docs: def pref_update(self, key, new_val):
          """ Changes a preference value and saves it to disk """
          print('Update and save pref from: %s=%r, to: %s=%r' %
                (key, six.text_type(self[key]), key, six.text_type(new_val)))
          self.__setattr__(key, new_val)
          return self.save()