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Protocols: implement __getattribute__ 

converting tp_getattro to a shared slot

Fixes #2186
This commit is contained in:
Georg Brandl 2022-02-25 18:52:36 +01:00
parent 03dc96bff1
commit 0678f11266
6 changed files with 158 additions and 29 deletions
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1
CHANGELOG.md
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@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
- `wrap_pyfunction!` can now wrap a `#[pyfunction]` which is implemented in a different Rust module or crate. [#2091](https://github.com/PyO3/pyo3/pull/2091)
- Add `PyAny::contains` method (`in` operator for `PyAny`). [#2115](https://github.com/PyO3/pyo3/pull/2115)
- Add `PyMapping::contains` method (`in` operator for `PyMapping`). [#2133](https://github.com/PyO3/pyo3/pull/2133)
- Add support for the `__getattribute__` magic method. [#2187](https://github.com/PyO3/pyo3/pull/2187)
- Add garbage collection magic methods `__traverse__` and `__clear__` to `#[pymethods]`. [#2159](https://github.com/PyO3/pyo3/pull/2159)
- Add support for `from_py_with` on struct tuples and enums to override the default from-Python conversion. [#2181](https://github.com/PyO3/pyo3/pull/2181)
- Add `eq`, `ne`, `lt`, `le`, `gt`, `ge` methods to `PyAny` that wrap `rich_compare`. [#2175](https://github.com/PyO3/pyo3/pull/2175)

10
guide/src/class/protocols.md
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@ -75,6 +75,16 @@ given signatures should be interpreted as follows:
</details>
- `__getattr__(<self>, object) -> object`
- `__getattribute__(<self>, object) -> object`
<details>
<summary>Differences between `__getattr__` and `__getattribute__`</summary>
As in Python, `__getattr__` is only called if the attribute is not found
by normal attribute lookup. `__getattribute__`, on the other hand, is
called for *every* attribute access. If it wants to access existing
attributes on `self`, it needs to be very careful not to introduce
infinite recursion, and use `baseclass.__getattribute__()`.
</details>
- `__setattr__(<self>, value: object) -> ()`
- `__delattr__(<self>, object) -> ()`

5
pyo3-macros-backend/src/pyimpl.rs
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@ -242,6 +242,11 @@ fn add_shared_proto_slots(
}};
}
try_add_shared_slot!(
"__getattribute__",
"__getattr__",
generate_pyclass_getattro_slot
);
try_add_shared_slot!("__setattr__", "__delattr__", generate_pyclass_setattr_slot);
try_add_shared_slot!("__set__", "__delete__", generate_pyclass_setdescr_slot);
try_add_shared_slot!("__setitem__", "__delitem__", generate_pyclass_setitem_slot);

