Poll
        
        Check for a non-response string generated by LCDd and return any string read.
        LCDd generates strings for key presses, menu events & screen visibility changes.

def poll(self):
        """
        Poll
        
        Check for a non-response string generated by LCDd and return any string read.
        LCDd generates strings for key presses, menu events & screen visibility changes.
        """
        if select.select([self.tn], [], [], 0) == ([self.tn], [], []):
            response = urllib.unquote(self.tn.read_until(b"\n").decode())
            if self.debug: print "Telnet Poll: %s" % (response[:-1])
            # TODO Keep track of which screen is displayed
            return response
        else:
            return None