code: def _read_widget(self):
          
          getter = self._wid_info[self._wid][0]
          return getter(self._wid)
docs: 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.