Sync pre-release CPython main branch from GitHub (2026-08-08)

Summary:
Imported python/cpython `3.16.0a0` from upstream rev [`998b890`](https://www.github.com/python/cpython/commit/998b89020456db591be41e6529b04f4bc8c8181f) (committed 2026-08-08 15:11:23+00:00).

# Commit Info

- Base: (`3.16.0a0`) - [`8ed1479`](https://www.github.com/python/cpython/commit/8ed1479619a3487af72a7c44bf61c9711370d4da) (commit date: 2026-08-08 01:42:23+00:00)
- Imported: (`3.16.0a0`) - [`998b890`](https://www.github.com/python/cpython/commit/998b89020456db591be41e6529b04f4bc8c8181f) (commit date: 2026-08-08 15:11:23+00:00)

# Noteworthy file changes

- Low-signal files (1 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GOf0tS00AVBSZw0IAJdT_nZo3IRxbr0LAAAz

Differential Revision: D115339937

fbshipit-source-id: c25a95535c19e6a8fd81f4bab56536b99295e39d

Author: generatedunixname1734921407115435

Lib/_pyio.py

@@ -921,7 +921,7 @@ def getbuffer(self):
 
     def close(self):
         if self._buffer is not None:
-            self._buffer.clear()
+            self._buffer = bytearray()
         super().close()
 
     def read(self, size=-1):

Lib/test/test_io/test_memoryio.py

@@ -457,7 +457,9 @@ def test_getbuffer(self):
         # raises a BufferError.
         self.assertRaises(BufferError, memio.write, b'x' * 100)
         self.assertRaises(BufferError, memio.truncate)
-        self.assertRaises(BufferError, memio.close)
+        # gh-111049: _io.BytesIO detach on close would lead to corruption.
+        if self.ioclass is io.BytesIO:
+            self.assertRaises(BufferError, memio.close)
         self.assertFalse(memio.closed)
         # Mutating the buffer updates the BytesIO
         buf[3:6] = b"abc"
@@ -471,6 +473,23 @@ def test_getbuffer(self):
         memio.close()
         self.assertRaises(ValueError, memio.getbuffer)
 
+    def test_getbuffer_delete(self):
+        # gh-111330: _pyio .close() works and the buffer stays working
+        if self.ioclass is io.BytesIO:
+            # gh-111049: _io.BytesIO detach on close would lead to corruption.
+            # gh-111331: It would be nice to support this.
+            self.skipTest("io.BytesIO does not support, gh-111049")
+
+        memio = self.ioclass(b"1234567890")
+        buf = memio.getbuffer()
+        self.assertEqual(bytes(buf), b"1234567890")
+        memio.close()
+        self.assertTrue(memio.closed)
+        self.assertEqual(bytes(buf), b"1234567890")
+        buf[3:6] = b"abc"
+        self.assertEqual(bytes(buf), b"123abc7890")
+        self.assertRaises(ValueError, memio.getbuffer)
+
     def test_getbuffer_empty(self):
         memio = self.ioclass()
         buf = memio.getbuffer()
@@ -493,9 +512,11 @@ def test_getbuffer_gc_collect(self):
         # Create a reference loop.
         a = [buf]
         a.append(a)
-        # The Python implementation emits an unraisable exception.
-        with support.catch_unraisable_exception():
+
+        # gh-111330: _pyio GC with exports should pass.
+        with support.catch_unraisable_exception() as cm:
             del memio
+            self.assertIsNone(cm.unraisable)
         del buf
         del a
         # The C implementation emits an unraisable exception.

Misc/NEWS.d/next/Library/2026-06-26-13-00-46.gh-issue-111330.DBcCXA.rst

@@ -0,0 +1,2 @@
+Update pure-Python :class:`io.BytesIO` to close cleanly when the data has an
+export such as a :class:`memoryview`.