RustPython · youknowone · Mar 19, 2026 · Mar 13, 2026 · Mar 18, 2026 · Mar 18, 2026
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
@@ -262,7 +262,6 @@ def __contains__(self, key):
         d = c.new_child(b=20, c=30)
         self.assertEqual(d.maps, [{'b': 20, 'c': 30}, {'a': 1, 'b': 2}])
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; AssertionError: <class 'test.test_collections.TestChainMap.test_union_operators.<locals>.Subclass'> is not <class 'collections.ChainMap'>
     def test_union_operators(self):
         cm1 = ChainMap(dict(a=1, b=2), dict(c=3, d=4))
         cm2 = ChainMap(dict(a=10, e=5), dict(b=20, d=4))

diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
@@ -4318,7 +4318,6 @@ class C:
         C.__name__ = Nasty("abc")
         C.__name__ = "normal"
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON
     def test_subclass_right_op(self):
         # Testing correct dispatch of subclass overloading __r<op>__...
 

diff --git a/crates/vm/src/protocol/number.rs b/crates/vm/src/protocol/number.rs
@@ -229,12 +229,63 @@ pub enum PyNumberBinaryOp {
     InplaceMatrixMultiply,
 }
 
+impl PyNumberBinaryOp {
+    /// Returns `None` for in-place ops which don't have right-side variants.
+    pub fn right_method_name(
+        self,
+        vm: &VirtualMachine,
+    ) -> Option<&'static crate::builtins::PyStrInterned> {
+        use PyNumberBinaryOp::*;
+        Some(match self {
+            Add => identifier!(vm, __radd__),
+            Subtract => identifier!(vm, __rsub__),
+            Multiply => identifier!(vm, __rmul__),
+            Remainder => identifier!(vm, __rmod__),
+            Divmod => identifier!(vm, __rdivmod__),
+            Lshift => identifier!(vm, __rlshift__),
+            Rshift => identifier!(vm, __rrshift__),
+            And => identifier!(vm, __rand__),
+            Xor => identifier!(vm, __rxor__),
+            Or => identifier!(vm, __ror__),
+            FloorDivide => identifier!(vm, __rfloordiv__),
+            TrueDivide => identifier!(vm, __rtruediv__),
+            MatrixMultiply => identifier!(vm, __rmatmul__),
+            // In-place ops don't have right-side variants
+            InplaceAdd
+            | InplaceSubtract
+            | InplaceMultiply
+            | InplaceRemainder
+            | InplaceLshift
+            | InplaceRshift
+            | InplaceAnd
+            | InplaceXor
+            | InplaceOr
+            | InplaceFloorDivide
+            | InplaceTrueDivide
+            | InplaceMatrixMultiply => return None,
+        })
+    }
+}
+
 #[derive(Copy, Clone)]
 pub enum PyNumberTernaryOp {
     Power,
     InplacePower,
 }
 
+impl PyNumberTernaryOp {
+    /// Returns `None` for in-place ops which don't have right-side variants.
+    pub fn right_method_name(
+        self,
+        vm: &VirtualMachine,
+    ) -> Option<&'static crate::builtins::PyStrInterned> {
+        Some(match self {
+            PyNumberTernaryOp::Power => identifier!(vm, __rpow__),
+            PyNumberTernaryOp::InplacePower => return None,
+        })
+    }
+}
+
 #[derive(Default)]
 pub struct PyNumberSlots {
     pub add: AtomicCell<Option<PyNumberBinaryFunc>>,

diff --git a/crates/vm/src/vm/vm_ops.rs b/crates/vm/src/vm/vm_ops.rs
@@ -1,14 +1,32 @@
 use super::VirtualMachine;
 use crate::stdlib::_warnings;
 use crate::{
-    PyRef,
-    builtins::{PyInt, PyStr, PyStrRef, PyUtf8Str},
+    Py, PyRef,
+    builtins::{PyInt, PyStr, PyStrInterned, PyStrRef, PyType, PyUtf8Str},
     object::{AsObject, PyObject, PyObjectRef, PyResult},
     protocol::{PyNumberBinaryOp, PyNumberTernaryOp},
     types::PyComparisonOp,
 };
 use num_traits::ToPrimitive;
 
