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gh-158585: Adjust _PyBytes_FormatEx() allocation #158823

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Merged
vstinner merged 1 commit into from
Oct 5, 2026
+6 −4
Merged

gh-158585: Adjust _PyBytes_FormatEx() allocation #158823

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2 changes: 1 addition & 1 deletion Lib/test/test_bytes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -894,7 +894,7 @@ def __int__(self):
def test_memory_leak_gh_140939(self):
# gh-140939: MemoryError is raised without leaking
_testcapi = import_helper.import_module('_testcapi')
with self.assertRaises(MemoryError):
with self.assertRaises((MemoryError, OverflowError)):
b = self.type2test(b'%*b')
b % (_testcapi.PY_SSIZE_T_MAX, b'abc')

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8 changes: 5 additions & 3 deletions Objects/bytesobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -747,6 +747,7 @@ _PyBytes_FormatEx(const char *format, Py_ssize_t format_len,
char onechar; /* For byte_converter() */
Py_ssize_t alloc;

const char *start = fmt;
fmt++;
if (*fmt == '%') {
*res++ = '%';
Expand Down Expand Up @@ -1108,9 +1109,10 @@ _PyBytes_FormatEx(const char *format, Py_ssize_t format_len,
alloc = width;
if (sign != 0 && len == width)
alloc++;
/* 2: size preallocated for %s */
if (alloc > 2) {
res = PyBytesWriter_GrowAndUpdatePointer(writer, alloc - 2, res);
/* size preallocated for the format */
Py_ssize_t prealloc = fmt - start;
if (alloc > prealloc) {
res = PyBytesWriter_GrowAndUpdatePointer(writer, alloc - prealloc, res);
if (res == NULL) {
Py_XDECREF(temp);
goto error;
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