Issue #25609: Introduce contextlib.AbstractContextManager and

typing.ContextManager.

2 files changed, 51 insertions, 0 deletions

diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 04fc875..5c8bc98 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -12,6 +12,39 @@ except ImportError:
     threading = None
 
 
+class TestAbstractContextManager(unittest.TestCase):
+
+    def test_enter(self):
+        class DefaultEnter(AbstractContextManager):
+            def __exit__(self, *args):
+                super().__exit__(*args)
+
+        manager = DefaultEnter()
+        self.assertIs(manager.__enter__(), manager)
+
+    def test_exit_is_abstract(self):
+        class MissingExit(AbstractContextManager):
+            pass
+
+        with self.assertRaises(TypeError):
+            MissingExit()
+
+    def test_structural_subclassing(self):
+        class ManagerFromScratch:
+            def __enter__(self):
+                return self
+            def __exit__(self, exc_type, exc_value, traceback):
+                return None
+
+        self.assertTrue(issubclass(ManagerFromScratch, AbstractContextManager))
+
+        class DefaultEnter(AbstractContextManager):
+            def __exit__(self, *args):
+                super().__exit__(*args)
+
+        self.assertTrue(issubclass(DefaultEnter, AbstractContextManager))
+
+
 class ContextManagerTestCase(unittest.TestCase):
 
     def test_contextmanager_plain(self):
diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index f1c6e12..a360824 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -1,3 +1,4 @@
+import contextlib
 import pickle
 import re
 import sys
@@ -1309,6 +1310,21 @@ class CollectionsAbcTests(TestCase):
         assert len(MMB[KT, VT]()) == 0
 
 
+class OtherABCTests(TestCase):
+
+    @skipUnless(hasattr(typing, 'ContextManager'),
+                'requires typing.ContextManager')
+    def test_contextmanager(self):
+        @contextlib.contextmanager
+        def manager():
+            yield 42
+
+        cm = manager()
+        assert isinstance(cm, typing.ContextManager)
+        assert isinstance(cm, typing.ContextManager[int])
+        assert not isinstance(42, typing.ContextManager)
+
+
 class NamedTupleTests(TestCase):
 
     def test_basics(self):
@@ -1447,6 +1463,8 @@ class AllTests(TestCase):
         assert 'ValuesView' in a
         assert 'cast' in a
         assert 'overload' in a
+        if hasattr(contextlib, 'AbstractContextManager'):
+            assert 'ContextManager' in a
         # Check that io and re are not exported.
         assert 'io' not in a
         assert 're' not in a