code: def __len__(self):
      return len(self.base)
  
imports: from __future__ import print_function
  import argparse
  import multiprocessing
  import random
  import sys
  import numpy
  import chainer
  import chainer.cuda
  from chainer import training
  from chainer.training import extensions
  import chainermn
  import models.alex
  import models.googlenet
  import models.googlenetbn
  import models.nin
  import models.resnet50
label_desc: Use image node_id 2 for calling the PreprocessedDataset obj's underlying member method code with example usage: obj.__len__() and returns: len