Return string representation of the device, including
        the connection state

def describe_connection(self):
        """Return string representation of the device, including
        the connection state"""
        if self.device==None:
            return "%s [disconnected]" % (self.name)
        else:
            return "%s connected to %s %s version: %s [serial: %s]" % (self.name, 
                self.vendor_name, self.product_name,
                self.version_number, self.serial_number)