getpeername() on stdin?

[Roy Smith]

In article <mailman.1937.1383332149.18130.python-list at python.org>,
 random832 at fastmail.us wrote:

> 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?

Because socket.fromfd() is a very simplistic alternate way to create a 
socket object, which meets a common use case that happens not to be my 
use case.