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gh-160781: Only test BytesIO write overflow on the C implementation #160903

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Merged
StanFromIreland merged 1 commit into from
Oct 29, 2026
Merged

gh-160781: Only test BytesIO write overflow on the C implementation #160903

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13 changes: 9 additions & 4 deletions Lib/test/test_io/test_memoryio.py
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Original file line number Diff line number Diff line change
Expand Up @@ -591,10 +591,6 @@ def test_issue141311(self):
self.assertEqual(sys.maxsize, memio.seek(sys.maxsize))
buf = bytearray(2)
self.assertEqual(0, memio.readinto(buf))
# Writing there must not overflow the buffer size.
memio.seek(sys.maxsize - 1)
self.assertRaises((MemoryError, OverflowError), memio.write, b"x")
self.assertEqual(memio.getvalue(), b"")

def test_peek(self):
buf = self.buftype("1234567890")
Expand Down Expand Up @@ -994,6 +990,15 @@ def __index__(self):
self.assertEqual(stream.truncate(2**31), 2**31)
self.assertEqual(stream.getvalue(), b'abc')

def test_write_overflow(self):
# gh-160781: overallocation at a position near sys.maxsize
# must raise OverflowError, not SystemError.
memio = self.ioclass()
memio.seek(sys.maxsize - 1)
self.assertRaises(OverflowError, memio.write, b"x")
self.assertEqual(memio.getvalue(), b"")
self.assertEqual(memio.tell(), sys.maxsize - 1)

def test_readinto_overlapping_buffer(self):
with self.ioclass(b'abcd') as stream:
with stream.getbuffer()[1:] as target:
Expand Down
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