Error messages are already silenced if sys.stderr is None or closed.>>> sys.stderr.close()>>> 1/0>>> >>> sys.stderr = None>>> 1/0>>> I think that such things as _Errbox are application level solutions. report_callback_exception() is designed to be overwritten for this purpose. Application can decide to pop up message box always, not only when sys.stderr is None, or tracebacks to a log, or add application icon and scrollbar on message box, or output error on special area on main windows.Definitely it would be good to add something like _Errbox to IDLE. But this will be other issue. This issue is only about "crashing" of default implementation, and if my patch fixes it, I want to commit it and close the issue.