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GeezerVison is showing github.com — bpo-36829: Add test.support.catch_unraisable_exception() by vstinner · Pull Request #13490 · python/cpython

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@vstinner

@vstinner vstinner commented May 22, 2019 •
edited by bedevere-bot
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  • Copy test_exceptions.test_unraisable() to
    test_sys.UnraisableHookTest().
  • test_exceptions.test_unraisable() uses catch_unraisable_exception();
    simplify the test. test_sys now checks the exact output.
  • Use catch_unraisable_exception() in test_coroutines,
    test_exceptions, test_generators.

https://bugs.python.org/issue36829

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@vstinner
bpo-36829: Add test.support.catch_unraisable_exception()
1fc116b 
* Copy test_exceptions.test_unraisable() to
  test_sys.UnraisableHookTest().
* test_exceptions.test_unraisable() uses catch_unraisable_exception();
  simplify the test. test_sys now checks the exact output.
* Use catch_unraisable_exception() in test_coroutines,
  test_exceptions, test_generators.
@the-knights-who-say-ni the-knights-who-say-ni added the CLA signed label May 22, 2019
@bedevere-bot bedevere-bot added the awaiting core review label May 22, 2019
@vstinner vstinner mentioned this pull request May 22, 2019
bpo-36829: Add sys.unraisablehook() #13187
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@vstinner

vstinner commented May 22, 2019

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I chose to leave test_io unchanged on purpose: I have a local branch which fix also https://bugs.python.org/issue36918 in Lib/_pyio.py and use this new catch_unraisable_exception() function. Once this PR will be merged, I will write a second PR based on it.
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vstinner
vstinner commented May 22, 2019
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Comment thread Lib/test/test_coroutines.py

self.assertEqual(repr(cm.unraisable.object), coro_repr)
self.assertEqual(cm.unraisable.exc_type, ZeroDivisionError)
self.assertIn("was never awaited", stream.getvalue())

@vstinner vstinner May 22, 2019

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It's a little bit strange to have to catch half of the error message from stderr, and the other half from sys.unraisablehook. My PR #13488 will allow to inject the error message in the unraisable exception to catch both at the same time.

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@vstinner vstinner mentioned this pull request May 22, 2019
bpo-36829: Add _PyErr_WriteUnraisableMsg() #13488
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graingert
graingert reviewed May 22, 2019
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Comment thread Lib/test/support/__init__.py Outdated

# check the expected unraisable exception
...
finally:

@graingert graingert May 22, 2019 •
edited
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this try/with/finally is somewhat tricky, how about:

try:
    with support.throw_unraisable_exceptions():
        ...
except Exception as e:
    ... # the exception is now here

eg:

@contextlib.contextmanager
def throw_unraisable_exceptions():
    unraisable = None
    old_hook = sys.unraisablehook

    def hook(exc):
        nonlocal unraisable
        unraisable = exc

    sys.unraisablehook = hook
    try:
        yield
        if unraisable is not None:
            raise unraisable
    finally:
        unraisable = None
        sys.unraisablehook = old_hook

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@graingert graingert May 22, 2019 •
edited
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or recommend usage like this:

    with support.catch_unraisable_exceptions() as cm:
        ...
        cm.unraisable  # only available here
    assert cm.unraisable is None  # now it's gone

by updating __exit__:

   def __exit__(self, *exc_info):
        self.unraisable = None  # clear unraisable here
        sys.unraisablehook = self._old_hook

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@vstinner vstinner May 22, 2019

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Good idea :-) I implemented your __exit__ idea to avoid the need for try/finally.

throw_unraisable_exceptions() might be useful, but modified tests needs to access the 'obj' attribute of the unraisable hook. Later, they might also want to get access to the 'err_msg' attribute: #13488

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@graingert graingert May 22, 2019

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There's still a sharp edge here:

how about making cm.unraisable throw if accessed outside the context instead of being None, eg:

def __exit__(self, *exc_info):
    del self.unraisable
    sys.unraisablehook = self._old_hook

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@graingert graingert May 22, 2019 •
edited
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and if you want to access additional unraisablehook info using throw_unraisable_exceptions:

class UnraisableException(Exception):
    def __init__(self, unraisable):
        self.unraisable = unraisable
        super().__init__(self, unraisable)


@contextlib.contextmanager
def throw_unraisable_exceptions():
    unraisable = None
    old_hook = sys.unraisablehook

    def hook(unraisable_):
        nonlocal unraisable
        unraisable = unraisable_

    sys.unraisablehook = hook
    try:
        yield
        if unraisable is not None:
            raise UnraisableException(unraisable) from unraisable.exc_value
    finally:
        sys.unraisablehook = old_hook

then you can use it with:

try:
    with throw_unraisable_exceptions():
        ...
except UnraisableException as e:
    print(repr(e.__cause__))
    err_msg = e.unraisable.err_msg

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@vstinner vstinner May 24, 2019

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I wrote PR #13554 to implement your "del self.unraisable" idea.

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vstinner added 2 commits May 22, 2019 18:28
@vstinner
catch_unraisable_exception.__exit__ clears unraisable
1ffe98d 
Avoid the need for try/finally: __exit__ clears unraisable to break
the reference cycle.
@vstinner
Cleanup
5c1bf39
@vstinner
vstinner merged commit e4d300e into python:master May 22, 2019
@vstinner
vstinner deleted the catch_unraisable_exception branch May 22, 2019 21:44
@bedevere-bot bedevere-bot removed the awaiting core review label May 22, 2019
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@vstinner @graingert @the-knights-who-say-ni @bedevere-bot
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