add typehints for torchvision.datasets.stl10 (#2540)

* add typehints for torchvision.datasets.stl10

* move annotation from class to instance scope

torchvision/datasets/stl10.py

@@ -2,6 +2,7 @@ from PIL import Image
 import os
 import os.path
 import numpy as np
+from typing import Any, Callable, Optional, Tuple
 
 from .vision import VisionDataset
 from .utils import check_integrity, download_and_extract_archive, verify_str_arg
@@ -45,8 +46,15 @@ class STL10(VisionDataset):
     ]
     splits = ('train', 'train+unlabeled', 'unlabeled', 'test')
 
-    def __init__(self, root, split='train', folds=None, transform=None,
-                 target_transform=None, download=False):
+    def __init__(
+            self,
+            root: str,
+            split: str = "train",
+            folds: Optional[int] = None,
+            transform: Optional[Callable] = None,
+            target_transform: Optional[Callable] = None,
+            download: bool = False,
+    ) -> None:
         super(STL10, self).__init__(root, transform=transform,
                                     target_transform=target_transform)
         self.split = verify_str_arg(split, "split", self.splits)
@@ -60,6 +68,7 @@ class STL10(VisionDataset):
                 'You can use download=True to download it')
 
         # now load the picked numpy arrays
+        self.labels: np.ndarray
         if self.split == 'train':
             self.data, self.labels = self.__loadfile(
                 self.train_list[0][0], self.train_list[1][0])
@@ -87,7 +96,7 @@ class STL10(VisionDataset):
             with open(class_file) as f:
                 self.classes = f.read().splitlines()
 
-    def _verify_folds(self, folds):
+    def _verify_folds(self, folds: Optional[int]) -> Optional[int]:
         if folds is None:
             return folds
         elif isinstance(folds, int):
@@ -100,7 +109,7 @@ class STL10(VisionDataset):
             msg = "Expected type None or int for argument folds, but got type {}."
             raise ValueError(msg.format(type(folds)))
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Tuple[Any, Any]:
         """
         Args:
             index (int): Index
@@ -108,6 +117,7 @@ class STL10(VisionDataset):
         Returns:
             tuple: (image, target) where target is index of the target class.
         """
+        target: Optional[int]
         if self.labels is not None:
             img, target = self.data[index], int(self.labels[index])
         else:
@@ -125,10 +135,10 @@ class STL10(VisionDataset):
 
         return img, target
 
-    def __len__(self):
+    def __len__(self) -> int:
         return self.data.shape[0]
 
-    def __loadfile(self, data_file, labels_file=None):
+    def __loadfile(self, data_file: str, labels_file: Optional[str] = None) -> Tuple[np.ndarray, Optional[np.ndarray]]:
         labels = None
         if labels_file:
             path_to_labels = os.path.join(
@@ -145,7 +155,7 @@ class STL10(VisionDataset):
 
         return images, labels
 
-    def _check_integrity(self):
+    def _check_integrity(self) -> bool:
         root = self.root
         for fentry in (self.train_list + self.test_list):
             filename, md5 = fentry[0], fentry[1]
@@ -154,17 +164,17 @@ class STL10(VisionDataset):
                 return False
         return True
 
-    def download(self):
+    def download(self) -> None:
         if self._check_integrity():
             print('Files already downloaded and verified')
             return
         download_and_extract_archive(self.url, self.root, filename=self.filename, md5=self.tgz_md5)
         self._check_integrity()
 
-    def extra_repr(self):
+    def extra_repr(self) -> str:
         return "Split: {split}".format(**self.__dict__)
 
-    def __load_folds(self, folds):
+    def __load_folds(self, folds: Optional[int]) -> None:
         # loads one of the folds if specified
         if folds is None:
             return