code: def get_key(self, bucket_index):
      r"""
      A method that returns an encoded key that represents the current batch and
      bucket index.
      Args:
          bucket_index (int): index of the bucket being processed in backward
      """
      return f"{self.batch_number},{bucket_index}"
  
label_desc: Use image node_id 2 for calling the BasicHookState obj's underlying member method code with example usage: obj.get_key(bucket_index) and returns: self, str, bucket_index