Add attribute to flag persistence in Dataset classes

RELEASE.md

@@ -19,6 +19,7 @@
 * Added `source_dir` explicitly in `pyproject.toml` for non-src layout project.
 * `MemoryDataset` entries are now included in free outputs.
 * Removed black dependency and replaced it functionality with `ruff format`.
+* Added the `_EPHEMERAL` attribute to `AbstractDataset` and other Dataset classes that inherit from it.
 
 ## Breaking changes to the API
 * Added logging about not using async mode in `SequentiallRunner` and `ParallelRunner`.

docs/source/data/how_to_create_a_custom_dataset.md

@@ -38,6 +38,8 @@
 `AbstractDataset` is generically typed with an input data type for saving data, and an output data type for loading data.
 This typing is optional however, and defaults to `Any` type.
 
+The `_EPHEMERAL` boolean attribute in `AbstractDataset` indicates if a dataset is persistent. For example, in the case of [MemoryDataset](/kedro.io.MemoryDataset), which is not persistent, it is set to True. By default, `_EPHEMERAL` is set to False.
+
 Here is an example skeleton for `ImageDataset`:
 
 <details>

kedro/io/cached_dataset.py

@@ -60,6 +60,8 @@ def __init__(
             ValueError: If the provided dataset is not a valid dict/YAML
                 representation of a dataset or an actual dataset.
         """
+        self._EPHEMERAL = True
+
         if isinstance(dataset, dict):
             self._dataset = self._from_config(dataset, version)
         elif isinstance(dataset, AbstractDataset):

kedro/io/core.py

@@ -113,6 +113,13 @@ class AbstractDataset(abc.ABC, Generic[_DI, _DO]):
             # param2 will be True by default
     """
 
+    """
+    Datasets are persistent by default. User-defined datasets that
+    are not made to be persistent, such as instances of `MemoryDataset`,
+    need to change the `_EPHEMERAL` attribute to 'True'.
+    """
+    _EPHEMERAL = False
+
     @classmethod
     def from_config(
         cls: type,

kedro/io/lambda_dataset.py

@@ -99,7 +99,6 @@ def __init__(  # noqa: PLR0913
             DatasetError: If a method is specified, but is not a Callable.
 
         """
-
         for name, value in [
             ("load", load),
             ("save", save),

kedro/io/memory_dataset.py

@@ -12,7 +12,8 @@
 
 class MemoryDataset(AbstractDataset):
     """``MemoryDataset`` loads and saves data from/to an in-memory
-    Python object.
+    Python object. The `_EPHEMERAL` attribute is set to True to
+    indicate MemoryDataset's non-persistence.
 
     Example:
     ::
@@ -54,6 +55,7 @@ def __init__(
         self._data = _EMPTY
         self._copy_mode = copy_mode
         self.metadata = metadata
+        self._EPHEMERAL = True
         if data is not _EMPTY:
             self._save(data)
 

kedro/io/shared_memory_dataset.py

@@ -18,6 +18,8 @@ def __init__(self, manager: SyncManager | None = None):
             manager: An instance of multiprocessing manager for shared objects.
 
         """
+        self._EPHEMERAL = True
+
         if manager:
             self.shared_memory_dataset = manager.MemoryDataset()  # type: ignore[attr-defined]
         else:

tests/io/test_cached_dataset.py

@@ -45,6 +45,9 @@ def test_load_empty(self, cached_ds):
         with pytest.raises(DatasetError, match=r"has not been saved yet"):
             _ = cached_ds.load()
 
+    def test_ephemeral_attribute(self, cached_ds):
+        assert cached_ds._EPHEMERAL is True
+
     def test_save_load(self, cached_ds):
         cached_ds.save(42)
         assert cached_ds.load() == 42

tests/io/test_lambda_dataset.py

@@ -52,6 +52,10 @@ def _dummy_release():
     assert actual == expected
 
 
+def test_ephemeral_attribute(mocked_dataset):
+    assert mocked_dataset._EPHEMERAL is False
+
+
 class TestLambdaDatasetLoad:
     def test_load_invocation(self, mocker):
         """Test the basic `load` method invocation"""

tests/io/test_memory_dataset.py

@@ -54,6 +54,9 @@ def test_load_none(self):
         loaded_data = MemoryDataset(None).load()
         assert loaded_data is None
 
+    def test_ephemeral_attribute(self, memory_dataset):
+        assert memory_dataset._EPHEMERAL is True
+
     def test_load_infer_mode(
         self, memory_dataset, input_data, mocked_infer_mode, mocked_copy_with_mode
     ):

tests/io/test_shared_memory_dataset.py

@@ -13,6 +13,9 @@ def shared_memory_dataset():
 
 
 class TestSharedMemoryDataset:
+    def test_ephemeral_attribute(self, shared_memory_dataset):
+        assert shared_memory_dataset._EPHEMERAL is True
+
     def test_save_and_load(self, shared_memory_dataset, input_data):
         """Test basic load"""
         shared_memory_dataset.save(input_data)