code: def __len__(self):
      return len(self.files)
  
imports: from copy import deepcopy
  from dataclasses import dataclass, field
  from random import shuffle
  from typing import Generator, List
  from paiargparse import pai_dataclass, pai_meta
  from tfaip.data.pipeline.definitions import PipelineMode
  import numpy
  import h5py
  from calamari_ocr.ocr.dataset.datareader.base import CalamariDataGenerator, InputSample, SampleMeta, CalamariDataGeneratorParams
  from calamari_ocr.utils import split_all_ext, glob_all
label_desc: Use image node_id 1 for calling the Hdf5 obj's underlying member method code with example usage: obj.__len__() and returns: len