style: Added typing to datasets/lfw (#6844)

Co-authored-by: Philip Meier <github.pmeier@posteo.de>

torchvision/datasets/lfw.py

 import os
-from typing import Any, Callable, List, Optional, Tuple
+from typing import Any, Callable, Dict, List, Optional, Tuple, Union
 
 from PIL import Image
 
@@ -38,7 +38,7 @@ class _LFW(VisionDataset):
         transform: Optional[Callable] = None,
         target_transform: Optional[Callable] = None,
         download: bool = False,
-    ):
+    ) -> None:
         super().__init__(os.path.join(root, self.base_folder), transform=transform, target_transform=target_transform)
 
         self.image_set = verify_str_arg(image_set.lower(), "image_set", self.file_dict.keys())
@@ -62,7 +62,7 @@ class _LFW(VisionDataset):
             img = Image.open(f)
             return img.convert("RGB")
 
-    def _check_integrity(self):
+    def _check_integrity(self) -> bool:
         st1 = check_integrity(os.path.join(self.root, self.filename), self.md5)
         st2 = check_integrity(os.path.join(self.root, self.labels_file), self.checksums[self.labels_file])
         if not st1 or not st2:
@@ -71,7 +71,7 @@ class _LFW(VisionDataset):
             return check_integrity(os.path.join(self.root, self.names), self.checksums[self.names])
         return True
 
-    def download(self):
+    def download(self) -> None:
         if self._check_integrity():
             print("Files already downloaded and verified")
             return
@@ -81,13 +81,13 @@ class _LFW(VisionDataset):
         if self.view == "people":
             download_url(f"{self.download_url_prefix}{self.names}", self.root)
 
-    def _get_path(self, identity, no):
+    def _get_path(self, identity: str, no: Union[int, str]) -> str:
         return os.path.join(self.images_dir, identity, f"{identity}_{int(no):04d}.jpg")
 
     def extra_repr(self) -> str:
         return f"Alignment: {self.image_set}\nSplit: {self.split}"
 
-    def __len__(self):
+    def __len__(self) -> int:
         return len(self.data)
 
 
@@ -119,13 +119,13 @@ class LFWPeople(_LFW):
         transform: Optional[Callable] = None,
         target_transform: Optional[Callable] = None,
         download: bool = False,
-    ):
+    ) -> None:
         super().__init__(root, split, image_set, "people", transform, target_transform, download)
 
         self.class_to_idx = self._get_classes()
         self.data, self.targets = self._get_people()
 
-    def _get_people(self):
+    def _get_people(self) -> Tuple[List[str], List[int]]:
         data, targets = [], []
         with open(os.path.join(self.root, self.labels_file)) as f:
             lines = f.readlines()
@@ -143,7 +143,7 @@ class LFWPeople(_LFW):
 
         return data, targets
 
-    def _get_classes(self):
+    def _get_classes(self) -> Dict[str, int]:
         with open(os.path.join(self.root, self.names)) as f:
             lines = f.readlines()
             names = [line.strip().split()[0] for line in lines]
@@ -201,12 +201,12 @@ class LFWPairs(_LFW):
         transform: Optional[Callable] = None,
         target_transform: Optional[Callable] = None,
         download: bool = False,
-    ):
+    ) -> None:
         super().__init__(root, split, image_set, "pairs", transform, target_transform, download)
 
         self.pair_names, self.data, self.targets = self._get_pairs(self.images_dir)
 
-    def _get_pairs(self, images_dir):
+    def _get_pairs(self, images_dir: str) -> Tuple[List[Tuple[str, str]], List[Tuple[str, str]], List[int]]:
         pair_names, data, targets = [], [], []
         with open(os.path.join(self.root, self.labels_file)) as f:
             lines = f.readlines()