> On Windows socket.fromfd() is not possible. Socket handlers and file
> descriptors are different types using different API methods. Other
> examples for the discrepancy are select.select() and select.poll(). On
> Windows they don't work on file.

I know, but, I was thinking of it taking the fileno() of some other
socket object as argument.

In any case I think the test should not be based on whether os.name ==
'nt' but on the presence of something in the _socket module.