preserve sign of IS_CLOSED(...)

Author: inventshah

Lib/test/test_io/test_bufferedio.py

@@ -922,6 +922,14 @@ def test_slow_close_from_thread(self):
         self.assertTrue(bufio.closed)
         t.join()
 
+    def test_close_without_closed(self):
+        # gh-140650: check TypeError is raised
+        class MockRawIOWithoutClosed(self.MockRawIO):
+            closed = NotImplemented
+
+        bufio = self.tp(MockRawIOWithoutClosed())
+        self.assertRaises(TypeError, bufio.close)
+
 
 class CBufferedWriterTest(BufferedWriterTest, SizeofTest, CTestCase):
     tp = io.BufferedWriter

Misc/NEWS.d/next/Library/2025-10-27-00-40-49.gh-issue-140650.DYJPJ9.rst

@@ -0,0 +1,2 @@
+Fix an issue where :meth:`io.BufferedWriter.close` would crash when "closed"
+was not implemented.

Modules/_io/bufferedio.c

@@ -362,7 +362,7 @@ _enter_buffered_busy(buffered *self)
     }
 
 #define IS_CLOSED(self) \
-    (!self->buffer || \
+    (!self->buffer ?: \
     (self->fast_closed_checks \
      ? _PyFileIO_closed(self->raw) \
      : buffered_closed(self)))