code: def __len__(self):
      return self.len
  
imports: from tqdm import tqdm
  from typing import Tuple
  from random import shuffle
  import pickle
  import random
  import numpy
  from pathlib import Path
  from pytorch_pretrained_bert.tokenization import BertTokenizer
label_desc: Use image node_id 2 for calling the QueryInstanceDataset obj's underlying member method code with example usage: obj.__len__() and returns: self