Cleaned-up imports in test files related to datasets (#3720)

test/datasets_utils.py

-import collections.abc
 import contextlib
 import functools
 import importlib
@@ -15,7 +14,6 @@ from typing import Any, Callable, Dict, Iterator, List, Optional, Sequence, Tupl
 
 import PIL
 import PIL.Image
-
 import torch
 import torchvision.datasets
 import torchvision.io

test/fakedata_generation.py

 import os
 import contextlib
+import hashlib
+import pickle
+import re
 import tarfile
-import json
+import unittest.mock
+from distutils import dir_util
+
 import numpy as np
 import PIL
 import torch
+
 from common_utils import get_tmp_dir
-import pickle
-import random
-from itertools import cycle
-from torchvision.io.video import write_video
-import unittest.mock
-import hashlib
-from distutils import dir_util
-import re
 
 
 def mock_class_attribute(stack, target, new):

test/test_datasets.py

+import bz2
 import contextlib
-import sys
-import os
-import unittest
-import numpy as np
-import PIL
-from PIL import Image
-from torch._utils_internal import get_file_path_2
-import torchvision
-from torchvision.datasets import utils
-from common_utils import get_tmp_dir
-import xml.etree.ElementTree as ET
-from urllib.request import Request, urlopen
+import io
 import itertools
-import datasets_utils
+import os
 import pathlib
 import pickle
-from torchvision import datasets
-import torch
-import shutil
 import json
 import random
-import bz2
-import torch.nn.functional as F
+import shutil
 import string
-import io
+import unittest
+import xml.etree.ElementTree as ET
 import zipfile
 
+import PIL
+import datasets_utils
+import numpy as np
+import torch
+import torch.nn.functional as F
+from torchvision import datasets
 
 try:
     import scipy
@@ -33,12 +26,6 @@ try:
 except ImportError:
     HAS_SCIPY = False
 
-try:
-    import av
-    HAS_PYAV = True
-except ImportError:
-    HAS_PYAV = False
-
 
 class STL10TestCase(datasets_utils.ImageDatasetTestCase):
     DATASET_CLASS = datasets.STL10
@@ -946,7 +933,7 @@ class LSUNTestCase(datasets_utils.ImageDatasetTestCase):
                 key = "".join(random.choice(hexdigits_lowercase) for _ in range(40)).encode()
 
                 buffer = io.BytesIO()
-                Image.open(file).save(buffer, format)
+                PIL.Image.open(file).save(buffer, format)
                 buffer.seek(0)
                 value = buffer.read()