gh-93627: Align Python implementation of pickle with C implementation of pickle

Lib/pickle.py

@@ -396,6 +396,8 @@ def decode_long(data):
     return int.from_bytes(data, byteorder='little', signed=True)
 
 
+_NoValue = object()
+
 # Pickling machinery
 
 class _Pickler:
@@ -542,8 +544,8 @@ def save(self, obj, save_persistent_id=True):
             return
 
         rv = NotImplemented
-        reduce = getattr(self, "reducer_override", None)
-        if reduce is not None:
+        reduce = getattr(self, "reducer_override", _NoValue)
+        if reduce is not _NoValue:
             rv = reduce(obj)
 
         if rv is NotImplemented:
@@ -556,8 +558,8 @@ def save(self, obj, save_persistent_id=True):
 
             # Check private dispatch table if any, or else
             # copyreg.dispatch_table
-            reduce = getattr(self, 'dispatch_table', dispatch_table).get(t)
-            if reduce is not None:
+            reduce = getattr(self, 'dispatch_table', dispatch_table).get(t, _NoValue)
+            if reduce is not _NoValue:
                 rv = reduce(obj)
             else:
                 # Check for a class with a custom metaclass; treat as regular
@@ -567,12 +569,12 @@ def save(self, obj, save_persistent_id=True):
                     return
 
                 # Check for a __reduce_ex__ method, fall back to __reduce__
-                reduce = getattr(obj, "__reduce_ex__", None)
-                if reduce is not None:
+                reduce = getattr(obj, "__reduce_ex__", _NoValue)
+                if reduce is not _NoValue:
                     rv = reduce(self.proto)
                 else:
-                    reduce = getattr(obj, "__reduce__", None)
-                    if reduce is not None:
+                    reduce = getattr(obj, "__reduce__", _NoValue)
+                    if reduce is not _NoValue:
                         rv = reduce()
                     else:
                         raise PicklingError("Can't pickle %r object: %r" %
@@ -1705,8 +1707,8 @@ def load_build(self):
         stack = self.stack
         state = stack.pop()
         inst = stack[-1]
-        setstate = getattr(inst, "__setstate__", None)
-        if setstate is not None:
+        setstate = getattr(inst, "__setstate__", _NoValue)
+        if setstate is not _NoValue:
             setstate(state)
             return
         slotstate = None

Lib/test/test_pickle.py

@@ -570,6 +570,87 @@ def test_multiprocessing_exceptions(self):
                                  ('multiprocessing.context', name))
 
 
+class C_with_reduce_ex:
+    def __reduce_ex__(self, proto):
+        return object.__reduce_ex__(self, proto)
+
+class C_None_reduce_ex:
+    __reduce_ex__ = None
+
+class C_None_reduce:
+    __reduce__ = None
+
+class C_None_setstate:
+    def __getstate__(self):
+        return 1
+
+    __setstate__ = None
+
+class C_setstate:
+    def __init__(self):
+        self.value = 0
+
+    def __getstate__(self):
+        return self.value
+
+    def __setstate__(self, state):
+        print(state)
+        self.value = state + 1
+
+class PickleReductionMethodsTests(unittest.TestCase):
+    # see gh-93627
+
+    def test_pickle_invalid_reduction_method(self):
+        c = C_None_reduce_ex()
+        with self.assertRaises(TypeError):
+            pickle.dumps(c)
+
+        c = C_None_reduce()
+        with self.assertRaises(TypeError):
+            pickle.dumps(c)
+
+    def test_pickle_invalid_reducer_override(self):
+        obj=C_with_reduce_ex()
+
+        bio = io.BytesIO()
+        pickler = pickle._Pickler(bio)
+        pickler.dump(obj)
+
+        pickler.clear_memo()
+        pickler.reducer_override = None
+        with self.assertRaises(TypeError):
+            pickler.dump(obj)
+
+        pickler.clear_memo()
+        pickler.reducer_override = 10
+        with self.assertRaises(TypeError):
+            pickler.dump(obj)
+
+    def test_pickle_invalid_dispatch_table(self):
+        obj=C_with_reduce_ex()
+
+        bio = io.BytesIO()
+        pickler = pickle._Pickler(bio)
+        pickler.dispatch_table = {type(obj): None}
+        with self.assertRaises(TypeError):
+            pickler.dump(obj)
+
+
+class PickleSetstateTests(unittest.TestCase):
+    # See gh-103035
+
+    def test_pickle_setstate(self):
+        c = C_setstate()
+        s = pickle.dumps(c)
+        c2 = pickle.loads(s)
+        self.assertEqual(c2.value, c.value + 1)
+
+        c = C_None_setstate()
+        p = pickle.dumps(c)
+        with self.assertRaises(TypeError):
+            pickle.loads(p)
+
+
 def load_tests(loader, tests, pattern):
     tests.addTest(doctest.DocTestSuite())
     return tests

Misc/NEWS.d/next/Core and Builtins/2023-03-26-19-11-10.gh-issue-93627.0UgwBL.rst

@@ -0,0 +1 @@
+Update the Python pickle module implementation to match the C implementation of the pickle module. For objects setting reduction methods like :meth:`~object.__reduce_ex__` or :meth:`~object.__reduce__` to ``None``, pickling will result in a :exc:`TypeError`.