def _decode(self, s):
        '''This converts from the external coding system (as passed to
        the constructor) to the internal one (unicode). '''
        if self.decoder is not None:
            return self.decoder.decode(s)
        else:
            raise TypeError("This screen was constructed with encoding=None, "
                            "so it does not handle bytes.")
This converts from the external coding system (as passed to
        the constructor) to the internal one (unicode).