def _scroll(self, step):
        """
        Scroll up/down dictated by 'step' the items
        and then display that item.

        Has no effect if the widget is disabled.
        """
        if self.error or not self.is_enabled:
            return
        self._line_index = (self._line_index + step) % len(self._lines)
        self.show_line()

        Scroll up/down dictated by 'step' the items
        and then display that item.

        Has no effect if the widget is disabled.
        
libqtile/widget/redshift.py