I see your point about the server_close purpose and I changed the patch to simulate the behavior of closed file (raising ValueError when operating on closed file).
I don't think that this should be an enhancement as what i try to do is return the behavior as it was before the change to the selectors module. When closing the socket using server_close at the next serve_forever loop you would have gotten ValueError for bad file descriptor to select. In the current implementation we actually keep on pulling on a already free resource.
I know that the user should call shutdown before the server_close but i think that as you said the behavior should simulate closed file. When someone will try to use any other function of a closed file he will receive a ValueError.