getpeername() on stdin?

[random832 at fastmail.us]

On Thu, Oct 31, 2013, at 21:12, Nobody wrote:
> On Thu, 31 Oct 2013 12:16:23 -0400, Roy Smith wrote:
> 
> > I want to do getpeername() on stdin.  I know I can do this by wrapping a
> > socket object around stdin, with
> > 
> > s = socket.fromfd(sys.stdin.fileno(), family, type)
> > 
> > but that requires that I know what the family and type are.   What I want
> > to do is discover the family and type by looking at what getpeername()
> > and/or getsockname() return.  Can this be done with the standard library?
> 
> I think that you'd need to use ctypes to access the underlying
> getpeername() function from libc.

If it's possible to get this information with only the fd, then why does
socket.fromfd require them?