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Revert class lookup #7306

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Merged
youknowone merged 2 commits into from
Mar 2, 2026
Merged

Revert class lookup #7306

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863fd73
Revert __class__ lookup skip in object_isinstance
youknowone Mar 1, 2026
864bf57
Collapse nested if in object_isinstance for clippy
youknowone Mar 2, 2026
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Revert __class__ lookup skip in object_isinstance 
The optimization to skip __class__ lookup based on getattro check
was incorrect: a class can override __class__ as a property while
still using standard __getattribute__. Revert to always performing
the lookup, matching CPython's object_isinstance behavior.
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@youknowone
youknowone committed Mar 2, 2026
commit 863fd73034fed799fa1c067e95a71b999a69cabd
35 changes: 10 additions & 25 deletions crates/vm/src/protocol/object.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,8 @@
use crate::{
AsObject, Py, PyObject, PyObjectRef, PyRef, PyResult, TryFromObject, VirtualMachine,
builtins::{
PyBaseObject, PyBytes, PyDict, PyDictRef, PyGenericAlias, PyInt, PyList, PyStr, PyTuple,
PyTupleRef, PyType, PyTypeRef, PyUtf8Str, pystr::AsPyStr,
PyBytes, PyDict, PyDictRef, PyGenericAlias, PyInt, PyList, PyStr, PyTuple, PyTupleRef,
PyType, PyTypeRef, PyUtf8Str, pystr::AsPyStr,
},
common::{hash::PyHash, str::to_ascii},
convert::{ToPyObject, ToPyResult},
Expand Down Expand Up @@ -581,12 +581,8 @@ impl PyObject {
// PyType_Check(cls) - cls is a type object
let mut retval = self.class().is_subtype(cls);
if !retval {
// __class__ is a data descriptor on object that always returns
// obj.class() under standard __getattribute__. Only do the
// expensive attribute lookup when getattro is overridden.
if !self.has_standard_getattro()
&& let Some(i_cls) =
vm.get_attribute_opt(self.to_owned(), identifier!(vm, __class__))?
if let Some(i_cls) =
vm.get_attribute_opt(self.to_owned(), identifier!(vm, __class__))?
&& let Ok(i_cls_type) = PyTypeRef::try_from_object(vm, i_cls)
&& !i_cls_type.is(self.class())
{
Expand All @@ -603,15 +599,13 @@ impl PyObject {
)
})?;

let i_cls: PyObjectRef = if self.has_standard_getattro() {
self.class().to_owned().into()
if let Some(i_cls) =
vm.get_attribute_opt(self.to_owned(), identifier!(vm, __class__))?
{
i_cls.abstract_issubclass(cls, vm)
} else {
match vm.get_attribute_opt(self.to_owned(), identifier!(vm, __class__))? {
Some(cls) => cls,
None => return Ok(false),
}
};
i_cls.abstract_issubclass(cls, vm)
Ok(false)
}
}
}

Expand Down Expand Up @@ -789,15 +783,6 @@ impl PyObject {
Err(vm.new_type_error(format!("'{}' does not support item deletion", self.class())))
}

/// Returns true if the object uses the standard `__getattribute__`
/// (i.e. `object.__getattribute__`), meaning attribute access follows
/// the normal descriptor protocol without custom interception.
#[inline]
fn has_standard_getattro(&self) -> bool {
let getattro = self.class().slots.getattro.load().unwrap();
getattro as usize == PyBaseObject::getattro as *const () as usize
}

/// Equivalent to CPython's _PyObject_LookupSpecial
/// Looks up a special method in the type's MRO without checking instance dict.
/// Returns None if not found (masking AttributeError like CPython).
Expand Down
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