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gh-158345: Don't grow an array when append, insert or extend overflows #158348

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gh-158345: Don't grow an array when append, insert or extend overflows
fedonman Sep 28, 2026
f0fe2dc
Call setitem once in ins1() and remove the new slot if it fails
fedonman Nov 2, 2026
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20 changes: 20 additions & 0 deletions Lib/test/test_array.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1612,13 +1612,26 @@ def test_overflows(self):
self.assertRaises(OverflowError, array.array, self.typecode, [123456])
# Overflows also float type:
self.assertRaises(OverflowError, array.array, self.typecode, [1e300])
# A failed append, insert or extend leaves the array unchanged:
for x in 123456, 1e300:
a = array.array(self.typecode, [1])
self.assertRaises(OverflowError, a.append, x)
self.assertRaises(OverflowError, a.insert, 0, x)
self.assertRaises(OverflowError, a.extend, [x])
self.assertEqual(a, array.array(self.typecode, [1]))

class FloatTest(FPTest, unittest.TestCase):
typecode = 'f'
minitemsize = 4

def test_overflows(self):
self.assertRaises(OverflowError, array.array, self.typecode, [1e300])
# A failed append, insert or extend leaves the array unchanged:
a = array.array(self.typecode, [1])
self.assertRaises(OverflowError, a.append, 1e300)
self.assertRaises(OverflowError, a.insert, 0, 1e300)
self.assertRaises(OverflowError, a.extend, [1e300])
self.assertEqual(a, array.array(self.typecode, [1]))

class DoubleTest(FPTest, unittest.TestCase):
typecode = 'd'
Expand Down Expand Up @@ -1649,6 +1662,13 @@ class ComplexFloatTest(CFPTest, unittest.TestCase):
def test_overflows(self):
self.assertRaises(OverflowError, array.array, self.typecode, [1e300])
self.assertRaises(OverflowError, array.array, self.typecode, [1e300j])
# A failed append, insert or extend leaves the array unchanged:
for x in 1e300, 1e300j:
a = array.array(self.typecode, [1])
self.assertRaises(OverflowError, a.append, x)
self.assertRaises(OverflowError, a.insert, 0, x)
self.assertRaises(OverflowError, a.extend, [x])
self.assertEqual(a, array.array(self.typecode, [1]))

class ComplexDoubleTest(CFPTest, unittest.TestCase):
typecode = 'Zd'
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-09-28-13-52-36.gh-issue-158345.GNlDCF.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix :meth:`array.array.append`, :meth:`~array.array.insert` and
:meth:`~array.array.extend` leaving an extra item in the array when they
raise :exc:`OverflowError` for the ``'e'``, ``'f'`` or ``'Zf'`` type code.
10 changes: 7 additions & 3 deletions Modules/arraymodule.c
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Expand Up @@ -823,6 +823,8 @@ getarrayitem(PyObject *op, Py_ssize_t i)
return (*ap->ob_descr->getitem)(ap, i);
}

static int array_del_slice(arrayobject *a, Py_ssize_t ilow, Py_ssize_t ihigh);

static int
ins1(arrayobject *self, Py_ssize_t where, PyObject *v)
{
Expand All @@ -832,8 +834,6 @@ ins1(arrayobject *self, Py_ssize_t where, PyObject *v)
PyErr_BadInternalCall();
return -1;
}
if ((*self->ob_descr->setitem)(self, -1, v) < 0)
return -1;

if (array_resize(self, n+1) == -1)
return -1;
Expand All @@ -850,7 +850,11 @@ ins1(arrayobject *self, Py_ssize_t where, PyObject *v)
memmove(items + (where+1)*self->ob_descr->itemsize,
items + where*self->ob_descr->itemsize,
(n-where)*self->ob_descr->itemsize);
return (*self->ob_descr->setitem)(self, where, v);
if ((*self->ob_descr->setitem)(self, where, v) < 0) {
array_del_slice(self, where, where+1);
return -1;
}
return 0;
}

/* Methods */
Expand Down
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