Cross-Platform ReadKey

[Dustan]

I found this site that has the code for readkey for Windows, Unix, and
in an updated version, Mac:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/134892 .  The
Mac object returns a character whether or not a key was pressed.  I
modified the Windows object to do the same when I downloaded it, but I
have no idea how to make the Unix object instantly return either the
character or an empty string. Any help???