Context managers (#13900)

* add `ContextManagers` for lists of contexts

* fix import sorting

* add `ContextManagers` tests

tests/test_file_utils.py

@@ -12,7 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import contextlib
 import importlib
+import io
 import unittest
 
 import requests
@@ -20,7 +22,14 @@ import transformers
 
 # Try to import everything from transformers to ensure every object can be loaded.
 from transformers import *  # noqa F406
-from transformers.file_utils import CONFIG_NAME, WEIGHTS_NAME, filename_to_url, get_from_cache, hf_bucket_url
+from transformers.file_utils import (
+    CONFIG_NAME,
+    WEIGHTS_NAME,
+    ContextManagers,
+    filename_to_url,
+    get_from_cache,
+    hf_bucket_url,
+)
 from transformers.testing_utils import DUMMY_UNKNOWN_IDENTIFIER
 
 
@@ -40,6 +49,21 @@ PINNED_SHA256 = "4b243c475af8d0a7754e87d7d096c92e5199ec2fe168a2ee7998e3b8e9bcb1d
 # Sha-256 of pytorch_model.bin on the top of `main`, for checking purposes
 
 
+# Dummy contexts to test `ContextManagers`
+@contextlib.contextmanager
+def context_en():
+    print("Welcome!")
+    yield
+    print("Bye!")
+
+
+@contextlib.contextmanager
+def context_fr():
+    print("Bonjour!")
+    yield
+    print("Au revoir!")
+
+
 def test_module_spec():
     assert transformers.__spec__ is not None
     assert importlib.util.find_spec("transformers") is not None
@@ -85,3 +109,26 @@ class GetFromCacheTests(unittest.TestCase):
         filepath = get_from_cache(url, force_download=True)
         metadata = filename_to_url(filepath)
         self.assertEqual(metadata, (url, f'"{PINNED_SHA256}"'))
+
+
+class ContextManagerTests(unittest.TestCase):
+    @unittest.mock.patch("sys.stdout", new_callable=io.StringIO)
+    def test_no_context(self, mock_stdout):
+        with ContextManagers([]):
+            print("Transformers are awesome!")
+        # The print statement adds a new line at the end of the output
+        self.assertEqual(mock_stdout.getvalue(), "Transformers are awesome!\n")
+
+    @unittest.mock.patch("sys.stdout", new_callable=io.StringIO)
+    def test_one_context(self, mock_stdout):
+        with ContextManagers([context_en()]):
+            print("Transformers are awesome!")
+        # The output should be wrapped with an English welcome and goodbye
+        self.assertEqual(mock_stdout.getvalue(), "Welcome!\nTransformers are awesome!\nBye!\n")
+
+    @unittest.mock.patch("sys.stdout", new_callable=io.StringIO)
+    def test_two_context(self, mock_stdout):
+        with ContextManagers([context_fr(), context_en()]):
+            print("Transformers are awesome!")
+        # The output should be wrapped with an English and French welcome and goodbye
+        self.assertEqual(mock_stdout.getvalue(), "Bonjour!\nWelcome!\nTransformers are awesome!\nBye!\nAu revoir!\n")