code: def on_scroll(self, event):
      print(event.button, event.step)
      increment = 1 if event.button == "up" else -1
      max_index = self.X.shape[-1] - 1
      self.index = np.clip(self.index + increment, 0, max_index)
      self.update()
  
imports: import matplotlib.pyplot
  import numpy
label_desc: Use image node_id 2 for calling the IndexTracker obj's underlying member method code with example usage: obj.on_scroll(event) without return types