Issue #25609: Introduce contextlib.AbstractContextManager and
typing.ContextManager.
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index 5377987..98903bc 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -1,11 +1,34 @@
"""Utilities for with-statement contexts. See PEP 343."""
-
+import abc
import sys
from collections import deque
from functools import wraps
-__all__ = ["contextmanager", "closing", "ContextDecorator", "ExitStack",
- "redirect_stdout", "redirect_stderr", "suppress"]
+__all__ = ["contextmanager", "closing", "AbstractContextManager",
+ "ContextDecorator", "ExitStack", "redirect_stdout",
+ "redirect_stderr", "suppress"]
+
+
+class AbstractContextManager(abc.ABC):
+
+ """An abstract base class for context managers."""
+
+ def __enter__(self):
+ """Return `self` upon entering the runtime context."""
+ return self
+
+ @abc.abstractmethod
+ def __exit__(self, exc_type, exc_value, traceback):
+ """Raise any exception triggered within the runtime context."""
+ return None
+
+ @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 NotImplemented
class ContextDecorator(object):
@@ -31,7 +54,7 @@
return inner
-class _GeneratorContextManager(ContextDecorator):
+class _GeneratorContextManager(ContextDecorator, AbstractContextManager):
"""Helper for @contextmanager decorator."""
def __init__(self, func, args, kwds):
@@ -134,7 +157,7 @@
return helper
-class closing(object):
+class closing(AbstractContextManager):
"""Context to automatically close something at the end of a block.
Code like this:
@@ -159,7 +182,7 @@
self.thing.close()
-class _RedirectStream:
+class _RedirectStream(AbstractContextManager):
_stream = None
@@ -199,7 +222,7 @@
_stream = "stderr"
-class suppress:
+class suppress(AbstractContextManager):
"""Context manager to suppress specified exceptions
After the exception is suppressed, execution proceeds with the next
@@ -230,7 +253,7 @@
# Inspired by discussions on http://bugs.python.org/issue13585
-class ExitStack(object):
+class ExitStack(AbstractContextManager):
"""Context manager for dynamic management of a stack of exit callbacks
For example:
@@ -309,9 +332,6 @@
"""Immediately unwind the context stack"""
self.__exit__(None, None, None)
- def __enter__(self):
- return self
-
def __exit__(self, *exc_details):
received_exc = exc_details[0] is not None
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 @@
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 @@
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 @@
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
diff --git a/Lib/typing.py b/Lib/typing.py
index 6ead3c4..42a9ea3 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1,6 +1,7 @@
import abc
from abc import abstractmethod, abstractproperty
import collections
+import contextlib
import functools
import re as stdlib_re # Avoid confusion with the re we export.
import sys
@@ -1530,6 +1531,12 @@
pass
+if hasattr(contextlib, 'AbstractContextManager'):
+ class ContextManager(Generic[T_co], extra=contextlib.AbstractContextManager):
+ __slots__ = ()
+ __all__.append('ContextManager')
+
+
class Dict(dict, MutableMapping[KT, VT]):
def __new__(cls, *args, **kwds):