bpo-36829: Add _PyErr_WriteUnraisableMsg() by vstinner · Pull Request #13488 · python/cpython (original) (raw)

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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

This was referenced

May 22, 2019

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

@@ -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.

I rebased my PR and merged conflicts.

sys.unraisablehook: add 'err_msg' field to UnraisableHookArgs.
Use _PyErr_WriteUnraisableMsg() in _ctypes _DictRemover_call() and gc delete_garbage().

* 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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``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".

@@ -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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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 ;-)).

So do you agree each other on "Exception ignored" prefix? :-)

Yup, I'm happy with it :)

DinoV pushed a commit to DinoV/cpython that referenced this pull request

Jan 14, 2020

sys.unraisablehook: add 'err_msg' field to UnraisableHookArgs.
Use _PyErr_WriteUnraisableMsg() in _ctypes _DictRemover_call() and gc delete_garbage().