Fix error handling, crete strong refs for interpolation

Author: johnslavik

Objects/exceptions.c

@@ -2706,23 +2706,29 @@ static PyObject *
 AttributeError_str(PyObject *op)
 {
     PyAttributeErrorObject *self = PyAttributeErrorObject_CAST(op);
-    PyObject *ret = NULL, *arg;
+    PyObject *arg, *obj = NULL, *name;
+
     Py_BEGIN_CRITICAL_SECTION(self);
-    if (
-        self->obj && self->name && PyUnicode_Check(self->name)
+    if (self->obj && self->name && PyUnicode_Check(self->name)
         && ((PyTuple_GET_SIZE(self->args) == 1
              && PyUnicode_Check(arg = PyTuple_GET_ITEM(self->args, 0))
              && PyUnicode_Equal(arg, self->name))
-            || PyTuple_GET_SIZE(self->args) == 0)
-    ) {
-        ret = PyUnicode_FromFormat("%R has no attribute '%U'",
-                                   self->obj, self->name);
+            || PyTuple_GET_SIZE(self->args) == 0))
+    {
+        obj = Py_NewRef(self->obj);
+        name = Py_NewRef(self->name);
     }
     Py_END_CRITICAL_SECTION();
-    if (!ret) {
-        ret = BaseException_str(op);
+
+    if (!obj) {
+        return BaseException_str(op);
     }
-    return ret;
+
+    PyObject *result = PyUnicode_FromFormat("%R has no attribute '%U'",
+                                            obj, name);
+    Py_DECREF(obj);
+    Py_DECREF(name);
+    return result;
 }
 
 static int