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[3.13] gh-78465: Fix error message for cls.__new__(cls, ...) where cls is not instantiable (GH-135981) #136031

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Merged
merged 1 commit into from
Jun 27, 2025
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[3.13] gh-78465: Fix error message for cls.__new__(cls, ...) where cls is not instantiable (GH-135981) #136031

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1 change: 1 addition & 0 deletions Lib/test/support/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2269,6 +2269,7 @@ def check_disallow_instantiation(testcase, tp, *args, **kwds):
qualname = f"{name}"
msg = f"cannot create '{re.escape(qualname)}' instances"
testcase.assertRaisesRegex(TypeError, msg, tp, *args, **kwds)
testcase.assertRaisesRegex(TypeError, msg, tp.__new__, tp, *args, **kwds)

def get_recursion_depth():
"""Get the recursion depth of the caller function.
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7 changes: 1 addition & 6 deletions Lib/test/test_sys.py
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Expand Up @@ -894,12 +894,7 @@ def test_sys_flags(self):
def assert_raise_on_new_sys_type(self, sys_attr):
# Users are intentionally prevented from creating new instances of
# sys.flags, sys.version_info, and sys.getwindowsversion.
arg = sys_attr
attr_type = type(sys_attr)
with self.assertRaises(TypeError):
attr_type(arg)
with self.assertRaises(TypeError):
attr_type.__new__(attr_type, arg)
support.check_disallow_instantiation(self, type(sys_attr), sys_attr)

def test_sys_flags_no_instantiation(self):
self.assert_raise_on_new_sys_type(sys.flags)
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2025-06-26-15-25-51.gh-issue-78465.MbDN8X.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix error message for ``cls.__new__(cls, ...)`` where ``cls`` is not
instantiable builtin or extension type (with ``tp_new`` set to ``NULL``).
5 changes: 5 additions & 0 deletions Objects/typeobject.c
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Expand Up @@ -9087,6 +9087,11 @@ tp_new_wrapper(PyObject *self, PyObject *args, PyObject *kwds)
/* If staticbase is NULL now, it is a really weird type.
In the spirit of backwards compatibility (?), just shut up. */
if (staticbase && staticbase->tp_new != type->tp_new) {
if (staticbase->tp_new == NULL) {
PyErr_Format(PyExc_TypeError,
"cannot create '%s' instances", subtype->tp_name);
return NULL;
}
PyErr_Format(PyExc_TypeError,
"%s.__new__(%s) is not safe, use %s.__new__()",
type->tp_name,
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