Add partitioners property to FederatedDataset (#3096)

Co-authored-by: Javier <[email protected]>
Co-authored-by: Flower <[email protected]>

datasets/flwr_datasets/federated_dataset.py

@@ -213,6 +213,25 @@ def load_split(self, split: str) -> Dataset:
         self._check_if_split_present(split)
         return self._dataset[split]
 
+    @property
+    def partitioners(self) -> Dict[str, Partitioner]:
+        """Dictionary mapping each split to its associated partitioner.
+
+        The returned partitioners have the splits of the dataset assigned to them.
+        """
+        # This function triggers the dataset download (lazy download) and checks
+        # the partitioner specification correctness (which can also happen lazily only
+        # after the dataset download).
+        if not self._dataset_prepared:
+            self._prepare_dataset()
+        if self._dataset is None:
+            raise ValueError("Dataset is not loaded yet.")
+        partitioners_keys = list(self._partitioners.keys())
+        for split in partitioners_keys:
+            self._check_if_split_present(split)
+            self._assign_dataset_to_partitioner(split)
+        return self._partitioners
+
     def _check_if_split_present(self, split: str) -> None:
         """Check if the split (for partitioning or full return) is in the dataset."""
         if self._dataset is None: