gh-111330: Fix Gc of _pyio.BytesIO with exports

Swap out the buffer rather than using `.clear()` which will raise an
exception if there are epxorts.

Author: cmaloney

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

@@ -493,9 +493,11 @@ 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`.