code: def register_callback(self, callback, remove=False):
          
  
          # (Un)Register the callback.
          if remove and callback in self.callbacks:
              self.callbacks.remove(callback)
          elif not remove and callback not in self.callbacks:
              self.callbacks.append(callback)
docs: (Un)Register a callback
  
          Parameters
          ----------
          callback: method handle
              Method to be registered or unregistered.
          remove=False: bool
              Whether to unregister the callback.