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bpo-36829: Add _PyErr_WriteUnraisableMsg() #13488

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merged 1 commit into from
May 27, 2019
Merged

bpo-36829: Add _PyErr_WriteUnraisableMsg() #13488

merged 1 commit into from
May 27, 2019

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vstinner
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@vstinner vstinner commented May 22, 2019 •
edited by bedevere-bot
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  • sys.unraisablehook: add 'err_msg' field to UnraisableHookArgs.
  • Use _PyErr_WriteUnraisableMsg() in _ctypes _DictRemover_call()
    and gc delete_garbage().

https://bugs.python.org/issue36829

@vstinner vstinner requested a review from serhiy-storchaka May 22, 2019 10:10
This was referenced May 22, 2019
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Interesting case: _PyErr_WarnUnawaitedCoroutine():

        if (PyErr_WarnFormat(PyExc_RuntimeWarning, 1,
                             "coroutine '%.50S' was never awaited",
                             ((PyCoroObject *)coro)->cr_qualname) < 0)
        {
            PyErr_WriteUnraisable(coro);
        }

The unraisable exception is logged with default "Exception ignored in: ..." message. Should we use a customized error message here?

In my PR #13490, I have to catch stderr and sys.unraisablehook to catch the warning and the unraisable exception in test_coroutines.test_unawaited_warning_when_module_broken():
https://github.com/python/cpython/pull/13490/files

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@graingert @pablogsal @serhiy-storchaka: Would you mind to review this PR? I don't recall who asked me to allow to specify a custom error message :-)

serhiy-storchaka
serhiy-storchaka reviewed May 22, 2019
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Python/errors.c
@@ -1040,6 +1053,14 @@ write_unraisable_exc_file(PyObject *exc_type, PyObject *exc_value,
return -1;
}
}
else if (err_msg != NULL && err_msg != Py_None) {
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I think you can avoid duplication of the code.

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I prefer to have a single PyFile_WriteString(":\n", file) call in this code path, rather than trying to factorize the code too much, to reduce the risk of failure in the hook.

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I rebased my PR and merged conflicts.

@vstinner
bpo-36829: Add _PyErr_WriteUnraisableMsg()
a56e060 
* sys.unraisablehook: add 'err_msg' field to UnraisableHookArgs.
* Use _PyErr_WriteUnraisableMsg() in _ctypes _DictRemover_call()
  and gc delete_garbage().
@vstinner
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@serhiy-storchaka: Would you mind to review the update PR?

serhiy-storchaka
serhiy-storchaka reviewed May 24, 2019
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Doc/library/sys.rst
* *object*: Object causing the exception, can be ``None``.

:func:`sys.unraisablehook` can be overridden to control how unraisable
exceptions are handled.

The default hook formats *err_msg* and *object* as:
``f'{err_msg}: {object!r}'``; use "Exception ignored in" error message
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Suggested change
``f'{err_msg}: {object!r}'``; use "Exception ignored in" error message
``f'Exception ignored {err_msg}: {object!r}'``; use "Exception ignored in" error message

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It really logs f'{err_msg}: {object!r}'. _PyErr_WriteUnraisableMsg("xxx") sets err_msg to "Exception ignored xxx".

pablogsal
pablogsal reviewed May 24, 2019
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Python/errors.c
@@ -1322,13 +1351,20 @@ PyErr_WriteUnraisable(PyObject *obj)
}
}

if (err_msg_str != NULL) {
err_msg = PyUnicode_FromFormat("Exception ignored %s", err_msg_str);
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Hummm, why don't allowing the caller to control the full error message? (Instead of prepending "Exception ignored")

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@serhiy-storchaka asked me to do so :-) And when I started a draft change to convert existing PyErr_WriteUnraisable() to _PyErr_WriteUnraisableMsg(), I always started error messages with "Exception ignored ".

The hook allows to control the full error message. Only proposed _PyErr_WriteUnraisableMsg() enfoce "Exception ignored " prefix. We might add a new function later if needed to let control the full error message.

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@vstinner vstinner May 26, 2019 •
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By the way, making "Exception ignored " prefix part of the API should reduce the size of the Python executable binary since constant strings are shorter (remove common "Exception ignored " prefix ;-)).

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@serhiy-storchaka @pablogsal: So do you agree each other on "Exception ignored" prefix? :-)

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pablogsal commented May 26, 2019 •
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So do you agree each other on "Exception ignored" prefix? :-)

Yup, I'm happy with it :)

@vstinner vstinner merged commit 71c52e3 into python:master May 27, 2019
@vstinner vstinner deleted the unraisable_msg branch May 27, 2019 06:57
DinoV pushed a commit to DinoV/cpython that referenced this pull request Jan 14, 2020
@vstinner @DinoV
bpo-36829: Add _PyErr_WriteUnraisableMsg() (pythonGH-13488)
c9d43b2 
* sys.unraisablehook: add 'err_msg' field to UnraisableHookArgs.
* Use _PyErr_WriteUnraisableMsg() in _ctypes _DictRemover_call()
  and gc delete_garbage().
@encukou encukou mentioned this pull request Aug 2, 2024
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