code: def __len__(self) -> int:
      return self.imgs.shape[0]
  
imports: import pickle
  from contextlib import nullcontext
  from functools import partial
  import pytest
  import torch
  from torch.nn import Module
  from torch.utils.data import Dataset
  from torchmetrics.image.fid import FrechetInceptionDistance, NoTrainInceptionV3
  from torchmetrics.utilities.imports import _TORCH_FIDELITY_AVAILABLE
label_desc: Use image node_id 3 for calling the _ImgDataset obj's underlying member method code with example usage: obj.__len__() and returns: self