Fix bug in default implementation of `__ne__`

guide/src/class/object.md

@@ -73,7 +73,7 @@ impl Number {
 
 In the `__repr__`, we used a hard-coded class name. This is sometimes not ideal,
 because if the class is subclassed in Python, we would like the repr to reflect
-the subclass name. This is typically done in Python code by accessing 
+the subclass name. This is typically done in Python code by accessing
 `self.__class__.__name__`. In order to be able to access the Python type information
 *and* the Rust struct, we need to use a `PyCell` as the `self` argument.
 
@@ -149,8 +149,8 @@ impl Number {
 
 ### Comparisons
 
-Unlike in Python, PyO3 does not provide the magic comparison methods you might expect like `__eq__`,
- `__lt__` and so on. Instead you have to implement all six operations at once with `__richcmp__`.
+PyO3 supports the usual magic comparison methods available in Python such as `__eq__`, `__lt__`
+and so on. It is also possible to support all six operations at once with `__richcmp__`.
 This method will be called with a value of `CompareOp` depending on the operation.
 
 ```rust
@@ -198,13 +198,10 @@ impl Number {
 It checks that the `std::cmp::Ordering` obtained from Rust's `Ord` matches
 the given `CompareOp`.
 
-Alternatively, if you want to leave some operations unimplemented, you can
-return `py.NotImplemented()` for some of the operations:
+Alternatively, you can implement just equality using `__eq__`:
 
 
 ```rust
-use pyo3::class::basic::CompareOp;
-
 # use pyo3::prelude::*;
 #
 # #[pyclass]
@@ -212,14 +209,20 @@ use pyo3::class::basic::CompareOp;
 #
 #[pymethods]
 impl Number {
-    fn __richcmp__(&self, other: &Self, op: CompareOp, py: Python<'_>) -> PyObject {
-        match op {
-            CompareOp::Eq => (self.0 == other.0).into_py(py),
-            CompareOp::Ne => (self.0 != other.0).into_py(py),
-            _ => py.NotImplemented(),
-        }
+    fn __eq__(&self, other: &Self) -> bool {
+        self.0 == other.0
     }
 }
+
+# fn main() -> PyResult<()> {
+#     Python::with_gil(|py| {
+#         let x = PyCell::new(py, Number(4))?;
+#         let y = PyCell::new(py, Number(4))?;
+#         assert!(x.eq(y)?);
+#         assert!(!x.ne(y)?);
+#         Ok(())
+#     })
+# }
 ```
 
 ### Truthyness

guide/src/class/protocols.md

@@ -76,7 +76,8 @@ given signatures should be interpreted as follows:
   - `__richcmp__(<self>, object, pyo3::basic::CompareOp) -> object`
 
     Implements Python comparison operations (`==`, `!=`, `<`, `<=`, `>`, and `>=`) in a single method.
-    The `CompareOp` argument indicates the comparison operation being performed.
+    The `CompareOp` argument indicates the comparison operation being performed. You can use
+    [`CompareOp::matches`] to adapt a Rust `std::cmp::Ordering` result to the requested comparison.
 
     _This method cannot be implemented in combination with any of `__lt__`, `__le__`, `__eq__`, `__ne__`, `__gt__`, or `__ge__`._
 
@@ -84,11 +85,32 @@ given signatures should be interpreted as follows:
     <details>
     <summary>Return type</summary>
     The return type will normally be `PyResult<bool>`, but any Python object can be returned.
+
+    If you want to leave some operations unimplemented, you can return `py.NotImplemented()`
+    for some of the operations:
+
+    ```rust
+    use pyo3::class::basic::CompareOp;
+
+    # use pyo3::prelude::*;
+    #
+    # #[pyclass]
+    # struct Number(i32);
+    #
+    #[pymethods]
+    impl Number {
+        fn __richcmp__(&self, other: &Self, op: CompareOp, py: Python<'_>) -> PyObject {
+            match op {
+                CompareOp::Eq => (self.0 == other.0).into_py(py),
+                CompareOp::Ne => (self.0 != other.0).into_py(py),
+                _ => py.NotImplemented(),
+            }
+        }
+    }
+    ```
+
     If the second argument `object` is not of the type specified in the
     signature, the generated code will automatically `return NotImplemented`.
-
-    You can use [`CompareOp::matches`] to adapt a Rust `std::cmp::Ordering` result
-    to the requested comparison.
     </details>
 
   - `__getattr__(<self>, object) -> object`

pytests/tests/test_comparisons.py

@@ -23,10 +23,14 @@ def test_eq(ty: Type[Union[Eq, PyEq]]):
     c = ty(1)
 
     assert a == b
+    assert not (a != b)
     assert a != c
+    assert not (a == c)
 
     assert b == a
+    assert not (a != b)
     assert b != c
+    assert not (b == c)
 
     with pytest.raises(TypeError):
         assert a <= b
@@ -49,17 +53,21 @@ class PyEqDefaultNe:
         return self.x == other.x
 
 
-@pytest.mark.parametrize("ty", (Eq, PyEq), ids=("rust", "python"))
+@pytest.mark.parametrize("ty", (EqDefaultNe, PyEqDefaultNe), ids=("rust", "python"))
 def test_eq_default_ne(ty: Type[Union[EqDefaultNe, PyEqDefaultNe]]):
     a = ty(0)
     b = ty(0)
     c = ty(1)
 
     assert a == b
+    assert not (a != b)
     assert a != c
+    assert not (a == c)
 
     assert b == a
+    assert not (a != b)
     assert b != c
+    assert not (b == c)
 
     with pytest.raises(TypeError):
         assert a <= b
@@ -152,19 +160,25 @@ def test_ordered_default_ne(ty: Type[Union[OrderedDefaultNe, PyOrderedDefaultNe]
     c = ty(1)
 
     assert a == b
+    assert not (a != b)
     assert a <= b
     assert a >= b
     assert a != c
+    assert not (a == c)
     assert a <= c
 
     assert b == a
+    assert not (b != a)
     assert b <= a
     assert b >= a
     assert b != c
+    assert not (b == c)
     assert b <= c
 
     assert c != a
+    assert not (c == a)
     assert c != b
+    assert not (c == b)
     assert c > a
     assert c >= a
     assert c > b

src/impl_/pyclass.rs

@@ -6,6 +6,7 @@ use crate::{
     internal_tricks::extract_c_string,
     pycell::PyCellLayout,
     pyclass_init::PyObjectInit,
+    types::PyBool,
     Py, PyAny, PyCell, PyClass, PyErr, PyMethodDefType, PyNativeType, PyResult, PyTypeInfo, Python,
 };
 use std::{
@@ -805,11 +806,14 @@ slot_fragment_trait! {
     #[inline]
     unsafe fn __ne__(
         self,
-        _py: Python<'_>,
-        _slf: *mut ffi::PyObject,
-        _other: *mut ffi::PyObject,
+        py: Python<'_>,
+        slf: *mut ffi::PyObject,
+        other: *mut ffi::PyObject,
     ) -> PyResult<*mut ffi::PyObject> {
-        Ok(ffi::_Py_NewRef(ffi::Py_NotImplemented()))
+        // By default `__ne__` will try `__eq__` and invert the result
+        let slf: &PyAny = py.from_borrowed_ptr(slf);
+        let other: &PyAny = py.from_borrowed_ptr(other);
+        slf.eq(other).map(|is_eq| PyBool::new(py, !is_eq).into_ptr())
     }
 }