fix(mge/data): create dir automatically when download=True

GitOrigin-RevId: f3cb1b7d50af84c8c03b048ad3a0ad02e3c463f2

python_module/megengine/data/dataset/vision/cifar.py

@@ -57,7 +57,14 @@ class CIFAR10(VisionDataset):
         else:
             self.root = root
             if not os.path.exists(self.root):
-                raise ValueError("dir %s does not exist" % self.root)
+                if download:
+                    logger.debug(
+                        "dir %s does not exist, will be automatically created",
+                        self.root,
+                    )
+                    os.makedirs(self.root)
+                else:
+                    raise ValueError("dir %s does not exist" % self.root)
 
         self.target_file = os.path.join(self.root, self.raw_file_dir)
 
@@ -77,8 +84,7 @@ class CIFAR10(VisionDataset):
                     self.arrays = self.bytes2array(self.test_batch)
             else:
                 raise ValueError(
-                    "dir does not contain target file\
-                        %s, please set download=True"
+                    "dir does not contain target file %s, please set download=True"
                     % (self.target_file)
                 )
 
@@ -160,6 +166,6 @@ class CIFAR100(CIFAR10):
                 data.extend(list(batch_data[..., [2, 1, 0]]))
                 fine_label.extend(dic[b"fine_labels"])
                 coarse_label.extend(dic[b"coarse_labels"])
-        fine_label = np.array(fine_label)
-        coarse_label = np.array(coarse_label)
+        fine_label = np.array(fine_label, dtype=np.int32)
+        coarse_label = np.array(coarse_label, dtype=np.int32)
         return data, fine_label, coarse_label

python_module/megengine/data/dataset/vision/mnist.py

@@ -75,7 +75,14 @@ class MNIST(VisionDataset):
         else:
             self.root = root
             if not os.path.exists(self.root):
-                raise ValueError("dir %s does not exist" % self.root)
+                if download:
+                    logger.debug(
+                        "dir %s does not exist, will be automatically created",
+                        self.root,
+                    )
+                    os.makedirs(self.root)
+                else:
+                    raise ValueError("dir %s does not exist" % self.root)
 
         if self._check_raw_files():
             self.process(train)