33
pyo3-macros-backend/src/pymethod.rs
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@ -38,7 +38,6 @@ impl PyMethodKind {
fn from_name(name: &str) -> Self {
match name {
// Protocol implemented through slots
"__getattr__" => PyMethodKind::Proto(PyMethodProtoKind::Slot(&__GETATTR__)),
"__str__" => PyMethodKind::Proto(PyMethodProtoKind::Slot(&__STR__)),
"__repr__" => PyMethodKind::Proto(PyMethodProtoKind::Slot(&__REPR__)),
"__hash__" => PyMethodKind::Proto(PyMethodProtoKind::Slot(&__HASH__)),
@ -85,6 +84,10 @@ impl PyMethodKind {
"__releasebuffer__" => PyMethodKind::Proto(PyMethodProtoKind::Slot(&__RELEASEBUFFER__)),
"__clear__" => PyMethodKind::Proto(PyMethodProtoKind::Slot(&__CLEAR__)),
// Protocols implemented through traits
"__getattribute__" => {
PyMethodKind::Proto(PyMethodProtoKind::SlotFragment(&__GETATTRIBUTE__))
}
"__getattr__" => PyMethodKind::Proto(PyMethodProtoKind::SlotFragment(&__GETATTR__)),
"__setattr__" => PyMethodKind::Proto(PyMethodProtoKind::SlotFragment(&__SETATTR__)),
"__delattr__" => PyMethodKind::Proto(PyMethodProtoKind::SlotFragment(&__DELATTR__)),
"__set__" => PyMethodKind::Proto(PyMethodProtoKind::SlotFragment(&__SET__)),
@ -570,21 +573,6 @@ impl PropertyType<'_> {
}
}
const __GETATTR__: SlotDef = SlotDef::new("Py_tp_getattro", "getattrofunc")
.arguments(&[Ty::Object])
.before_call_method(TokenGenerator(|| {
quote! {
// Behave like python's __getattr__ (as opposed to __getattribute__) and check
// for existing fields and methods first
let existing = _pyo3::ffi::PyObject_GenericGetAttr(_slf, arg0);
if existing.is_null() {
// PyObject_HasAttr also tries to get an object and clears the error if it fails
_pyo3::ffi::PyErr_Clear();
} else {
return existing;
}
}
}));
const __STR__: SlotDef = SlotDef::new("Py_tp_str", "reprfunc");
const __REPR__: SlotDef = SlotDef::new("Py_tp_repr", "reprfunc");
const __HASH__: SlotDef = SlotDef::new("Py_tp_hash", "hashfunc")
@ -870,7 +858,6 @@ struct SlotDef {
func_ty: StaticIdent,
arguments: &'static [Ty],
ret_ty: Ty,
before_call_method: Option<TokenGenerator>,
extract_error_mode: ExtractErrorMode,
return_mode: Option<ReturnMode>,
require_unsafe: bool,
@ -885,7 +872,6 @@ impl SlotDef {
func_ty: StaticIdent(func_ty),
arguments: NO_ARGUMENTS,
ret_ty: Ty::Object,
before_call_method: None,
extract_error_mode: ExtractErrorMode::Raise,
return_mode: None,
require_unsafe: false,
@ -902,11 +888,6 @@ impl SlotDef {
self
}
const fn before_call_method(mut self, before_call_method: TokenGenerator) -> Self {
self.before_call_method = Some(before_call_method);
self
}
const fn return_conversion(mut self, return_conversion: TokenGenerator) -> Self {
self.return_mode = Some(ReturnMode::Conversion(return_conversion));
self
@ -936,7 +917,6 @@ impl SlotDef {
let SlotDef {
slot,
func_ty,
before_call_method,
arguments,
extract_error_mode,
ret_ty,
@ -963,7 +943,6 @@ impl SlotDef {
Ok(quote!({
unsafe extern "C" fn __wrap(_raw_slf: *mut _pyo3::ffi::PyObject, #(#method_arguments),*) -> #ret_ty {
let _slf = _raw_slf;
#before_call_method
let gil = _pyo3::GILPool::new();
let #py = gil.python();
_pyo3::callback::panic_result_into_callback_output(#py, ::std::panic::catch_unwind(move || -> _pyo3::PyResult<_> {
@ -1074,6 +1053,10 @@ impl SlotFragmentDef {
}
}
const __GETATTRIBUTE__: SlotFragmentDef =
SlotFragmentDef::new("__getattribute__", &[Ty::Object]).ret_ty(Ty::Object);
const __GETATTR__: SlotFragmentDef =
SlotFragmentDef::new("__getattr__", &[Ty::Object]).ret_ty(Ty::Object);
const __SETATTR__: SlotFragmentDef =
SlotFragmentDef::new("__setattr__", &[Ty::Object, Ty::NonNullObject]);
const __DELATTR__: SlotFragmentDef = SlotFragmentDef::new("__delattr__", &[Ty::Object]);

