https://github.com/python/cpython/commit/23eda007f8d543495ba4935df75d243d76f9ef7f
commit: 23eda007f8d543495ba4935df75d243d76f9ef7f
branch: main
author: Victor Stinner <[email protected]>
committer: vstinner <[email protected]>
date: 2026-09-12T19:06:19+02:00
summary:
gh-157242: Do not close io.BytesIO on MemoryError (#157344)
Replace _PyBytes_Resize() with _PyBytes_ResizeKeepOnError().
Fix truncate(): on error, restore string_size to its previous value.
files:
A Misc/NEWS.d/next/Library/2026-09-12-03-14-57.gh-issue-157242.ycbtjC.rst
M Lib/test/test_io/test_memoryio.py
M Modules/_io/bytesio.c
diff --git a/Lib/test/test_io/test_memoryio.py
b/Lib/test/test_io/test_memoryio.py
index 624fd78327cae10..423b99779bc6e78 100644
--- a/Lib/test/test_io/test_memoryio.py
+++ b/Lib/test/test_io/test_memoryio.py
@@ -5,6 +5,7 @@
import unittest
from test import support
+from test.support import import_helper
import gc
import io
@@ -753,6 +754,35 @@ def __buffer__(self, flags):
self.assertEqual(memio.getvalue(), b"01AAA56789")
self.assertEqual(memio.tell(), 5)
+ def test_memory_error(self):
+ # gh-157242: io.BytesIO() must not close the file on MemoryError
+ _testcapi = import_helper.import_module('_testcapi')
+
+ # write()
+ stream = self.ioclass()
+ stream.write(self.buftype('abc'))
+ with self.assertRaises(MemoryError):
+ try:
+ data = self.buftype('def')
+ _testcapi.set_nomemory(0)
+ stream.write(data)
+ finally:
+ _testcapi.remove_mem_hooks()
+ stream.write(self.buftype('123'))
+ self.assertEqual(stream.getvalue(), self.buftype('abc123'))
+
+ # truncate()
+ data = self.buftype('x' * 100)
+ stream = self.ioclass()
+ stream.write(data)
+ with self.assertRaises(MemoryError):
+ try:
+ _testcapi.set_nomemory(0)
+ stream.truncate(5)
+ finally:
+ _testcapi.remove_mem_hooks()
+ self.assertEqual(stream.getvalue(), data)
+
class TextIOTestMixin:
diff --git
a/Misc/NEWS.d/next/Library/2026-09-12-03-14-57.gh-issue-157242.ycbtjC.rst
b/Misc/NEWS.d/next/Library/2026-09-12-03-14-57.gh-issue-157242.ycbtjC.rst
new file mode 100644
index 000000000000000..54ada2892f76fac
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-09-12-03-14-57.gh-issue-157242.ycbtjC.rst
@@ -0,0 +1,2 @@
+:class:`io.BytesIO` is no longer closed on ``write()`` and ``truncate()``
+failure (:exc:`MemoryError`). Patch by Victor Stinner.
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index ab54df8c76758f9..b487d6d7beca93f 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -1,4 +1,5 @@
#include "Python.h"
+#include "pycore_bytesobject.h" // _PyBytes_ResizeKeepOnError()
#include "pycore_critical_section.h" // Py_BEGIN_CRITICAL_SECTION()
#include "pycore_object.h"
#include "pycore_pyatomic_ft_wrappers.h"
@@ -108,7 +109,7 @@ resize_unshared_buffer_lock_held(bytesio *self, Py_ssize_t
size)
Callers must detach first. */
assert(!self->buf_shared);
#endif
- int ret = _PyBytes_Resize(&self->buf, size);
+ int ret = _PyBytes_ResizeKeepOnError(&self->buf, size);
if (ret == 0) {
clear_shared_buf(self);
}
@@ -758,9 +759,12 @@ _io_BytesIO_truncate_impl(bytesio *self, PyObject *size)
}
if (new_size < self->string_size) {
+ Py_ssize_t old_string_size = self->string_size;
self->string_size = new_size;
- if (resize_buffer_lock_held(self, new_size) < 0)
+ if (resize_buffer_lock_held(self, new_size) < 0) {
+ self->string_size = old_string_size;
return NULL;
+ }
}
return PyLong_FromSsize_t(new_size);
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