Rust python bindings with PyO3: TypeError: argument 'qr': 'QR2d' object cannot be converted to 'QR2d'

[JustinLiang]

I have types.rs:

#[derive(Debug, Clone, PartialEq, Copy)]
pub struct QR<const N: usize> {
    pub value: usize,
}

pub type QR2d = QR<2>;

types_py/lib.rs:

use pyo3::prelude::*;
use types::QR2d

#[pyclass(name = "QR2d")]
#[derive(Clone)]
pub struct PyQR2d(pub QR2d);

#[pymethods]
impl PyQR2d {
    #[new]
    fn new(
        value: usize,
    ) -> Self {
        Self(QR2d {
            value,
        })
    }
}

#[pymodule]
fn types_py_bind(_py: Python, m: &PyModule) -> PyResult<()> {
    m.add_class::<PyQR2d>()?;
    Ok(())
}

Next, I want to use QR2d in my other file lb_py/lib.rs:

use pyo3::prelude::*;
use types_py_rust::PyQR2d;
use primitives::LB2d;


#[pyclass(name = "LB2d")]
pub struct PyLB2d(LB2d);

#[pymethods]
impl PyLB2d {
    #[new]
    fn new(qr: &PyQR2d) -> Self {
        Self(LB2d{qr: qr.0})
    }
}

#[pymodule]
fn lb_py_bind(_py: Python, m: &PyModule) -> PyResult<()> {
    m.add_class::<PyLB2d>()?;
    Ok(())
}

However when I try to do

from project.lb_py import LB2d
from project.types_py import QR2d

qr = QR2d(1)

lb2d = LB2d(qr)

I get the error

    lb2d = LB2d(qr)
E   TypeError: argument 'qr': 'QR2d' object cannot be converted to 'QR2d'

Does anyone know why this is?

[adamreichold]

Does anyone know why this is?

Type objects are currently private to each extension due to the linkage model of Rust, i.e. static linking without a stable ABI. Hence the QR2d type from lb_py is a different type than the QR2d type from types_py.

The easiest way around that is have only one Rust extension and limit reuse to within the Rust code.

Other ways like capsule API as used by other native extensions written in e.g. C/C++ are possible but more involved and currently nothing specifically helpful for Rust/PyO3 exists.

[davidhewitt]

See also #2340

[JustinLiang]

So do you mean I should put everything in a single lib.rs for example:

use qr2d::PyQR2d;
use lb2d::PyLB2d;

#[pymodule]
fn rust_extension(py: Python, m: &PyModule) -> PyResult<()> {
  m.add_class::<PyQR2d>()?;
  m.add_class::<PyLB2d>()?;
  Ok(())
}

[JustinLiang]

thanks a lot for you help, I got it working by doing the above ^^