Fix load data from disk (#910)

* Fix repo_id in load and make config argument optional if possible

* Add tests for LoadFromDisk

* Update src/distilabel/steps/generators/huggingface.py

Co-authored-by: Gabriel Martín Blázquez <gmartinbdev@gmail.com>

* Make error more informative

---------

Co-authored-by: Gabriel Martín Blázquez <gmartinbdev@gmail.com>

src/distilabel/steps/generators/huggingface.py

@@ -460,16 +460,16 @@ class LoadDataFromDisk(LoadDataFromHub):
     Attributes:
         dataset_path: The path to the dataset or distiset.
         split: The split of the dataset to load (typically will be `train`, `test` or `validation`).
-        config: The configuration of the dataset to load. This is optional and only needed
-            if the dataset has multiple configurations.
+        config: The configuration of the dataset to load. Defaults to `default`, if there are
+            multiple configurations in the dataset this must be suplied or an error is raised.
 
     Runtime parameters:
         - `batch_size`: The batch size to use when processing the data.
         - `dataset_path`: The path to the dataset or distiset.
         - `is_distiset`: Whether the dataset to load is a `Distiset` or not. Defaults to False.
         - `split`: The split of the dataset to load. Defaults to 'train'.
-        - `config`: The configuration of the dataset to load. This is optional and only
-            needed if the dataset has multiple configurations.
+        - `config`: The configuration of the dataset to load. Defaults to `default`, if there are
+            multiple configurations in the dataset this must be suplied or an error is raised.
         - `num_examples`: The number of examples to load from the dataset.
             By default will load all examples.
         - `storage_options`: Key/value pairs to be passed on to the file-system backend, if any.
@@ -539,10 +539,12 @@ class LoadDataFromDisk(LoadDataFromHub):
         default=None,
         description="Path to the dataset or distiset.",
     )
-    config: RuntimeParameter[str] = Field(
-        default=None,
-        description="The configuration of the dataset to load. This is optional and only"
-        " needed if the dataset has multiple configurations.",
+    config: Optional[RuntimeParameter[str]] = Field(
+        default="default",
+        description=(
+            "The configuration of the dataset to load. Will default to 'default'",
+            " which corresponds to a distiset with a single configuration.",
+        ),
     )
     is_distiset: Optional[RuntimeParameter[bool]] = Field(
         default=False,
@@ -557,6 +559,7 @@ class LoadDataFromDisk(LoadDataFromHub):
         default=None,
         description="The split of the dataset to load. By default will load the whole Dataset/Distiset.",
     )
+    repo_id: ExcludedField[Union[str, None]] = None
 
     def load(self) -> None:
         """Load the dataset from the file/s in disk."""
@@ -567,8 +570,15 @@ def load(self) -> None:
                 keep_in_memory=self.keep_in_memory,
                 storage_options=self.storage_options,
             )
-            if self.config:
-                ds = ds[self.config]
+            if self.config not in ds.keys():
+                # TODO: Add FAQ for this case, pointing to the Distiset documentation on configurations.
+                raise ValueError(
+                    f"Configuration '{self.config}' not found in the Distiset, available ones"
+                    f" are: {list(ds.keys())}. Please try changing the `config` parameter to one "
+                    "of the available configurations.\n\n"
+                    f"For more information on Distiset configurations, please visit https://distilabel.argilla.io/dev/sections/how_to_guides/advanced/distiset/#using-the-distiset-dataset-object"
+                )
+            ds = ds[self.config]
 
         else:
             ds = load_from_disk(
@@ -596,9 +606,7 @@ def outputs(self) -> List[str]:
             The columns that will be generated by this step.
         """
         # We assume there are Dataset/IterableDataset, not it's ...Dict counterparts
-        if self._dataset is Ellipsis:
-            raise ValueError(
-                "Dataset not loaded yet, you must call `load` method first."
-            )
+        if self._dataset is None:
+            self.load()
 
         return self._dataset.column_names

tests/unit/steps/generators/test_huggingface.py

@@ -168,6 +168,32 @@ def test_load_dataset_from_disk(self) -> None:
             assert isinstance(generator_step_output[1], bool)
             assert len(generator_step_output[0]) == 3
 
+    @pytest.mark.parametrize("config_name", ["default", "missnamed_config"])
+    def test_load_distiset_from_disk_default(self, config_name: str) -> None:
+        distiset = Distiset(
+            {
+                "default": Dataset.from_dict({"a": [1, 2, 3]}),
+            }
+        )
+        with tempfile.TemporaryDirectory() as tmpdir:
+            dataset_path = str(Path(tmpdir) / "dataset_path")
+            distiset.save_to_disk(dataset_path)
+
+            loader = LoadDataFromDisk(
+                dataset_path=dataset_path,
+                is_distiset=True,
+                config=config_name,
+            )
+            if config_name != "default":
+                with pytest.raises(ValueError):
+                    loader.load()
+            else:
+                loader.load()
+                generator_step_output = next(loader.process())
+                assert isinstance(generator_step_output, tuple)
+                assert isinstance(generator_step_output[1], bool)
+                assert len(generator_step_output[0]) == 3
+
     def test_load_distiset_from_disk(self) -> None:
         distiset = Distiset(
             {