gh-122559: Synchronize C and Python implementation of the io module a…

…bout pickling In the C implementation, remove __reduce__ and __reduce_ex__ methods that always raise TypeError and restore __getstate__ methods that always raise TypeErrori. This restores fine details of the pre-3.12 behavior and unifies both implementations.
python · serhiy-storchaka · May 4, 2025 · Aug 2, 2024 · Aug 3, 2024 · Sep 9, 2024
commit f6e66a6faf689a2f2d6ea1f65d70dafe6eaabc77
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
@@ -1336,6 +1336,28 @@ def test_readonly_attributes(self):
        with self.assertRaises(AttributeError):
            buf.raw = x

+    def test_pickling_subclass(self):
+        global MyBufferedIO
+        class MyBufferedIO(self.tp):
+            def __init__(self, raw, tag):
+                super().__init__(raw)
+                self.tag = tag
+            def __getstate__(self):
+                return self.tag, self.raw.getvalue()
+            def __setstate__(slf, state):
+                tag, value = state
+                slf.__init__(self.BytesIO(value), tag)
+
+        raw = self.BytesIO(b'data')
+        buf = MyBufferedIO(raw, tag='ham')
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            with self.subTest(protocol=proto):
+                pickled = pickle.dumps(buf, proto)
+                newbuf = pickle.loads(pickled)
+                self.assertEqual(newbuf.raw.getvalue(), b'data')
+                self.assertEqual(newbuf.tag, 'ham')
+        del MyBufferedIO
+

 class SizeofTest:

@@ -3919,6 +3941,28 @@ def test_issue35928(self):
        f.write(res)
        self.assertEqual(res + f.readline(), 'foo\nbar\n')

+    def test_pickling_subclass(self):
+        global MyTextIO
+        class MyTextIO(self.TextIOWrapper):
+            def __init__(self, raw, tag):
+                super().__init__(raw)
+                self.tag = tag
+            def __getstate__(self):
+                return self.tag, self.buffer.getvalue()
+            def __setstate__(slf, state):
+                tag, value = state
+                slf.__init__(self.BytesIO(value), tag)
+
+        raw = self.BytesIO(b'data')
+        txt = MyTextIO(raw, 'ham')
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            with self.subTest(protocol=proto):
+                pickled = pickle.dumps(txt, proto)
+                newtxt = pickle.loads(pickled)
+                self.assertEqual(newtxt.buffer.getvalue(), b'data')
+                self.assertEqual(newtxt.tag, 'ham')
+        del MyTextIO
+

 class MemviewBytesIO(io.BytesIO):
    '''A BytesIO object whose read method returns memoryviews

diff --git a/Misc/NEWS.d/next/Library/2024-08-02-20-01-36.gh-issue-122559.2JlJr3.rst b/Misc/NEWS.d/next/Library/2024-08-02-20-01-36.gh-issue-122559.2JlJr3.rst
@@ -0,0 +1,6 @@
+Remove :meth:`!__reduce__` and :meth:`!__reduce_ex__` methods that always
+raise :exc:`TypeError` in the C implementation of :class:`io.FileIO`,
+:class:`io.BufferedReader`, :class:`io.BufferedWriter` and
+:class:`io.BufferedRandom` and replace them with :meth:`!__getstatus__`
+methods that always raise :exc:`!TypeError`. This restores fine details of
+behavior of Python 3.11 and older versions.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
@@ -2530,8 +2530,7 @@ static PyMethodDef bufferedreader_methods[] = {
    _IO__BUFFERED_TRUNCATE_METHODDEF
    _IO__BUFFERED___SIZEOF___METHODDEF

-    {"__reduce__", _PyIOBase_cannot_pickle, METH_NOARGS},
-    {"__reduce_ex__", _PyIOBase_cannot_pickle, METH_O},
+    {"__getstate__", _PyIOBase_cannot_pickle, METH_NOARGS},
    {NULL, NULL}
 };

@@ -2590,8 +2589,7 @@ static PyMethodDef bufferedwriter_methods[] = {
    _IO__BUFFERED_TELL_METHODDEF
    _IO__BUFFERED___SIZEOF___METHODDEF

-    {"__reduce__", _PyIOBase_cannot_pickle, METH_NOARGS},
-    {"__reduce_ex__", _PyIOBase_cannot_pickle, METH_O},
+    {"__getstate__", _PyIOBase_cannot_pickle, METH_NOARGS},
    {NULL, NULL}
 };

@@ -2708,8 +2706,7 @@ static PyMethodDef bufferedrandom_methods[] = {
    _IO_BUFFEREDWRITER_WRITE_METHODDEF
    _IO__BUFFERED___SIZEOF___METHODDEF

-    {"__reduce__", _PyIOBase_cannot_pickle, METH_NOARGS},
-    {"__reduce_ex__", _PyIOBase_cannot_pickle, METH_O},
+    {"__getstate__", _PyIOBase_cannot_pickle, METH_NOARGS},
    {NULL, NULL}
 };


diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
@@ -1204,8 +1204,7 @@ static PyMethodDef fileio_methods[] = {
    _IO_FILEIO_FILENO_METHODDEF
    _IO_FILEIO_ISATTY_METHODDEF
    {"_dealloc_warn", (PyCFunction)fileio_dealloc_warn, METH_O, NULL},
-    {"__reduce__", _PyIOBase_cannot_pickle, METH_NOARGS},
-    {"__reduce_ex__", _PyIOBase_cannot_pickle, METH_O},
+    {"__getstate__", _PyIOBase_cannot_pickle, METH_NOARGS},
    {NULL,           NULL}             /* sentinel */
 };


diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
@@ -3350,8 +3350,7 @@ static PyMethodDef textiowrapper_methods[] = {
    _IO_TEXTIOWRAPPER_TELL_METHODDEF
    _IO_TEXTIOWRAPPER_TRUNCATE_METHODDEF

-    {"__reduce__", _PyIOBase_cannot_pickle, METH_NOARGS},
-    {"__reduce_ex__", _PyIOBase_cannot_pickle, METH_O},
+    {"__getstate__", _PyIOBase_cannot_pickle, METH_NOARGS},
    {NULL, NULL}
 };