Writing up a test case, I noticed that it makes sense to let PyErr_SetExcInfo() steal the references. This matches the main use case of saving and restoring the fields. For the getter, it's still best to return new references in order to support the use case of just reading the fields, as well as the use case of reading and clearing the fields (which a subsequent call to PyErr_SetExcInfo(NULL,NULL,NULL) does).