Allow omitting PyResult wrapping in property get/set methods

fixes #443

CHANGELOG.md

@@ -11,6 +11,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
  * Have `PyModule` generate an index of its members (`__all__` list).
 
+### Changed
+
+ * Methods decorated with `#[getter]` and `#[setter]` can now omit wrapping the
+   result type in `PyResult` if they don't raise exceptions.
+
 ### Fixed
 
  * `type_object::PyTypeObject` has been marked unsafe because breaking the contract `type_object::PyTypeObject::init_type` can lead to UB.

pyo3-derive-backend/src/pymethod.rs

@@ -273,7 +273,9 @@ pub(crate) fn impl_wrap_getter(cls: &syn::Type, name: &syn::Ident) -> TokenStrea
             let _py = pyo3::Python::assume_gil_acquired();
             let _slf = _py.mut_from_borrowed_ptr::<#cls>(_slf);
 
-            match _slf.#name() {
+            let result = pyo3::derive_utils::IntoPyResult::into_py_result(_slf.#name());
+
+            match result {
                 Ok(val) => {
                     pyo3::IntoPyPointer::into_ptr(val.into_object(_py))
                 }
@@ -314,7 +316,9 @@ pub(crate) fn impl_wrap_setter(
             let _value = _py.from_borrowed_ptr(_value);
 
             let _result = match <#val_ty as pyo3::FromPyObject>::extract(_value) {
-                Ok(_val) => _slf.#name(_val),
+                Ok(_val) => {
+                    pyo3::derive_utils::IntoPyResult::into_py_result(_slf.#name(_val))
+                }
                 Err(e) => Err(e)
             };
             match _result {

tests/test_getter_setter.rs

@@ -26,6 +26,16 @@ impl ClassWithProperties {
         self.num = value;
         Ok(())
     }
+
+    #[getter]
+    /// a getter with a type un-wrapped by PyResult
+    fn get_unwrapped(&self) -> i32 {
+        self.num
+    }
+    #[setter]
+    fn set_unwrapped(&mut self, value: i32) {
+        self.num = value;
+    }
 }
 
 #[test]
@@ -41,6 +51,10 @@ fn class_with_properties() {
     py_run!(py, inst, "assert inst.get_num() == 20");
     py_run!(py, inst, "assert inst.get_num() == inst.DATA");
 
+    py_run!(py, inst, "assert inst.get_num() == inst.unwrapped == 20");
+    py_run!(py, inst, "inst.unwrapped = 42");
+    py_run!(py, inst, "assert inst.get_num() == inst.unwrapped == 42");
+
     let d = [("C", py.get_type::<ClassWithProperties>())].into_py_dict(py);
     py.run(
         "assert C.DATA.__doc__ == 'a getter for data'",