76
src/impl_/pyclass.rs
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@ -5,7 +5,7 @@ use crate::{
pycell::PyCellLayout,
pyclass_init::PyObjectInit,
type_object::{PyLayout, PyTypeObject},
PyCell, PyClass, PyMethodDefType, PyNativeType, PyResult, PyTypeInfo, Python,
Py, PyAny, PyCell, PyClass, PyErr, PyMethodDefType, PyNativeType, PyResult, PyTypeInfo, Python,
};
use std::{
marker::PhantomData,
@ -198,6 +198,80 @@ macro_rules! slot_fragment_trait {
}
}
slot_fragment_trait! {
PyClass__getattribute__SlotFragment,
/// # Safety: _slf and _attr must be valid non-null Python objects
#[inline]
unsafe fn __getattribute__(
self,
py: Python,
slf: *mut ffi::PyObject,
attr: *mut ffi::PyObject,
) -> PyResult<*mut ffi::PyObject> {
let res = ffi::PyObject_GenericGetAttr(slf, attr);
if res.is_null() { Err(PyErr::fetch(py)) }
else { Ok(res) }
}
}
slot_fragment_trait! {
PyClass__getattr__SlotFragment,
/// # Safety: _slf and _attr must be valid non-null Python objects
#[inline]
unsafe fn __getattr__(
self,
py: Python,
_slf: *mut ffi::PyObject,
attr: *mut ffi::PyObject,
) -> PyResult<*mut ffi::PyObject> {
Err(PyErr::new::<PyAttributeError, _>((Py::<PyAny>::from_owned_ptr(py, attr),)))
}
}
#[doc(hidden)]
#[macro_export]
macro_rules! generate_pyclass_getattro_slot {
($cls:ty) => {{
unsafe extern "C" fn __wrap(
_slf: *mut $crate::ffi::PyObject,
attr: *mut $crate::ffi::PyObject,
) -> *mut $crate::ffi::PyObject {
use ::std::result::Result::*;
use $crate::callback::IntoPyCallbackOutput;
use $crate::impl_::pyclass::*;
let gil = $crate::GILPool::new();
let py = gil.python();
$crate::callback::panic_result_into_callback_output(
py,
::std::panic::catch_unwind(move || -> $crate::PyResult<_> {
let collector = PyClassImplCollector::<$cls>::new();
// Strategy:
// - Try __getattribute__ first. Its default is PyObject_GenericGetAttr.
// - If it returns a result, use it.
// - If it fails with AttributeError, try __getattr__.
// - If it fails otherwise, reraise.
match collector.__getattribute__(py, _slf, attr) {
Ok(obj) => obj.convert(py),
Err(e) if e.is_instance_of::<$crate::exceptions::PyAttributeError>(py) => {
collector.__getattr__(py, _slf, attr).convert(py)
}
Err(e) => Err(e),
}
}),
)
}
$crate::ffi::PyType_Slot {
slot: $crate::ffi::Py_tp_getattro,
pfunc: __wrap as $crate::ffi::getattrofunc as _,
}
}};
}
pub use generate_pyclass_getattro_slot;
/// Macro which expands to three items
/// - Trait for a __setitem__ dunder
/// - Trait for the corresponding __delitem__ dunder

62
tests/test_proto_methods.rs
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@ -1,9 +1,8 @@
#![cfg(feature = "macros")]
use pyo3::exceptions::{PyIndexError, PyValueError};
use pyo3::exceptions::{PyAttributeError, PyIndexError, PyValueError};
use pyo3::types::{PyDict, PyList, PyMapping, PySequence, PySlice, PyType};
use pyo3::{exceptions::PyAttributeError, prelude::*};
use pyo3::{py_run, PyCell};
use pyo3::{prelude::*, py_run, PyCell};
use std::{isize, iter};
mod common;
@ -606,6 +605,63 @@ fn getattr_doesnt_override_member() {
py_assert!(py, inst, "inst.a == 8");
}
#[pyclass]
struct ClassWithGetAttribute {
#[pyo3(get, set)]
data: u32,
}
#[pymethods]
impl ClassWithGetAttribute {
fn __getattribute__(&self, _name: &str) -> u32 {
self.data * 2
}
}
#[test]
fn getattribute_overrides_member() {
let gil = Python::acquire_gil();
let py = gil.python();
let inst = PyCell::new(py, ClassWithGetAttribute { data: 4 }).unwrap();
py_assert!(py, inst, "inst.data == 8");
py_assert!(py, inst, "inst.y == 8");
}
#[pyclass]
struct ClassWithGetAttrAndGetAttribute;
#[pymethods]
impl ClassWithGetAttrAndGetAttribute {
fn __getattribute__(&self, name: &str) -> PyResult<u32> {
if name == "exists" {
Ok(42)
} else if name == "error" {
Err(PyValueError::new_err("bad"))
} else {
Err(PyAttributeError::new_err("fallback"))
}
}
fn __getattr__(&self, name: &str) -> PyResult<u32> {
if name == "lucky" {
Ok(57)
} else {
Err(PyAttributeError::new_err("no chance"))
}
}
}
#[test]
fn getattr_and_getattribute() {
let gil = Python::acquire_gil();
let py = gil.python();
let inst = PyCell::new(py, ClassWithGetAttrAndGetAttribute).unwrap();
py_assert!(py, inst, "inst.exists == 42");
py_assert!(py, inst, "inst.lucky == 57");
py_expect_exception!(py, inst, "inst.error", PyValueError);
py_expect_exception!(py, inst, "inst.unlucky", PyAttributeError);
}
/// Wraps a Python future and yield it once.
#[pyclass]
#[derive(Debug)]