add typehints for torchvision.datasets.usps (#2538)

torchvision/datasets/usps.py

 from PIL import Image
 import os
 import numpy as np
+from typing import Any, Callable, cast, Optional, Tuple
 
 from .utils import download_url
 from .vision import VisionDataset
@@ -36,8 +37,14 @@ class USPS(VisionDataset):
         ],
     }
 
-    def __init__(self, root, train=True, transform=None, target_transform=None,
-                 download=False):
+    def __init__(
+            self,
+            root: str,
+            train: bool = True,
+            transform: Optional[Callable] = None,
+            target_transform: Optional[Callable] = None,
+            download: bool = False,
+    ) -> None:
         super(USPS, self).__init__(root, transform=transform,
                                    target_transform=target_transform)
         split = 'train' if train else 'test'
@@ -52,13 +59,13 @@ class USPS(VisionDataset):
             raw_data = [line.decode().split() for line in fp.readlines()]
             imgs = [[x.split(':')[-1] for x in data[1:]] for data in raw_data]
             imgs = np.asarray(imgs, dtype=np.float32).reshape((-1, 16, 16))
-            imgs = ((imgs + 1) / 2 * 255).astype(dtype=np.uint8)
+            imgs = ((cast(np.ndarray, imgs) + 1) / 2 * 255).astype(dtype=np.uint8)
             targets = [int(d[0]) - 1 for d in raw_data]
 
         self.data = imgs
         self.targets = targets
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Tuple[Any, Any]:
         """
         Args:
             index (int): Index
@@ -80,5 +87,5 @@ class USPS(VisionDataset):
 
         return img, target
 
-    def __len__(self):
+    def __len__(self) -> int:
         return len(self.data)