 supercheck(PyTypeObject *type, PyObject *obj)
 {
@@ -9082,7 +9147,7 @@ PyTypeObject PySuper_Type = {
     0,                                          /* tp_call */
     0,                                          /* tp_str */
     super_getattro,                             /* tp_getattro */
-    0,                                          /* tp_setattro */
+    super_setattro,                             /* tp_setattro */
     0,                                          /* tp_as_buffer */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
         Py_TPFLAGS_BASETYPE,                    /* tp_flags */