Backport to 2.2.x:

Address the residual issue with the fix for SF 551412 in
_PyType_Lookup().  Decided to clear the error condition in the
unfortunate but unlikely case that PyType_Ready() fails.

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index f5a1a01a49af6b6cd106c710d319e530b6611764..c2264541cec895e0baf5c386bcc156d1c7e49e12 100644 (file)
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -1219,8 +1219,18 @@ _PyType_Lookup(PyTypeObject *type, PyObject *name)
        /* Look in tp_dict of types in MRO */
        mro = type->tp_mro;
        if (mro == NULL) {
-               if (PyType_Ready(type) < 0)
+               if (PyType_Ready(type) < 0) {
+                       /* It's not ideal to clear the error condition,
+                          but this function is documented as not setting
+                          an exception, and I don't want to change that.
+                          When PyType_Ready() can't proceed, it won't
+                          set the "ready" flag, so future attempts to ready
+                          the same type will call it again -- hopefully
+                          in a context that propagates the exception out.
+                       */
+                       PyErr_Clear();
                        return NULL;
+               }
                mro = type->tp_mro;
                assert(mro != NULL);
        }