code: def __len__(self):
      return len(self.df)
  
file_path: BigDL/python/orca/example/learn/pytorch/brainMRI/dataset.py
imports: import numpy
  import random
  import cv2
  import torch
  import torchvision.transforms
  import torch.utils.data
label_desc: Use image node_id 2 for calling the BrainDataset obj's underlying member method code with example usage: obj.__len__() and returns: len