code: def __len__(self):
      return len(self.reader)
  
imports: import io
  import logging
  from typing import Optional
  import torch
  import torch.utils.data
  from PIL import Image
  from .readers import create_reader
label_desc: Use image node_id 3 for calling the ImageDataset obj's underlying member method code with example usage: obj.__len__() and returns: len