bpo-39674: Revert "bpo-37330: open() no longer accept 'U' in file mode (GH-16959)" (GH-18767)

This reverts commit e471e72977c83664f13d041c78549140c86c92de.

The mode will be removed from Python 3.10.

1 files changed, 3 insertions, 15 deletions

diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index dcdd574bc7f..54a3520802a 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -712,23 +712,11 @@ class UTF16Test(ReadTest, unittest.TestCase):
         self.addCleanup(support.unlink, support.TESTFN)
         with open(support.TESTFN, 'wb') as fp:
             fp.write(s)
-        with codecs.open(support.TESTFN, 'r',
-                         encoding=self.encoding) as reader:
+        with support.check_warnings(('', DeprecationWarning)):
+            reader = codecs.open(support.TESTFN, 'U', encoding=self.encoding)
+        with reader:
             self.assertEqual(reader.read(), s1)
 
-    def test_invalid_modes(self):
-        for mode in ('U', 'rU', 'r+U'):
-            with self.assertRaises(ValueError) as cm:
-                codecs.open(support.TESTFN, mode, encoding=self.encoding)
-            self.assertIn('invalid mode', str(cm.exception))
-
-        for mode in ('rt', 'wt', 'at', 'r+t'):
-            with self.assertRaises(ValueError) as cm:
-                codecs.open(support.TESTFN, mode, encoding=self.encoding)
-            self.assertIn("can't have text and binary mode at once",
-                          str(cm.exception))
-
-
 class UTF16LETest(ReadTest, unittest.TestCase):
     encoding = "utf-16-le"
     ill_formed_sequence = b"\x80\xdc"