bpo-30266: support "= None" pattern in AbstractContextManager (GH-1448) (GH-2054)
contextlib.AbstractContextManager now supports anti-registration
by setting __enter__ = None or __exit__ = None, following the pattern
introduced in bpo-25958..
(cherry picked from commit 57161aac5eb9bcb0b43e551a1937ff0a84c1ec52)
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index 5e47054..6fcba9c 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 @@
@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 b1a467d..2301f75 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -44,6 +44,16 @@
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):
diff --git a/Misc/NEWS b/Misc/NEWS
index 213a6e9..e651769 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -96,6 +96,10 @@
- bpo-30048: Fixed ``Task.cancel()`` can be ignored when the task is
running coroutine and the coroutine returned without any more ``await``.
+- 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-30298: Weaken the condition of deprecation warnings for inline modifiers.
Now allowed several subsequential inline modifiers at the start of the
pattern (e.g. ``'(?i)(?s)...'``). In verbose mode whitespaces and comments