add tar.xz archive handler (#1361)

* add tar.xz archive handler

* update unittest for tar.xz archive

* remove .tar.xz unittest

* add separate .tar.xz unittest

* update PY2 compatibility

test/test_datasets_utils.py

@@ -100,6 +100,23 @@ class Tester(unittest.TestCase):
                             data = nf.read()
                         self.assertEqual(data, 'this is the content')
 
+    @unittest.skipIf('win' in sys.platform, 'temporarily disabled on Windows')
+    @unittest.skipIf(sys.version_info < (3,), "Extracting .tar.xz files is not supported under Python 2.x")
+    def test_extract_tar_xz(self):
+        for ext, mode in zip(['.tar.xz'], ['w:xz']):
+            with get_tmp_dir() as temp_dir:
+                with tempfile.NamedTemporaryFile() as bf:
+                    bf.write("this is the content".encode())
+                    bf.seek(0)
+                    with tempfile.NamedTemporaryFile(suffix=ext) as f:
+                        with tarfile.open(f.name, mode=mode) as zf:
+                            zf.add(bf.name, arcname='file.tst')
+                        utils.extract_archive(f.name, temp_dir)
+                        self.assertTrue(os.path.exists(os.path.join(temp_dir, 'file.tst')))
+                        with open(os.path.join(temp_dir, 'file.tst'), 'r') as nf:
+                            data = nf.read()
+                        self.assertEqual(data, 'this is the content')
+
     @unittest.skipIf('win' in sys.platform, 'temporarily disabled on Windows')
     def test_extract_gzip(self):
         with get_tmp_dir() as temp_dir:

torchvision/datasets/utils.py

@@ -8,6 +8,7 @@ import zipfile
 
 import torch
 from torch.utils.model_zoo import tqdm
+from torch._six import PY3
 
 
 def gen_bar_updater():
@@ -197,6 +198,10 @@ def _save_response_content(response, destination, chunk_size=32768):
         pbar.close()
 
 
+def _is_tarxz(filename):
+    return filename.endswith(".tar.xz")
+
+
 def _is_tar(filename):
     return filename.endswith(".tar")
 
@@ -223,6 +228,10 @@ def extract_archive(from_path, to_path=None, remove_finished=False):
     elif _is_targz(from_path):
         with tarfile.open(from_path, 'r:gz') as tar:
             tar.extractall(path=to_path)
+    elif _is_tarxz(from_path) and PY3:
+        # .tar.xz archive only supported in Python 3.x  
+        with tarfile.open(from_path, 'r:xz') as tar:
+            tar.extractall(path=to_path)
     elif _is_gzip(from_path):
         to_path = os.path.join(to_path, os.path.splitext(os.path.basename(from_path))[0])
         with open(to_path, "wb") as out_f, gzip.GzipFile(from_path) as zip_f: