code: def __len__(self):
      return len(self.img_list)
  
file_path: deep-learning-for-image-processing/pytorch_segmentation/unet/my_dataset.py
imports: import os
  from PIL import Image
  import numpy
  from torch.utils.data import Dataset
label_desc: Use image node_id 3 for calling the DriveDataset obj's underlying member method code with example usage: obj.__len__() and returns: len