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gh-111375: Fix handling of exceptions within@contextmanager-decorated functions#111676
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0138ff1 Add sys._set_exception() to expose the `PyErr_SetHandledExecption` fu…
pR0Psb285e9a Fix exception context in @contextmanagers
pR0Psea784d7 Reference GH issue in comment
pR0Psbf4ef1e Add more checks for exception context
pR0Psbbc212b Fix sys._set_exception() docstring wording
pR0Ps59ef993 Fix test case and add explanation in comment
pR0Psc0e7400 Add exc_context parameter to {gen/coro}.throw()
pR0Ps5e8323a Move exc_context setting into _gen_throw and restore previous exception
pR0Psa7e2dc9 Default .throw()'s exc_context to the current exception
pR0Ps90fdbe0 Remove overactive assert
pR0Ps5da75d0 Rename test case
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -106,6 +106,7 @@ class _GeneratorContextManagerBase: | ||
| """Shared functionality for @contextmanager and @asynccontextmanager.""" | ||
| def __init__(self, func, args, kwds): | ||
| self.exc_context = None | ||
| self.gen = func(*args, **kwds) | ||
| self.func, self.args, self.kwds = func, args, kwds | ||
| # Issue 19330: ensure context manager instances have good docstrings | ||
| @@ -134,6 +135,8 @@ class _GeneratorContextManager( | ||
| """Helper for @contextmanager decorator.""" | ||
| def __enter__(self): | ||
| # store the exception context on enter so it can be restored on exit | ||
| self.exc_context = sys.exception() | ||
| # do not keep args and kwds alive unnecessarily | ||
| # they are only needed for recreation, which is not possible anymore | ||
| del self.args, self.kwds, self.func | ||
| @@ -143,6 +146,9 @@ def __enter__(self): | ||
| raise RuntimeError("generator didn't yield") from None | ||
| def __exit__(self, typ, value, traceback): | ||
| # don't keep the stored exception alive unnecessarily | ||
| exc_context = self.exc_context | ||
| self.exc_context = None | ||
| if typ is None: | ||
| try: | ||
| next(self.gen) | ||
| @@ -159,7 +165,13 @@ def __exit__(self, typ, value, traceback): | ||
| # tell if we get the same exception back | ||
| value = typ() | ||
| try: | ||
| # If the generator handles the exception thrown into it, the | ||
| # exception context reverts to the actual current exception | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others.Learn more. Now that I forgot everything I'm finding this comment less clear. What is "the actual current exception"? There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others.Learn more. Also, when you write "If X then Y", it's not immediately clear whether you are talking about what happens, what should happen, or what would happen if we didn't do what we're doing here. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others.Learn more. I definitely agree that it's not very clear, it's a bit of a complex issue to explain. How about this: # Throw the current exception into the generator so it can# handle it.# Once the generator handles the thrown exception, the# exception context within it should revert back to what it was# before its "yield" statement (ie. what it was in self.__enter__).# However, since we're still currently handling the exception# that we throw into the generator here, the exception context# in the generator wouldn't change.# To work around this, we forcefully set the current exception# context to be what it was just before the generator's yield# statement before throwing the current exception into it.# (see gh-111676). | ||
| # context here. In order to make the context manager behave | ||
| # like a normal function we set the current exception context | ||
| # to what it was during the context manager's __enter__ | ||
| # (see gh-111676). | ||
| self.gen.throw(value, exc_context=exc_context) | ||
| except StopIteration as exc: | ||
| # Suppress StopIteration *unless* it's the same exception that | ||
| # was passed to throw(). This prevents a StopIteration | ||
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -306,6 +306,98 @@ def woohoo(): | ||
| with woohoo(): | ||
| raise StopIteration | ||
| def test_contextmanager_handling_exception_resets_exc_info(self): | ||
| # Test that sys.exc_info() is correctly unset after handling the error | ||
