gh-96663: Add a better error message for __dict__-less classes setattr (#103232)

1 files changed, 13 insertions, 3 deletions

diff --git a/Objects/object.c b/Objects/object.c
index d30e048..bfbc871 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -1576,9 +1576,18 @@ _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
         }
         if (dictptr == NULL) {
             if (descr == NULL) {
-                PyErr_Format(PyExc_AttributeError,
-                            "'%.100s' object has no attribute '%U'",
-                            tp->tp_name, name);
+                if (tp->tp_setattro == PyObject_GenericSetAttr) {
+                    PyErr_Format(PyExc_AttributeError,
+                                "'%.100s' object has no attribute '%U' and no "
+                                "__dict__ for setting new attributes",
+                                tp->tp_name, name);
+                }
+                else {
+                    PyErr_Format(PyExc_AttributeError,
+                                "'%.100s' object has no attribute '%U'",
+                                tp->tp_name, name);
+                }
+                set_attribute_error_context(obj, name);
             }
             else {
                 PyErr_Format(PyExc_AttributeError,
@@ -1611,6 +1620,7 @@ _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
                          "'%.100s' object has no attribute '%U'",
                          tp->tp_name, name);
         }
+        set_attribute_error_context(obj, name);
     }
   done:
     Py_XDECREF(descr);