Is there a way (without eval) to access object.__setattr__

[samuelcolvin]

I use object.__setattr__ to set attributes while bypassing a custom __setattr__ method, see here.

My Current logic for doing this in rust is:

static SET_ATTR_CELL: GILOnceCell<PyObject> = GILOnceCell::new();

pub fn get_setattr(py: Python<'_>) -> &PyAny {
    SET_ATTR_CELL
        .get_or_init(py, || py.eval("object.__setattr__", None, None).unwrap().into())
        .as_ref(py)
}

        // Then later
        let setattr = get_setattr(py);
        setattr.call((&instance, intern!(py, "foobar"), foobar), None)?;

I'm wondering if there is a cleaner and more performant way of getting access to object.__setattr__ or a similar method?

The setattr method doesn't work as it doesn't bypass the setattr method on the class/instance in question.

[samuelcolvin]

I've found a work around, what I needed was PyObject_GenericSetAttr, then I implemented my own force_setattr

pub fn force_setattr<N, V>(obj: &PyObject, py: Python<'_>, attr_name: N, value: V) -> PyResult<()>
where
    N: ToPyObject,
    V: ToPyObject,
{
    attr_name.with_borrowed_ptr(py, move |attr_name| {
        value.with_borrowed_ptr(py, |value| unsafe {
            error_on_minusone(py, ffi::PyObject_GenericSetAttr(obj.as_ptr(), attr_name, value))
        })
    })
}

// Defined here as it's not exported by pyo3
#[inline]
fn error_on_minusone(py: Python<'_>, result: c_int) -> PyResult<()> {
    if result != -1 {
        Ok(())
    } else {
        Err(PyErr::fetch(py))
    }
}

[mejrs]

Possibly -can you expand about your use case for this?

[samuelcolvin]

As per the link above, I'm creating pydantic class instances in rust, but pydantic classes have a __setattr__ method to allow valuation on assignment. but when setting __dict__ and __fields_set__ I need to bypass that method.

So basically the rust equivalent of this.

Sorry the code isn't open source yet, should be in the coming days - I'll comment here when it is.

[samuelcolvin]

this is the code in question.

[mejrs]

I'm weakly against adding an api for this. This use case seems pretty niche. And I fear it would be easily confused with setattr 😐 .

[samuelcolvin]

That's fair I think.

[mejrs]

You can get it from object itself:

let setattr = PyModule::import(py, "builtins")?
            .getattr("object")?
            .getattr("__setattr__")?;