add typehints to torchvision.datasets.sbu (#2536)

torchvision/datasets/sbu.py

 from PIL import Image
 from .utils import download_url, check_integrity
+from typing import Any, Callable, Optional, Tuple
 
 import os
 from .vision import VisionDataset
@@ -23,7 +24,13 @@ class SBU(VisionDataset):
     filename = "SBUCaptionedPhotoDataset.tar.gz"
     md5_checksum = '9aec147b3488753cf758b4d493422285'
 
-    def __init__(self, root, transform=None, target_transform=None, download=True):
+    def __init__(
+            self,
+            root: str,
+            transform: Optional[Callable] = None,
+            target_transform: Optional[Callable] = None,
+            download: bool = True,
+    ) -> None:
         super(SBU, self).__init__(root, transform=transform,
                                   target_transform=target_transform)
 
@@ -50,7 +57,7 @@ class SBU(VisionDataset):
                 self.photos.append(photo)
                 self.captions.append(caption)
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Tuple[Any, Any]:
         """
         Args:
             index (int): Index
@@ -69,11 +76,11 @@ class SBU(VisionDataset):
 
         return img, target
 
-    def __len__(self):
+    def __len__(self) -> int:
         """The number of photos in the dataset."""
         return len(self.photos)
 
-    def _check_integrity(self):
+    def _check_integrity(self) -> bool:
         """Check the md5 checksum of the downloaded tarball."""
         root = self.root
         fpath = os.path.join(root, self.filename)
@@ -81,7 +88,7 @@ class SBU(VisionDataset):
             return False
         return True
 
-    def download(self):
+    def download(self) -> None:
         """Download and extract the tarball, and download each individual photo."""
         import tarfile