| # when used within a context manager | ||
| @contextmanager | ||
| def ctx(reraise=False): | ||
| try: | ||
| self.assertIsNone(sys.exception()) | ||
| yield | ||
| except: | ||
| self.assertIsInstance(sys.exception(), ZeroDivisionError) | ||
| if reraise: | ||
| raise | ||
| else: | ||
| self.assertIsNone(sys.exception()) | ||
| self.assertIsNone(sys.exception()) | ||
| with ctx(): | ||
| pass | ||
| with ctx(): | ||
| 1/0 | ||
| with self.assertRaises(ZeroDivisionError): | ||
| with ctx(reraise=True): | ||
| 1/0 | ||
iritkatriel marked this conversation as resolved. Show resolvedHide resolvedUh oh!There was an error while loading.Please reload this page. | ||
| def test_contextmanager_preserves_handled_exception(self): | ||
| # test that any exceptions currently being handled are preserved | ||
| # through the context manager | ||
| @contextmanager | ||
| def ctx(reraise=False): | ||
| # called while handling an IndexError --> TypeError | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| self.assertIsInstance(sys.exception().__context__, IndexError) | ||
| exc_ctx = sys.exception() | ||
| try: | ||
| # raises a ValueError --> ZeroDivisionError | ||
| yield | ||
| except: | ||
| self.assertIsInstance(sys.exception(), ZeroDivisionError) | ||
| self.assertIsInstance(sys.exception().__context__, ValueError) | ||
| # original error context is preserved | ||
| self.assertIs(sys.exception().__context__.__context__, exc_ctx) | ||
| if reraise: | ||
| raise | ||
| # inner error handled, context should now be the original context | ||
| self.assertIs(sys.exception(), exc_ctx) | ||
| try: | ||
| raise IndexError() | ||
| except: | ||
| try: | ||
| raise TypeError() | ||
| except: | ||
| with ctx(): | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| self.assertIsInstance(sys.exception().__context__, IndexError) | ||
| try: | ||
| raise ValueError() | ||
| except: | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
| self.assertIsInstance(sys.exception().__context__, TypeError) | ||
| self.assertIsInstance(sys.exception().__context__.__context__, IndexError) | ||
| 1/0 | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
pR0Ps marked this conversation as resolved. Show resolvedHide resolvedUh oh!There was an error while loading.Please reload this page. | ||
| self.assertIsInstance(sys.exception().__context__, IndexError) | ||
| self.assertIsInstance(sys.exception(), IndexError) | ||
| try: | ||
| raise IndexError() | ||
| except: | ||
| try: | ||
| raise TypeError() | ||
| except: | ||
| with self.assertRaises(ZeroDivisionError): | ||
| with ctx(reraise=True): | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| self.assertIsInstance(sys.exception().__context__, IndexError) | ||
| try: | ||
| raise ValueError() | ||
| except: | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
pR0Ps marked this conversation as resolved. Show resolvedHide resolvedUh oh!There was an error while loading.Please reload this page. | ||
| self.assertIsInstance(sys.exception().__context__, TypeError) | ||
| self.assertIsInstance(sys.exception().__context__.__context__, IndexError) | ||
| 1/0 | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| self.assertIsInstance(sys.exception().__context__, IndexError) | ||
| self.assertIsInstance(sys.exception(), IndexError) | ||
| def _create_contextmanager_attribs(self): | ||
| def attribs(**kw): | ||
| def decorate(func): | ||
125 changes: 125 additions & 0 deletionsLib/test/test_sys.py
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -161,6 +161,131 @@ def f(): | ||
| self.assertIsInstance(e, ValueError) | ||
| self.assertIs(exc, e) | ||
| class SetExceptionTests(unittest.TestCase): | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others.Learn more. The suggestion is to move this from sys to contextlib. Right? | ||
| def tearDown(self): | ||
| # make sure we don't leave the global exception set | ||
| sys._set_exception(None); | ||
| def test_set_exc_invalid_values(self): | ||
| for x in (0, "1", b"2"): | ||
| with self.assertRaises(TypeError): | ||
| sys._set_exception(x); | ||
| def test_clear_exc(self): | ||
| try: | ||
| raise ValueError() | ||
| except ValueError: | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
