The solution suggested by klimkin seems to have made it into revision 35513 as a fix to bug #887279.

I'm not sure that this is necessarily the right solution to this bug or #887279, as a socket disconnect isn't necessarily an error condition, otherwise .handle_close_event() shouldn't exist for select-based loops, and it should always be an error.

Suggest switching to the last if clause of readwrite() to...

if flags & (select.POLLERR | select.POLLNVAL):
    obj.handle_expt_event()
if flags & select.POLLHUP:
    obj.handle_close_event()