python · inventshah · Oct 27, 2025 · Oct 27, 2025 · Oct 27, 2025 · Oct 27, 2025
diff --git a/Lib/test/test_io/test_bufferedio.py b/Lib/test/test_io/test_bufferedio.py
@@ -962,6 +962,16 @@ def test_args_error(self):
         with self.assertRaisesRegex(TypeError, "BufferedWriter"):
             self.tp(self.BytesIO(), 1024, 1024, 1024)
 
+    def test_closed_errors(self):
+        # gh-140650: check TypeError is raised
+        class MockRawIOWithoutClosed(self.MockRawIO):
+            closed = NotImplemented
+
+        bufio = self.tp(MockRawIOWithoutClosed())
+        self.assertRaises(TypeError, bufio.write, b"")
+        self.assertRaises(TypeError, bufio.flush)
+        self.assertRaises(TypeError, bufio.close)
+
 
 class PyBufferedWriterTest(BufferedWriterTest, PyTestCase):
     tp = pyio.BufferedWriter

diff --git a/Misc/NEWS.d/next/Library/2025-10-27-00-40-49.gh-issue-140650.DYJPJ9.rst b/Misc/NEWS.d/next/Library/2025-10-27-00-40-49.gh-issue-140650.DYJPJ9.rst
@@ -0,0 +1,2 @@
+Fix an issue where closing :class:`io.BufferedWriter` could crash
+if the closed attribute raised an exception.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
@@ -362,16 +362,24 @@ _enter_buffered_busy(buffered *self)
     }
 
 #define IS_CLOSED(self) \
-    (!self->buffer || \
+    (!self->buffer ? 1 : \
     (self->fast_closed_checks \
      ? _PyFileIO_closed(self->raw) \
      : buffered_closed(self)))
 
 #define CHECK_CLOSED(self, error_msg) \
-    if (IS_CLOSED(self) && (Py_SAFE_DOWNCAST(READAHEAD(self), Py_off_t, Py_ssize_t) == 0)) { \
-        PyErr_SetString(PyExc_ValueError, error_msg); \
-        return NULL; \
-    } \
+    do { \
+        int _closed = IS_CLOSED(self); \
+        if (_closed < 0) { \
+            return NULL; \
+        } \
+        if (_closed && \
+            (Py_SAFE_DOWNCAST(READAHEAD(self), Py_off_t, Py_ssize_t) == 0)) \
+        { \
+            PyErr_SetString(PyExc_ValueError, error_msg); \
+            return NULL; \
+        } \
+    } while (0);
 
 #define VALID_READ_BUFFER(self) \
     (self->readable && self->read_end != -1)
@@ -555,10 +563,11 @@ _io__Buffered_close_impl(buffered *self)
     }
     /* gh-138720: Use IS_CLOSED to match flush CHECK_CLOSED. */
     r = IS_CLOSED(self);
-    if (r < 0)
+    if (r < 0) {
         goto end;
+    }
     if (r > 0) {
-        res = Py_NewRef(Py_None);
+        res = Py_None;
         goto end;
     }
 
@@ -2079,6 +2088,7 @@ _io_BufferedWriter_write_impl(buffered *self, Py_buffer *buffer)
     PyObject *res = NULL;
     Py_ssize_t written, avail, remaining;
     Py_off_t offset;
+    int r;
 
     CHECK_INITIALIZED(self)
 
@@ -2087,7 +2097,11 @@ _io_BufferedWriter_write_impl(buffered *self, Py_buffer *buffer)
 
     /* Issue #31976: Check for closed file after acquiring the lock. Another
        thread could be holding the lock while closing the file. */
-    if (IS_CLOSED(self)) {
+    r = IS_CLOSED(self);
+    if (r < 0) {
+        goto error;
+    }
+    if (r > 0) {
         PyErr_SetString(PyExc_ValueError, "write to closed file");
         goto error;
     }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Fix an issue where closing :class:`io.BufferedWriter` could crash
		if the closed attribute raised an exception.
Copy link Member serhiy-storchaka Oct 29, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. This is not accurate. Bad things happen when the value of the `closed` attribute cannot be converted to boolean. Copy link Contributor Author inventshah Oct 29, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. In addition to the "cannot be converted to a boolean" case, this patch also fixes cases where `closed` is defined as a managed attribute equivalent to @property def closed(self): raise Exception() Should the news entry just focus on the first type error case, or mention fixing this case as well? Copy link Member efimov-mikhail Oct 29, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Maybe we should add tests on this behavior too? Copy link Contributor Author inventshah Oct 30, 2025 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Updated the news to reflect both cases, and added a test for the other behavior. I wonder if we need a line mentioning that exceptions from `.closed` are no longer swallowed by the corresponding methods (like .`write()`, `.flush()`)