Returns the value currently stored into the widget, after
        transforming it accordingly to possibly specified function.

        This is implemented by calling the getter provided by the
        user. This method can raise InvalidValue (raised by the
        getter) when the value in the widget must not be considered as
        valid.

def _read_widget(self):
        """Returns the value currently stored into the widget, after
        transforming it accordingly to possibly specified function.

        This is implemented by calling the getter provided by the
        user. This method can raise InvalidValue (raised by the
        getter) when the value in the widget must not be considered as
        valid."""
        getter = self._wid_info[self._wid][0]
        return getter(self._wid)