code: def __len__(self):
      return self.length
  
file_path: accelerate/src/accelerate/test_utils/training.py
imports: import numpy
  import torch
  from torch.utils.data import DataLoader
  from accelerate.utils.dataclasses import DistributedType
label_desc: Use image node_id 2 for calling the RegressionDataset obj's underlying member method code with example usage: obj.__len__() and returns: self