+/// [CPython `method_is_overloaded`](https://github.com/python/cpython/blob/v3.14.3/Objects/typeobject.c#L9849-L9879)
+fn method_is_overloaded(
+    class_a: &Py<PyType>,
+    class_b: &Py<PyType>,
+    rop_name: Option<&'static PyStrInterned>,
+    vm: &VirtualMachine,
+) -> PyResult<bool> {
+    let Some(rop_name) = rop_name else {
+        return Ok(false);
+    };
+    let Some(method_b) = class_b.get_attr(rop_name) else {
+        return Ok(false);
+    };
+    class_a.get_attr(rop_name).map_or(Ok(true), |method_a| {
+        vm.identical_or_equal(&method_a, &method_b).map(|eq| !eq)
+    })
+}
+
 macro_rules! binary_func {
     ($fn:ident, $op_slot:ident, $op:expr) => {
         pub fn $fn(&self, a: &PyObject, b: &PyObject) -> PyResult {
@@ -162,18 +180,34 @@ impl VirtualMachine {
 
         // Number slots are inherited, direct access is O(1)
         let slot_a = class_a.slots.as_number.left_binary_op(op_slot);
+        let slot_a_addr = slot_a.map(|x| x as usize);
         let mut slot_b = None;
+        let left_b_addr;
 
         if !class_a.is(class_b) {
             let slot_bb = class_b.slots.as_number.right_binary_op(op_slot);
-            if slot_bb.map(|x| x as usize) != slot_a.map(|x| x as usize) {
+            if slot_bb.map(|x| x as usize) != slot_a_addr {
                 slot_b = slot_bb;
             }
+            left_b_addr = class_b
+                .slots
+                .as_number
+                .left_binary_op(op_slot)
+                .map(|x| x as usize);
+        } else {
+            left_b_addr = slot_a_addr;
         }
 
         if let Some(slot_a) = slot_a {
             if let Some(slot_bb) = slot_b
                 && class_b.fast_issubclass(class_a)
+                && (slot_a_addr != left_b_addr
+                    || method_is_overloaded(
+                        class_a,
+                        class_b,
+                        op_slot.right_method_name(self),
+                        self,
+                    )?)
             {
                 let ret = slot_bb(a, b, self)?;
                 if !ret.is(&self.ctx.not_implemented) {
@@ -269,18 +303,34 @@ impl VirtualMachine {
 
         // Number slots are inherited, direct access is O(1)
         let slot_a = class_a.slots.as_number.left_ternary_op(op_slot);
+        let slot_a_addr = slot_a.map(|x| x as usize);
         let mut slot_b = None;
+        let left_b_addr;
 
         if !class_a.is(class_b) {
             let slot_bb = class_b.slots.as_number.right_ternary_op(op_slot);
-            if slot_bb.map(|x| x as usize) != slot_a.map(|x| x as usize) {
+            if slot_bb.map(|x| x as usize) != slot_a_addr {
                 slot_b = slot_bb;
             }
+            left_b_addr = class_b
+                .slots
+                .as_number
+                .left_ternary_op(op_slot)
+                .map(|x| x as usize);
+        } else {
+            left_b_addr = slot_a_addr;
         }
 
         if let Some(slot_a) = slot_a {
             if let Some(slot_bb) = slot_b
                 && class_b.fast_issubclass(class_a)
+                && (slot_a_addr != left_b_addr
+                    || method_is_overloaded(
+                        class_a,
+                        class_b,
+                        op_slot.right_method_name(self),
+                        self,
+                    )?)
             {
                 let ret = slot_bb(a, b, c, self)?;
                 if !ret.is(&self.ctx.not_implemented) {