From fb27885fcc50cfebd13865a8267e05daee7bb933 Mon Sep 17 00:00:00 2001
From: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Date: Wed, 3 May 2017 20:41:14 -0700
Subject: [PATCH 1/2] bpo-30266: support "= None" pattern in
 AbstractContextManager

---
 Lib/contextlib.py           |  5 ++---
 Lib/test/test_contextlib.py | 10 ++++++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index c53b35e8d5adaa..962cedab490eb2 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -1,6 +1,7 @@
 """Utilities for with-statement contexts.  See PEP 343."""
 import abc
 import sys
+import _collections_abc
 from collections import deque
 from functools import wraps
 
@@ -25,9 +26,7 @@ def __exit__(self, exc_type, exc_value, traceback):
     @classmethod
     def __subclasshook__(cls, C):
         if cls is AbstractContextManager:
-            if (any("__enter__" in B.__dict__ for B in C.__mro__) and
-                any("__exit__" in B.__dict__ for B in C.__mro__)):
-                return True
+            return _collections_abc._check_methods(C, "__enter__", "__exit__")
         return NotImplemented
 
 
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index b1a467d952da0f..2301f759d80858 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -44,6 +44,16 @@ def __exit__(self, *args):
 
         self.assertTrue(issubclass(DefaultEnter, AbstractContextManager))
 
+        class NoEnter(ManagerFromScratch):
+            __enter__ = None
+
+        self.assertFalse(issubclass(NoEnter, AbstractContextManager))
+
+        class NoExit(ManagerFromScratch):
+            __exit__ = None
+
+        self.assertFalse(issubclass(NoExit, AbstractContextManager))
+
 
 class ContextManagerTestCase(unittest.TestCase):
 

From 47262826c9c64e3deaa58df359b275955028c69c Mon Sep 17 00:00:00 2001
From: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Date: Thu, 4 May 2017 21:20:50 -0700
Subject: [PATCH 2/2] add Misc/NEWS entry

---
 Misc/NEWS | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Misc/NEWS b/Misc/NEWS
index 4e85c0fbf2abb9..56cd993b4dbbeb 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -317,6 +317,10 @@ Extension Modules
 Library
 -------
 
+- bpo-30266: contextlib.AbstractContextManager now supports anti-registration
+  by setting __enter__ = None or __exit__ = None, following the pattern
+  introduced in bpo-25958. Patch by Jelle Zijlstra.
+
 - bpo-30103: binascii.b2a_uu() and uu.encode() now support using ``'`'``
   as zero instead of space.