Call sys.unraisablehook in the REPL when sys.excepthook is broken

[Julian]

BPO	43148
Nosy	@vstinner, @cfbolz, @Julian, @Julian

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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assignee = None
closed_at = None
created_at = <Date 2021-02-06.20:55:56.550>
labels = ['3.10']
title = 'Call sys.unraisablehook in the REPL when sys.excepthook is broken'
updated_at = <Date 2021-02-15.16:58:07.957>
user = 'https://github.com/Julian'

bugs.python.org fields:

activity = <Date 2021-02-15.16:58:07.957>
actor = 'Julian2'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-02-06.20:55:56.550>
creator = 'Julian'
dependencies = []
files = []
hgrepos = []
issue_num = 43148
keywords = []
message_count = 3.0
messages = ['386569', '386703', '387026']
nosy_count = 4.0
nosy_names = ['vstinner', 'Carl.Friedrich.Bolz', 'Julian', 'Julian2']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue43148'
versions = ['Python 3.10']

[Julian]

At the REPL, when sys.excepthook is broken (below by setting it to a non-callable), one sees:

⊙  python3.9                                                                                                                                                                        julian@Airm
Python 3.9.1 (default, Feb  2 2021, 22:54:59) 
[Clang 12.0.0 (clang-1200.0.32.29)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys; sys.excepthook = object(); asdf
Error in sys.excepthook:
TypeError: 'object' object is not callable

Original exception was:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'asdf' is not defined

The implementation (

cpython/Python/pythonrun.c

Lines 805 to 817 in 5f18c22

	PySys_WriteStderr("Error in sys.excepthook:\n");
	PyErr_Display(exception2, v2, tb2);
	PySys_WriteStderr("\nOriginal exception was:\n");
	PyErr_Display(exception, v, tb);
	Py_DECREF(exception2);
	Py_DECREF(v2);
	Py_XDECREF(tb2);
	}
	Py_XDECREF(result);
	}
	else {
	PySys_WriteStderr("sys.excepthook is missing\n");
	PyErr_Display(exception, v, tb);

) seems to do so by reimplementing something like 3.8+'s sys.unraisablehook (well, technically it predates sys.unraisablehook by quite a while).

Seems like now that it exists, that code should now call sys.unraisablehook.

[vstinner]

It makes sense to call _PyErr_WriteUnraisableMsg() when sys.excepthook raise a new exception. Do you want to propose a PR for that?

sys.excepthook documentation mentions sys.unraisablehook:
https://docs.python.org/dev/library/sys.html#sys.excepthook

threading._make_invoke_excepthook logs threading.excepthook failure using sys.excepthook.

Note: Carl also suggested to add a way to invoke sys.unraisablehook explicitly, not only for testing purpose. It would help in some cases.

[Julian]

Thanks Victor. Yes likely happy to send a PR (have to clear a few things
off the yak stack first)

On Tue, Feb 9, 2021 at 5:38 AM STINNER Victor <report@bugs.python.org>
wrote:

STINNER Victor <vstinner@python.org> added the comment:

It makes sense to call _PyErr_WriteUnraisableMsg() when sys.excepthook
raise a new exception. Do you want to propose a PR for that?

sys.excepthook documentation mentions sys.unraisablehook:
https://docs.python.org/dev/library/sys.html#sys.excepthook

threading._make_invoke_excepthook logs threading.excepthook failure using
sys.excepthook.

Note: Carl also suggested to add a way to invoke sys.unraisablehook
explicitly, not only for testing purpose. It would help in some cases.

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<https://bugs.python.org/issue43148\>

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