code: def __getitem__(
      self, idx
  ) -> Tuple[
      np.ndarray, Optional[np.ndarray], Optional[np.ndarray], np.ndarray
  ]:
      return self.ds[idx]
  
imports: from typing import Optional, Sequence, Tuple, Union
  import numpy
  from darts import TimeSeries
  from .shifted_dataset import GenericShiftedDataset
  from .training_dataset import DualCovariatesTrainingDataset, FutureCovariatesTrainingDataset, MixedCovariatesTrainingDataset, PastCovariatesTrainingDataset, SplitCovariatesTrainingDataset
  from .utils import CovariateType
label_desc: Use image node_id 3 for calling the PastCovariatesSequentialDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: self