def change_value(self):
        """Sort the values.

        If None is returned from the sort_sequence function,
        the widget isn't updated.
        """
        ### retrieve new values from the sort_list function

        output = sort_sequence(
            self.value,
            self.available_items,
        )

        ### if the output is not None, update the value
        ### and available items in the widget

        if output is not None:

            value = output
            self.set(value)
Sort the values.

        If None is returned from the sort_sequence function,
        the widget isn't updated.
        
nodezator/widget/sortingbutton.py