A list of terms that are outputs of this pipeline.

        Includes all terms registered as data outputs of the pipeline, plus the
        screen, if present.

def _output_terms(self):
        """
        A list of terms that are outputs of this pipeline.

        Includes all terms registered as data outputs of the pipeline, plus the
        screen, if present.
        """
        terms = list(six.itervalues(self._columns))
        screen = self.screen
        if screen is not None:
            terms.append(screen)
        return terms