[Python-checkins] bpo-44471: Change error type for bad objects in ExitStack.enter_context() (GH-26820)
serhiy-storchaka
webhook-mailer at python.org
Tue Jun 29 04:28:24 EDT 2021
https://github.com/python/cpython/commit/6cb145d23f5cf69b6d7414877d142747cd3d134c
commit: 6cb145d23f5cf69b6d7414877d142747cd3d134c
branch: main
author: Serhiy Storchaka <storchaka at gmail.com>
committer: serhiy-storchaka <storchaka at gmail.com>
date: 2021-06-29T11:28:15+03:00
summary:
bpo-44471: Change error type for bad objects in ExitStack.enter_context() (GH-26820)
A TypeError is now raised instead of an AttributeError in
ExitStack.enter_context() and AsyncExitStack.enter_async_context()
for objects which do not support the context manager or
asynchronous context manager protocols correspondingly.
files:
A Misc/NEWS.d/next/Library/2021-06-21-10-46-58.bpo-44471.2QjXv_.rst
M Doc/library/contextlib.rst
M Doc/whatsnew/3.11.rst
M Lib/contextlib.py
M Lib/test/test_contextlib.py
M Lib/test/test_contextlib_async.py
diff --git a/Doc/library/contextlib.rst b/Doc/library/contextlib.rst
index c9065be32e638..7ac3856819593 100644
--- a/Doc/library/contextlib.rst
+++ b/Doc/library/contextlib.rst
@@ -515,6 +515,10 @@ Functions and classes provided:
These context managers may suppress exceptions just as they normally
would if used directly as part of a :keyword:`with` statement.
+ ... versionchanged:: 3.11
+ Raises :exc:`TypeError` instead of :exc:`AttributeError` if *cm*
+ is not a context manager.
+
.. method:: push(exit)
Adds a context manager's :meth:`__exit__` method to the callback stack.
@@ -585,6 +589,10 @@ Functions and classes provided:
Similar to :meth:`enter_context` but expects an asynchronous context
manager.
+ ... versionchanged:: 3.11
+ Raises :exc:`TypeError` instead of :exc:`AttributeError` if *cm*
+ is not an asynchronous context manager.
+
.. method:: push_async_exit(exit)
Similar to :meth:`push` but expects either an asynchronous context manager
diff --git a/Doc/whatsnew/3.11.rst b/Doc/whatsnew/3.11.rst
index be1423b9f44b3..0ee4d29227a50 100644
--- a/Doc/whatsnew/3.11.rst
+++ b/Doc/whatsnew/3.11.rst
@@ -75,6 +75,12 @@ New Features
Other Language Changes
======================
+A :exc:`TypeError` is now raised instead of an :exc:`AttributeError` in
+:meth:`contextlib.ExitStack.enter_context` and
+:meth:`contextlib.AsyncExitStack.enter_async_context` for objects which do not
+support the :term:`context manager` or :term:`asynchronous context manager`
+protocols correspondingly.
+(Contributed by Serhiy Storchaka in :issue:`44471`.)
* A :exc:`TypeError` is now raised instead of an :exc:`AttributeError` in
:keyword:`with` and :keyword:`async with` statements for objects which do not
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index 1a8ef6122c8d4..004d1037b78a4 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -473,9 +473,14 @@ def enter_context(self, cm):
"""
# We look up the special methods on the type to match the with
# statement.
- _cm_type = type(cm)
- _exit = _cm_type.__exit__
- result = _cm_type.__enter__(cm)
+ cls = type(cm)
+ try:
+ _enter = cls.__enter__
+ _exit = cls.__exit__
+ except AttributeError:
+ raise TypeError(f"'{cls.__module__}.{cls.__qualname__}' object does "
+ f"not support the context manager protocol") from None
+ result = _enter(cm)
self._push_cm_exit(cm, _exit)
return result
@@ -600,9 +605,15 @@ async def enter_async_context(self, cm):
If successful, also pushes its __aexit__ method as a callback and
returns the result of the __aenter__ method.
