code: def _set_mode(self, mode):
          '''
          Sets call_transform_mode to point to the
          center_transform or corner_transform
          '''
          if mode == CENTER:
              self._call_transform_mode = self._center_transform
          elif mode == CORNER:
              self._call_transform_mode = self._corner_transform
          else:
              raise ValueError('mode must be CENTER or CORNER'f _set_mode(self, mode):
          '''
          Sets call_transform_mode to point to the
          center_transform or corner_transform
          '''
          if mode == CENTER:
              self._call_transform_mode = self._center_transform
          elif mode == CORNER:
              self._call_transform_mode = self._corner_transform
          else:
              raise ValueError('mode must be CENTER or CORNER')
docs: Sets call_transform_mode to point to the
          center_transform or corner_transform