def prepare_data(self) -> None:
        """
        Used by pytorch_lighting

        Loads training data to self.train_dataset
        Loads validation data to self.val_dataset
        """
        (self.train_dataset, self.val_dataset,) = ArithmeticDataset.splits(
            train_pct=self.hparams.train_data_pct,  # type: ignore
            operator=self.hparams.math_operator,  # type: ignore
            operand_length=self.hparams.operand_length,  # type: ignore
            data_dir=self.hparams.datadir,  # type: ignore
        )

        Used by pytorch_lighting

        Loads training data to self.train_dataset
        Loads validation data to self.val_dataset
        
grok/training.py