Workaround for blocked PyObject_GenericSetAttr in metatypes

Python 3.14 introduced a new assertion that prevents us from using PyObject_GenericSetAttr directly in our meta type. To work around this, we manipulate the type dict directly. This workaround is a simplified variant of Cython's workaround from cython/cython#6325. The relevant Python change is in python/cpython#118454
pythonnet · filmor · Feb 24, 2026 · Feb 16, 2026 · Oct 28, 2025 · Nov 24, 2025
commit 08550d090a88f91a84b028208cf57a8a3b9c1b58
diff --git a/src/runtime/Native/PyIdentifier_.cs b/src/runtime/Native/PyIdentifier_.cs
@@ -22,6 +22,8 @@ static class PyIdentifier
          static IntPtr f__self__;
          public static BorrowedReference __self__ => new(f__self__);
          static IntPtr f__annotations__;
+         public static BorrowedReference __dictoffset__ => new(f__dictoffset__);
+         static IntPtr f__dictoffset__;
          public static BorrowedReference __annotations__ => new(f__annotations__);
          static IntPtr f__init__;
          public static BorrowedReference __init__ => new(f__init__);
@@ -54,6 +56,7 @@ static partial class InternString
             "__slots__",
             "__self__",
             "__annotations__",
+            "__dictoffset__",
             "__init__",
             "__repr__",
             "__import__",

diff --git a/src/runtime/Native/PyIdentifier_.tt b/src/runtime/Native/PyIdentifier_.tt
@@ -12,6 +12,7 @@
         "__slots__",
         "__self__",
         "__annotations__",
+        "__dictoffset__",
 
         "__init__",
         "__repr__",

diff --git a/src/runtime/Types/MetaType.cs b/src/runtime/Types/MetaType.cs
@@ -21,6 +21,7 @@ internal sealed class MetaType : ManagedType
         // set in Initialize
         private static PyType PyCLRMetaType;
         private static SlotsHolder _metaSlotsHodler;
+        private static int TypeDictOffset = -1;
 #pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
 
         internal static readonly string[] CustomMethods = new string[]
@@ -35,6 +36,25 @@ internal sealed class MetaType : ManagedType
         public static PyType Initialize()
         {
             PyCLRMetaType = TypeManager.CreateMetaType(typeof(MetaType), out _metaSlotsHodler);
+
+            // Retrieve the offset of the type's dictionary from PyType_Type for
+            // use in the tp_setattro implementation.
+            using (NewReference dictOffset = Runtime.PyObject_GetAttr(Runtime.PyTypeType, PyIdentifier.__dictoffset__))
+            {
+                if (dictOffset.IsNull())
+                {
+                    throw new InvalidOperationException("Could not get __dictoffset__ from PyType_Type");
+                }
+
+                nint dictOffsetVal = Runtime.PyLong_AsSignedSize_t(dictOffset.Borrow());
+                if (dictOffsetVal <= 0)
+                {
+                    throw new InvalidOperationException("Could not get __dictoffset__ from PyType_Type");
+                }
+
+                TypeDictOffset = checked((int)dictOffsetVal);
+            }
+
             return PyCLRMetaType;
         }
 
@@ -44,6 +64,7 @@ public static void Release()
             {
                 _metaSlotsHodler.ResetSlots();
             }
+            TypeDictOffset = -1;
             PyCLRMetaType.Dispose();
         }
 
@@ -287,7 +308,28 @@ public static int tp_setattro(BorrowedReference tp, BorrowedReference name, Borr
                 }
             }
 
-            int res = Runtime.PyObject_GenericSetAttr(tp, name, value);
+            // Access the type's dictionary directly
+            //
+            // We can not use the PyObject_GenericSetAttr because since Python
+            // 3.14 as https://github.com/python/cpython/pull/118454 intrdoduced
+            // an assertion to prevent it from being called from metatypes.
+            //
+            // The direct dictionary access is equivalent to what Cython does
+            // to work around the same issue: https://github.com/cython/cython/pull/6325
+            BorrowedReference typeDict = new(Util.ReadIntPtr(tp, TypeDictOffset));
+            int res;
+            if (value.IsNull)
+            {
+                res = Runtime.PyDict_DelItem(typeDict, name);
+                if (res != 0)
+                {
+                    Exceptions.SetError(Exceptions.AttributeError, "attribute not found");
+                }
+            }
+            else
+            {
+                res = Runtime.PyDict_SetItem(typeDict, name, value);
+            }
             Runtime.PyType_Modified(tp);
 
             return res;

diff --git a/tests/test_array.py b/tests/test_array.py
@@ -1348,7 +1348,6 @@ def test_special_array_creation():
     assert value.Length == 2
 
 
-@pytest.mark.skip
 def test_array_abuse():
     """Test array abuse."""
     _class = Test.PublicArrayTest

diff --git a/tests/test_class.py b/tests/test_class.py
@@ -236,7 +236,6 @@ def __setitem__(self, key, value):
     assert table.Count == 3
 
 
-@pytest.mark.skip
 def test_add_and_remove_class_attribute():
     from System import TimeSpan