Jan 9, 2026 · Jan 9, 2026
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
    def test_custom_unraisablehook_fail(self):
        _testcapi = import_helper.import_module('_testcapi')
        from _testcapi import err_writeunraisable

        def hook_func(*args):
            raise Exception("hook_func failed")

diff --git a/Misc/NEWS.d/next/Library/2026-01-08-14-53-46.gh-issue-143547.wHBVlr.rst b/Misc/NEWS.d/next/Library/2026-01-08-14-53-46.gh-issue-143547.wHBVlr.rst
 Fix :func:`sys.unraisablehook` when the hook raises an exception and changes
 :func:`sys.unraisablehook`: hold a strong reference to the old hook. Patch
 by Victor Stinner.
diff --git a/Python/errors.c b/Python/errors.c
    _Py_EnsureTstateNotNULL(tstate);

    PyObject *err_msg = NULL;
    PyObject *hook = NULL;
    PyObject *exc_type, *exc_value, *exc_tb;
    _PyErr_Fetch(tstate, &exc_type, &exc_value, &exc_tb);

        goto error;
    }

    PyObject *hook;
    if (_PySys_GetOptionalAttr(&_Py_ID(unraisablehook), &hook) < 0) {
        Py_DECREF(hook_args);
        err_msg_str = NULL;
    }

    if (_PySys_Audit(tstate, "sys.unraisablehook", "OO", hook, hook_args) < 0) {
        Py_DECREF(hook);
        Py_DECREF(hook_args);
        err_msg_str = "Exception ignored in audit hook";
        obj = NULL;
        goto error;
    }

    if (hook == Py_None) {
        Py_DECREF(hook);
        Py_DECREF(hook_args);
        goto default_hook;
    }

    PyObject *res = PyObject_CallOneArg(hook, hook_args);
    Py_DECREF(hook);
    Py_DECREF(hook_args);
    if (res != NULL) {
        Py_DECREF(res);
    Py_XDECREF(exc_value);
    Py_XDECREF(exc_tb);
    Py_XDECREF(err_msg);
    Py_XDECREF(hook);
    _PyErr_Clear(tstate); /* Just in case */
 }
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1480,6 +1480,7 @@ def hook_func(args):
		def test_custom_unraisablehook_fail(self):
		_testcapi = import_helper.import_module('_testcapi')
		from _testcapi import err_writeunraisable

		def hook_func(*args):
		raise Exception("hook_func failed")

Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		Fix :func:`sys.unraisablehook` when the hook raises an exception and changes
		:func:`sys.unraisablehook`: hold a strong reference to the old hook. Patch
		by Victor Stinner.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1632,6 +1632,7 @@ format_unraisable_v(const char format, va_list va, PyObject obj)
		_Py_EnsureTstateNotNULL(tstate);

		PyObject *err_msg = NULL;
		PyObject *hook = NULL;
		PyObject exc_type, exc_value, *exc_tb;
		_PyErr_Fetch(tstate, &exc_type, &exc_value, &exc_tb);

Expand DownExpand Up		@@ -1676,7 +1677,6 @@ format_unraisable_v(const char format, va_list va, PyObject obj)
		goto error;
		}

		PyObject *hook;
		if (_PySys_GetOptionalAttr(&_Py_ID(unraisablehook), &hook) < 0) {
		Py_DECREF(hook_args);
		err_msg_str = NULL;
Expand All		@@ -1689,21 +1689,18 @@ format_unraisable_v(const char format, va_list va, PyObject obj)
		}

		if (_PySys_Audit(tstate, "sys.unraisablehook", "OO", hook, hook_args) < 0) {
		Py_DECREF(hook);
		Py_DECREF(hook_args);
		err_msg_str = "Exception ignored in audit hook";
		obj = NULL;
		goto error;
		}

		if (hook == Py_None) {
		Py_DECREF(hook);
		Py_DECREF(hook_args);
		goto default_hook;
		}

		PyObject *res = PyObject_CallOneArg(hook, hook_args);
		Py_DECREF(hook);
		Py_DECREF(hook_args);
		if (res != NULL) {
		Py_DECREF(res);
Expand DownExpand Up		@@ -1733,6 +1730,7 @@ format_unraisable_v(const char format, va_list va, PyObject obj)
		Py_XDECREF(exc_value);
		Py_XDECREF(exc_tb);
		Py_XDECREF(err_msg);
		Py_XDECREF(hook);
		_PyErr_Clear(tstate); /* Just in case */
		}

Expand Down