Repository: Project-MONAI/MONAI
File: monai/data/dataset.py (Python)

Code before:

        """
        self.data = data
        if self.cache_dir is not None and self.cache_dir.exists():
            shutil.rmtree(self.cache_dir, ignore_errors=True)
            self.cache_dir.mkdir(parents=True, exist_ok=True)

    def _pre_transform(self, item_transformed):
        """
        Process the data from original state up to the first random element.

        Args:
            item_transformed: The data to be transformed

        Returns:
            the transformed element up to the first identified
            random transform object

        """
        if not isinstance(self.transform, Compose):
            raise ValueError("transform must be an instance of monai.transforms.Compose.")

        first_random = self.transform.get_index_of_first(
            lambda t: isinstance(t, RandomizableTrait) or not isinstance(t, Transform)
        )

        item_transformed = self.transform(item_transformed, end=first_random, threading=True)

        if self.reset_ops_id:
            reset_ops_id(item_transformed)
        return item_transformed

    def _post_transform(self, item_transformed):
        """
        Process the data from before the first random transform to the final state ready for evaluation.

        Args:
            item_transformed: The data to be transformed (already processed up to the first random transform)

        Returns:
            the transformed element through the random transforms

        """
        if not isinstance(self.transform, Compose):
            raise ValueError("transform must be an instance of monai.transforms.Compose.")

        first_random = self.transform.get_index_of_first(
            lambda t: isinstance(t, RandomizableTrait) or not isinstance(t, Transform)
        )
        return self.transform(item_transformed, start=first_random)


Review comment (performance):
please make sure the PR can pass basic dataset tests:
```
python -m tests.test_cachedataset
python -m tests.test_persistentdatset
python -m tests.test_cachedataset_persistent_workers
```

Code after:
        self.transform_hash = transform_hash.decode("utf-8")

    def set_data(self, data: Sequence):
        """
        Set the input data and delete all the out-dated cache content.

        """
        self.data = data
        if self.cache_dir is not None and self.cache_dir.exists():
            shutil.rmtree(self.cache_dir, ignore_errors=True)
            self.cache_dir.mkdir(parents=True, exist_ok=True)

    def _pre_transform(self, item_transformed):
        """
        Process the data from original state up to the first random element.

        Args:
            item_transformed: The data to be transformed

        Returns:
            the transformed element up to the first identified
            random transform object

        """
        if not isinstance(self.transform, Compose):
            raise ValueError("transform must be an instance of monai.transforms.Compose.")

        first_random = self.transform.get_index_of_first(
            lambda t: isinstance(t, RandomizableTrait) or not isinstance(t, Transform)
        )

        item_transformed = self.transform(item_transformed, end=first_random, threading=True)

        if self.reset_ops_id:
            reset_ops_id(item_transformed)
        return item_transformed

    def _post_transform(self, item_transformed):
        """
        Process the data from before the first random transform to the final state ready for evaluation.

        Args:
            item_transformed: The data to be transformed (already processed up to the first random transform)

        Returns:
            the transformed element through the random transforms

        """
        if not isinstance(self.transform, Compose):
            raise ValueError("transform must be an instance of monai.transforms.Compose.")