https://github.com/python/cpython/commit/182f3231542e84fd1b0c795898f69f61fe35df0e
commit: 182f3231542e84fd1b0c795898f69f61fe35df0e
branch: main
author: Victor Stinner <[email protected]>
committer: vstinner <[email protected]>
date: 2026-10-05T03:09:25Z
summary:
gh-158585: Adjust _PyBytes_FormatEx() allocation (#158823)
Count properly the number of preallocated bytes when growing the
buffer.
files:
M Lib/test/test_bytes.py
M Objects/bytesobject.c
diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index f87a924c57016e..96190a7f582170 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -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')
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index 9bd9afc9b51ba4..1917055d25198f 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -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++ = '%';
@@ -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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