I think, the original docs *is* pretty intuitive. It says "Duplicate the file descriptor fd and build a socket object".  No one will think that the this method will close the original fd. Person using this method might of course, explicitly close the original fd in some other part of the code (as he may use it after creating the socket object too).

If at all anything is required, a line may be "The original file descriptor is unaffected", but again that seems redundant to me.