code: def __len__(self) -> int:
      return self._length
  
imports: from typing import Tuple
  import numpy
  import pytest
  from tensorflow.keras.utils import Sequence
  import determined
  from determined import keras
  from determined.common import check
  from tests.experiment import tf_utils
label_desc: Use image node_id 2 for calling the IdentitySequence obj's underlying member method code with example usage: obj.__len__() and returns: self