!6451 check if partition file exists when usage is not all in CelebADataset

Merge pull request !6451 from yanghaitao/yht_celeba_log

mindspore/dataset/engine/datasets.py

@@ -4940,6 +4940,12 @@ class CelebADataset(MappableDataset):
         self.shard_id = shard_id
         self.shuffle_level = shuffle
 
+        if usage != "all":
+            dir = os.path.realpath(self.dataset_dir)
+            partition_file = os.path.join(dir, "list_eval_partition.txt")
+            if os.path.exists(partition_file) is False:
+                raise RuntimeError("Partition file can not be found when usage is not 'all'.")
+
     def get_args(self):
         args = super().get_args()
         args["dataset_dir"] = self.dataset_dir