Sets or returns the option selected in a ButtonGroup by its text value.

def value_text(self):
        """
        Sets or returns the option selected in a ButtonGroup by its text value.
        """
        search = self._selected.get() # a string containing the selected option
        # This is a bit nasty - suggestions welcome
        for item in self._rbuttons:
            if item.value == search:
                return item.text
        return ""