gh-122559: Synchronize C and Python implementation of the io module about pickling (GH-122628)

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.

Author: serhiy-storchaka

Lib/test/test_io.py

@@ -1373,6 +1373,28 @@ 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:
 
@@ -3950,6 +3972,28 @@ 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
+
     @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
     def test_read_non_blocking(self):
         import os

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 default
+:meth:`!__getstate__` methods that raise :exc:`!TypeError`.
+This restores fine details of behavior of Python 3.11 and older versions.

Modules/_io/bufferedio.c

@@ -2555,8 +2555,7 @@ 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}
 };
 
@@ -2615,8 +2614,7 @@ 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}
 };
 
@@ -2733,8 +2731,7 @@ 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}
 };
 

Modules/_io/fileio.c

@@ -1262,8 +1262,7 @@ static PyMethodDef fileio_methods[] = {
     _IO_FILEIO_ISATTY_METHODDEF
     {"_isatty_open_only", _io_FileIO_isatty_open_only, METH_NOARGS},
     {"_dealloc_warn", 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 */
 };
 

Modules/_io/textio.c

@@ -3366,8 +3366,7 @@ 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}
 };