May 17, 2025 · May 17, 2025 · May 17, 2025 · May 17, 2025 · May 17, 2025 · May 17, 2025
diff --git a/Lib/test/test_string/test_templatelib.py b/Lib/test/test_string/test_templatelib.py
        self.assertEqual(res[1].format_spec, '')
        self.assertEqual(res[2], ' yz')

    def test_exhausted(self):
        # See https://github.com/python/cpython/issues/134119.
        template_iter = iter(t"{1}")
        self.assertIsInstance(next(template_iter), Interpolation)
        self.assertRaises(StopIteration, next, template_iter)
        self.assertRaises(StopIteration, next, template_iter)


 if __name__ == '__main__':
    unittest.main()
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-05-16-20-59-12.gh-issue-134119.w8expI.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-16-20-59-12.gh-issue-134119.w8expI.rst
 Fix crash when calling :func:`next` on an exhausted template string iterator.
 Patch by Jelle Zijlstra.
diff --git a/Objects/templateobject.c b/Objects/templateobject.c
    if (self->from_strings) {
        item = PyIter_Next(self->stringsiter);
        self->from_strings = 0;
        if (item == NULL) {
            return NULL;
        }
        if (PyUnicode_GET_LENGTH(item) == 0) {
            Py_SETREF(item, PyIter_Next(self->interpolationsiter));
            self->from_strings = 1;
Original file line number	Diff line number	Diff line change
Expand Up		@@ -148,6 +148,13 @@ def test_iter(self):
		self.assertEqual(res[1].format_spec, '')
		self.assertEqual(res[2], ' yz')

		def test_exhausted(self):
		# See https://github.com/python/cpython/issues/134119.
		template_iter = iter(t"{1}")
		self.assertIsInstance(next(template_iter), Interpolation)
		self.assertRaises(StopIteration, next, template_iter)
		self.assertRaises(StopIteration, next, template_iter)


		if __name__ == '__main__':
		unittest.main()
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Fix crash when calling :func:`next` on an exhausted template string iterator.
		Patch by Jelle Zijlstra.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -23,6 +23,9 @@ templateiter_next(PyObject *op)
		if (self->from_strings) {
		item = PyIter_Next(self->stringsiter);
		self->from_strings = 0;
		if (item == NULL) {
		return NULL;
		}
		if (PyUnicode_GET_LENGTH(item) == 0) {
Copy link Contributor sergey-miryanovMay 17, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. Maybe it is worth to add condition here like `if (!item \|\| PyUnicode_GET_LENGTH(item) == 0) { Py_XSETREF(item, PyItem_Next(self->interpolationsiter)); self->from_strings = 1;}` Copy link MemberAuthor JelleZijlstraMay 17, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. I think that would potentially make an API call with an exception set, which is not allowed, right? Copy link Contributor sergey-miryanovMay 17, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. Yeah, good point. Thanks!
		Py_SETREF(item, PyIter_Next(self->interpolationsiter));
Copy link Contributor devdanzinMay 17, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. Should the result of`PyIter_Next(self->interpolationsiter)` be checked for`NULL` too? Copy link Contributor davepeckMay 17, 2025• edited Loading Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. That case just falls through to returning`NULL` safely, so it's probably fine as-is. (The fall-through is intentional: since there is always one more`string` than`interpolation`, the first`NULL` returned by the iterator will always be here.) devdanzin, lysnikolaou, and sergey-miryanov reacted with thumbs up emoji Copy link MemberAuthor JelleZijlstraMay 17, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. `Py_SETREF` is safe if it assigns to NULL, the behavior should be correct in that case.
		self->from_strings = 1;
Expand Down