"""
- _cm_type = type(cm)
- _exit = _cm_type.__aexit__
- result = await _cm_type.__aenter__(cm)
+ cls = type(cm)
+ try:
+ _enter = cls.__aenter__
+ _exit = cls.__aexit__
+ except AttributeError:
+ raise TypeError(f"'{cls.__module__}.{cls.__qualname__}' object does "
+ f"not support the asynchronous context manager protocol"
+ ) from None
+ result = await _enter(cm)
self._push_async_cm_exit(cm, _exit)
return result
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index dbc3f5fbe2b27..9c27866cd661c 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -661,6 +661,25 @@ def _exit():
result.append(2)
self.assertEqual(result, [1, 2, 3, 4])
+ def test_enter_context_errors(self):
+ class LacksEnterAndExit:
+ pass
+ class LacksEnter:
+ def __exit__(self, *exc_info):
+ pass
+ class LacksExit:
+ def __enter__(self):
+ pass
+
+ with self.exit_stack() as stack:
+ with self.assertRaisesRegex(TypeError, 'the context manager'):
+ stack.enter_context(LacksEnterAndExit())
+ with self.assertRaisesRegex(TypeError, 'the context manager'):
+ stack.enter_context(LacksEnter())
+ with self.assertRaisesRegex(TypeError, 'the context manager'):
+ stack.enter_context(LacksExit())
+ self.assertFalse(stack._exit_callbacks)
+
def test_close(self):
result = []
with self.exit_stack() as stack:
@@ -886,9 +905,11 @@ def test_excessive_nesting(self):
def test_instance_bypass(self):
class Example(object): pass
cm = Example()
+ cm.__enter__ = object()
cm.__exit__ = object()
stack = self.exit_stack()
- self.assertRaises(AttributeError, stack.enter_context, cm)
+ with self.assertRaisesRegex(TypeError, 'the context manager'):
+ stack.enter_context(cm)
stack.push(cm)
self.assertIs(stack._exit_callbacks[-1][1], cm)
diff --git a/Lib/test/test_contextlib_async.py b/Lib/test/test_contextlib_async.py
index cbc82dfd8f8d0..7904abff7d1aa 100644
--- a/Lib/test/test_contextlib_async.py
+++ b/Lib/test/test_contextlib_async.py
@@ -483,7 +483,7 @@ async def __aexit__(self, *exc_details):
1/0
@_async_test
- async def test_async_enter_context(self):
+ async def test_enter_async_context(self):
class TestCM(object):
async def __aenter__(self):
result.append(1)
@@ -504,6 +504,26 @@ async def _exit():
self.assertEqual(result, [1, 2, 3, 4])
+ @_async_test
+ async def test_enter_async_context_errors(self):
+ class LacksEnterAndExit:
+ pass
+ class LacksEnter:
+ async def __aexit__(self, *exc_info):
+ pass
+ class LacksExit:
+ async def __aenter__(self):
+ pass
+
+ async with self.exit_stack() as stack:
+ with self.assertRaisesRegex(TypeError, 'asynchronous context manager'):
+ await stack.enter_async_context(LacksEnterAndExit())
+ with self.assertRaisesRegex(TypeError, 'asynchronous context manager'):
+ await stack.enter_async_context(LacksEnter())
+ with self.assertRaisesRegex(TypeError, 'asynchronous context manager'):
+ await stack.enter_async_context(LacksExit())
+ self.assertFalse(stack._exit_callbacks)
+
@_async_test
async def test_async_exit_exception_chaining(self):
# Ensure exception chaining matches the reference behaviour
@@ -536,6 +556,18 @@ async def suppress_exc(*exc_details):
self.assertIsInstance(inner_exc, ValueError)
self.assertIsInstance(inner_exc.__context__, ZeroDivisionError)
+ @_async_test
+ async def test_instance_bypass_async(self):
+ class Example(object): pass
+ cm = Example()
+ cm.__aenter__ = object()
+ cm.__aexit__ = object()
+ stack = self.exit_stack()
+ with self.assertRaisesRegex(TypeError, 'asynchronous context manager'):
+ await stack.enter_async_context(cm)
+ stack.push_async_exit(cm)
+ self.assertIs(stack._exit_callbacks[-1][1], cm)
+
class TestAsyncNullcontext(unittest.TestCase):
@_async_test
diff --git a/Misc/NEWS.d/next/Library/2021-06-21-10-46-58.bpo-44471.2QjXv_.rst b/Misc/NEWS.d/next/Library/2021-06-21-10-46-58.bpo-44471.2QjXv_.rst
new file mode 100644
index 0000000000000..0675ef3262a09
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-06-21-10-46-58.bpo-44471.2QjXv_.rst
@@ -0,0 +1,5 @@
+A :exc:`TypeError` is now raised instead of an :exc:`AttributeError` in
+:meth:`contextlib.ExitStack.enter_context` and
+:meth:`contextlib.AsyncExitStack.enter_async_context` for objects which do
+not support the :term:`context manager` or :term:`asynchronous context
+manager` protocols correspondingly.
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