fix: fix lsun dataset error message.

test/test_datasets.py

@@ -1056,6 +1056,50 @@ def test_not_found_or_corrupted(self):
         with pytest.raises(datasets_utils.lazy_importer.lmdb.Error):
             super().test_not_found_or_corrupted()
 
+    def test_class_name_verification(self):
+        err_msg = (
+            "Unknown value '{}' for LSUN class. "
+            "The valid value is one of 'train', 'val' or 'test' or a list of categories "
+            "e.g. ['bedroom_train', 'bedroom_val', 'bridge_train', 'bridge_val', "
+            "'church_outdoor_train', 'church_outdoor_val', 'classroom_train', 'classroom_val', "
+            "'conference_room_train', 'conference_room_val', 'dining_room_train', 'dining_room_val', "
+            "'kitchen_train', 'kitchen_val', 'living_room_train', 'living_room_val', "
+            "'restaurant_train', 'restaurant_val', 'tower_train', 'tower_val']."
+        )
+
+        cases = [
+            "bedroom",
+            "bedroom_train",
+        ]
+        for case in cases:
+            with pytest.raises(
+                ValueError,
+                match=re.escape(err_msg.format(case)),
+            ):
+                with self.create_dataset(classes=case):
+                    pass
+
+        for case in [
+            ["bedroom_train", "bedroom"],
+            ["bedroom_train", "bedroommmmmmmm_val"],
+        ]:
+            with pytest.raises(
+                ValueError,
+                match=re.escape(err_msg.format(case[-1])),
+            ):
+                with self.create_dataset(classes=case):
+                    pass
+
+        for case in [[None], [1]]:
+            with pytest.raises(
+                TypeError,
+                match=re.escape(
+                    f"Expected type str for elements in argument classes, but got type {type(case[0]).__name__}."
+                ),
+            ):
+                with self.create_dataset(classes=case):
+                    pass
+
 
 class KineticsTestCase(datasets_utils.VideoDatasetTestCase):
     DATASET_CLASS = datasets.Kinetics

torchvision/datasets/lsun.py

@@ -4,11 +4,11 @@
 import string
 from collections.abc import Iterable
 from pathlib import Path
-from typing import Any, Callable, cast, Optional, Union
+from typing import Any, Callable, Optional, Union
 
 from PIL import Image
 
-from .utils import iterable_to_str, verify_str_arg
+from .utils import verify_str_arg
 from .vision import VisionDataset
 
 
@@ -108,31 +108,45 @@ def _verify_classes(self, classes: Union[str, list[str]]) -> list[str]:
         ]
         dset_opts = ["train", "val", "test"]
 
-        try:
-            classes = cast(str, classes)
-            verify_str_arg(classes, "classes", dset_opts)
+        err_msg = (
+            "Unknown value '{classes}' for LSUN class. "
+            "The valid value is one of 'train', 'val' or 'test' or a list of categories "
+            "e.g. ['bedroom_train', 'bedroom_val', 'bridge_train', 'bridge_val', "
+            "'church_outdoor_train', 'church_outdoor_val', 'classroom_train', 'classroom_val', "
+            "'conference_room_train', 'conference_room_val', 'dining_room_train', 'dining_room_val', "
+            "'kitchen_train', 'kitchen_val', 'living_room_train', 'living_room_val', "
+            "'restaurant_train', 'restaurant_val', 'tower_train', 'tower_val']."
+        )
+
+        if isinstance(classes, str):
+            if classes not in dset_opts:
+                raise ValueError(err_msg.format(classes=classes))
+            # If classes is a string, it should be one of the dataset options
+            # and not a specific category.
             if classes == "test":
                 classes = [classes]
             else:
                 classes = [c + "_" + classes for c in categories]
-        except ValueError:
-            if not isinstance(classes, Iterable):
-                msg = "Expected type str or Iterable for argument classes, but got type {}."
-                raise ValueError(msg.format(type(classes)))
-
+        elif isinstance(classes, Iterable):
             classes = list(classes)
             msg_fmtstr_type = "Expected type str for elements in argument classes, but got type {}."
+
             for c in classes:
-                verify_str_arg(c, custom_msg=msg_fmtstr_type.format(type(c)))
+                if not isinstance(c, str):
+                    raise TypeError(msg_fmtstr_type.format(type(c).__name__))
+                msg = err_msg.format(classes=c)
+
                 c_short = c.split("_")
+                if len(c_short) < 2:
+                    raise ValueError(msg)
                 category, dset_opt = "_".join(c_short[:-1]), c_short[-1]
 
-                msg_fmtstr = "Unknown value '{}' for {}. Valid values are {{{}}}."
-                msg = msg_fmtstr.format(category, "LSUN class", iterable_to_str(categories))
                 verify_str_arg(category, valid_values=categories, custom_msg=msg)
-
-                msg = msg_fmtstr.format(dset_opt, "postfix", iterable_to_str(dset_opts))
                 verify_str_arg(dset_opt, valid_values=dset_opts, custom_msg=msg)
+        else:
+            raise TypeError(
+                f"Expected type str or Iterable for argument classes, but got type {type(classes).__name__}."
+            )
 
         return classes