If libuv closes the FD (step 3), won’t you get the same sort of problem if the uvloop user tries to do something else with the Python socket object, e.g. call getpeername()?

I see the fileno=... parameter for sockets as a parallel to the os.fdopen() function, which does raise exceptions from FileIO.close().

Maybe one option is to only trigger a DeprecationWarning, and raise a proper OSError in a future version.