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[3.9] bpo-42924: Fix incorrect copy in bytearray_repeat (GH-24208) #24211

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Merged
merged 1 commit into from
Apr 26, 2021
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[3.9] bpo-42924: Fix incorrect copy in bytearray_repeat (GH-24208) #24211

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10 changes: 10 additions & 0 deletions Lib/test/test_bytes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1664,6 +1664,16 @@ def test_iterator_length_hint(self):
# Shouldn't raise an error
self.assertEqual(list(it), [])

def test_repeat_after_setslice(self):
# bpo-42924: * used to copy from the wrong memory location
b = bytearray(b'abc')
b[:2] = b'x'
b1 = b * 1
b3 = b * 3
self.assertEqual(b1, b'xc')
self.assertEqual(b1, b)
self.assertEqual(b3, b'xcxcxc')


class AssortedBytesTest(unittest.TestCase):
#
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-01-13-14-06-01.bpo-42924._WS1Ok.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix ``bytearray`` repetition incorrectly copying data from the start of the buffer, even if the data is offset within the buffer (e.g. after reassigning a slice at the start of the ``bytearray`` to a shorter byte string).
6 changes: 4 additions & 2 deletions Objects/bytearrayobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -329,6 +329,7 @@ bytearray_repeat(PyByteArrayObject *self, Py_ssize_t count)
PyByteArrayObject *result;
Py_ssize_t mysize;
Py_ssize_t size;
const char *buf;

if (count < 0)
count = 0;
Expand All @@ -337,13 +338,14 @@ bytearray_repeat(PyByteArrayObject *self, Py_ssize_t count)
return PyErr_NoMemory();
size = mysize * count;
result = (PyByteArrayObject *)PyByteArray_FromStringAndSize(NULL, size);
buf = PyByteArray_AS_STRING(self);
if (result != NULL && size != 0) {
if (mysize == 1)
memset(result->ob_bytes, self->ob_bytes[0], size);
memset(result->ob_bytes, buf[0], size);
else {
Py_ssize_t i;
for (i = 0; i < count; i++)
memcpy(result->ob_bytes + i*mysize, self->ob_bytes, mysize);
memcpy(result->ob_bytes + i*mysize, buf, mysize);
}
}
return (PyObject *)result;
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