None.__ne__(None) should be NotImplemented (#5124)

extra_tests/snippets/builtin_none.py

@@ -22,4 +22,4 @@ assert type(None)() is None
 assert None.__eq__(3) is NotImplemented
 assert None.__ne__(3) is NotImplemented
 assert None.__eq__(None) is True
-# assert None.__ne__(None) is False  # changed in 3.12
+assert None.__ne__(None) is NotImplemented

vm/src/builtins/singletons.rs

@@ -2,9 +2,10 @@ use super::{PyStrRef, PyType, PyTypeRef};
 use crate::{
     class::PyClassImpl,
     convert::ToPyObject,
+    function::{PyArithmeticValue, PyComparisonValue},
     protocol::PyNumberMethods,
-    types::{AsNumber, Constructor, Representable},
-    Context, Py, PyObjectRef, PyPayload, PyResult, VirtualMachine,
+    types::{AsNumber, Comparable, Constructor, PyComparisonOp, Representable},
+    Context, Py, PyObject, PyObjectRef, PyPayload, PyResult, VirtualMachine,
 };
 
 #[pyclass(module = false, name = "NoneType")]
@@ -42,7 +43,7 @@ impl Constructor for PyNone {
     }
 }
 
-#[pyclass(with(Constructor, AsNumber, Representable))]
+#[pyclass(with(Constructor, Comparable, AsNumber, Representable))]
 impl PyNone {
     #[pymethod(magic)]
     fn bool(&self) -> bool {
@@ -72,6 +73,28 @@ impl AsNumber for PyNone {
     }
 }
 
+impl Comparable for PyNone {
+    fn cmp(
+        _zelf: &Py<Self>,
+        other: &PyObject,
+        op: PyComparisonOp,
+        vm: &VirtualMachine,
+    ) -> PyResult<PyComparisonValue> {
+        let value = match op {
+            PyComparisonOp::Eq => {
+                if vm.is_none(other) {
+                    PyArithmeticValue::Implemented(true)
+                } else {
+                    PyArithmeticValue::NotImplemented
+                }
+            }
+            _ => PyComparisonValue::NotImplemented,
+        };
+
+        Ok(value)
+    }
+}
+
 #[pyclass(module = false, name = "NotImplementedType")]
 #[derive(Debug)]
 pub struct PyNotImplemented;