code: def check_cursor_location(self):
          
          # Check whether cursor data position has changed relative
          # to previous value
          data_x, data_y = self.get_data_xy(self.last_win_x,
                                            self.last_win_y)
          if (data_x != self.last_data_x or
              data_y != self.last_data_y):
              self.last_data_x, self.last_data_y = data_x, data_y
              self.logger.debug("cursor location changed %.4f,%.4f => %.4f,%.4f" % (
                  self.last_data_x, self.last_data_y, data_x, data_y))
  
              # we make this call compatible with the motion callback
              # for now, but there is no concept of a button here
              button = 0
  
              self.make_ui_callback('cursor-changed', button, data_x, data_y)
  
          return data_x, data_y
docs: Check whether the data location of the last known position
          of the cursor has changed.  If so, issue a callback.