gh-93627: Align Python implementation of pickle with C implementation of pickle (GH-103035)

If a method like __reduce_ex_ or __reduce__ is set to None, a TypeError is raised.

Author: eendebakpt

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/pickletester.py

@@ -2408,6 +2408,22 @@ def test_reduce_calls_base(self):
             y = self.loads(s)
             self.assertEqual(y._reduce_called, 1)
 
+    def test_reduce_ex_None(self):
+        c = REX_None()
+        with self.assertRaises(TypeError):
+            self.dumps(c)
+
+    def test_reduce_None(self):
+        c = R_None()
+        with self.assertRaises(TypeError):
+            self.dumps(c)
+
+    def test_pickle_setstate_None(self):
+        c = C_None_setstate()
+        p = self.dumps(c)
+        with self.assertRaises(TypeError):
+            self.loads(p)
+
     @no_tracing
     def test_bad_getattr(self):
         # Issue #3514: crash when there is an infinite loop in __getattr__
@@ -3349,6 +3365,21 @@ def __setstate__(self, state):
     def __reduce__(self):
         return type(self), (), self.state
 
+class REX_None:
+    """ Setting __reduce_ex__ to None should fail """
+    __reduce_ex__ = None
+
+class R_None:
+    """ Setting __reduce__ to None should fail """
+    __reduce__ = None
+
+class C_None_setstate:
+    """  Setting __setstate__ to None should fail """
+    def __getstate__(self):
+        return 1
+
+    __setstate__ = None
+
 
 # Test classes for newobj
 
@@ -3752,6 +3783,25 @@ def test_unpickling_buffering_readline(self):
                 unpickler = self.unpickler_class(f)
                 self.assertEqual(unpickler.load(), data)
 
+    def test_pickle_invalid_reducer_override(self):
+        # gh-103035
+        obj = object()
+
+        f = io.BytesIO()
+        class MyPickler(self.pickler_class):
+            pass
+        pickler = MyPickler(f)
+        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)
 
 # Tests for dispatch_table attribute
 
@@ -3914,6 +3964,15 @@ def dumps(obj, protocol=None):
 
         self._test_dispatch_table(dumps, dt)
 
+    def test_dispatch_table_None_item(self):
+        # gh-93627
+        obj = object()
+        f = io.BytesIO()
+        pickler = self.pickler_class(f)
+        pickler.dispatch_table = {type(obj): None}
+        with self.assertRaises(TypeError):
+            pickler.dump(obj)
+
     def _test_dispatch_table(self, dumps, dispatch_table):
         def custom_load_dump(obj):
             return pickle.loads(dumps(obj, 0))

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`.