| sys._set_exception(None) | ||
| self.assertIsNone(sys.exception()) | ||
| def test_set_exc(self): | ||
| exc = ValueError() | ||
| self.assertIsNone(sys.exception()) | ||
| sys._set_exception(exc) | ||
| self.assertIs(sys.exception(), exc) | ||
| def test_set_exc_replaced_by_new_exception_and_restored(self): | ||
| exc = ValueError() | ||
| sys._set_exception(exc) | ||
| self.assertIs(sys.exception(), exc) | ||
| try: | ||
| raise TypeError() | ||
| except TypeError: | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| self.assertIs(sys.exception().__context__, exc) | ||
| self.assertIs(sys.exception(), exc) | ||
| def test_set_exc_popped_on_exit_except(self): | ||
| exc = ValueError() | ||
| try: | ||
| raise TypeError() | ||
| except TypeError: | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| sys._set_exception(exc) | ||
| self.assertIs(sys.exception(), exc) | ||
| self.assertIsNone(sys.exception()) | ||
| def test_cleared_exc_overridden_and_restored(self): | ||
| try: | ||
| raise ValueError() | ||
| except ValueError: | ||
| try: | ||
| raise TypeError() | ||
| except TypeError: | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| sys._set_exception(None) | ||
| self.assertIsNone(sys.exception()) | ||
| try: | ||
| raise IndexError() | ||
| except IndexError: | ||
| self.assertIsInstance(sys.exception(), IndexError) | ||
| self.assertIsNone(sys.exception().__context__) | ||
| self.assertIsNone(sys.exception()) | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
| self.assertIsNone(sys.exception()) | ||
| def test_clear_exc_in_generator(self): | ||
| def inner(): | ||
| self.assertIsNone(sys.exception()) | ||
| yield | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
| sys._set_exception(None) | ||
| self.assertIsNone(sys.exception()) | ||
| yield | ||
| self.assertIsNone(sys.exception()) | ||
| # with a single exception in exc_info stack | ||
| g = inner() | ||
| next(g) | ||
| try: | ||
| raise ValueError() | ||
| except: | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
| next(g) | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
| self.assertIsNone(sys.exception()) | ||
| with self.assertRaises(StopIteration): | ||
| next(g) | ||
| self.assertIsNone(sys.exception()) | ||
| # with multiple exceptions in exc_info stack by chaining generators | ||
| def outer(): | ||
| g = inner() | ||
| self.assertIsNone(sys.exception()) | ||
| yield next(g) | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| try: | ||
| raise ValueError() | ||
| except: | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
| self.assertIsInstance(sys.exception().__context__, TypeError) | ||
| yield next(g) | ||
| # at this point the TypeError from the caller has been handled | ||
| # by the caller's except block. Even still, it should still be | ||
| # referenced as the __context__ of the current exception. | ||
| self.assertIsInstance(sys.exception(), ValueError) | ||
| self.assertIsInstance(sys.exception().__context__, TypeError) | ||
| # not handling an exception, caller isn't handling one either | ||
| self.assertIsNone(sys.exception()) | ||
| with self.assertRaises(StopIteration): | ||
| next(g) | ||
| self.assertIsNone(sys.exception()) | ||
| g = outer() | ||
| next(g) | ||
| try: | ||
| raise TypeError() | ||
| except: | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| next(g) | ||
| self.assertIsInstance(sys.exception(), TypeError) | ||
| self.assertIsNone(sys.exception()) | ||
| with self.assertRaises(StopIteration): | ||
| next(g) | ||
| self.assertIsNone(sys.exception()) | ||
| class ExceptHookTest(unittest.TestCase): | ||
2 changes: 2 additions & 0 deletionsMisc/NEWS.d/next/Core_and_Builtins/2023-12-19-17-27-08.gh-issue-111375.XeHOl_.rst
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,2 @@ | ||
| Add sys._set_exception() function that can set/clear the current exception | ||
| context. Patch by Carey Metcalfe. |
2 changes: 2 additions & 0 deletionsMisc/NEWS.d/next/Library/2023-11-03-01-44-51.gh-issue-111375.qDBcCI.rst
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,2 @@ | ||
| Fix handling of ``sys.exception()`` within ``@contextlib.contextmanager`` | ||
| functions. Patch by Carey Metcalfe. |
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