lib.rs

use pyo3::prelude::*;
#[allow(dead_code)]
#[pyclass]
pub struct State {
    pub x: usize,
    pub y: usize,
    pub z: usize,
}

#[pymodule]
fn py_test(py: Python, m: &PyModule) -> PyResult<()> {
    m.add_class::<State>()?;
    #[pyfn(m, "sum_as_string")]
    fn sum_as_string(py: Python, a: usize, b: usize, callback: PyObject) -> PyResult<PyObject> {
        println!("Hello from Rust!");
        let state = Py::new(
            py,
            State {
                x: a,
                y: b,
                z: a + b,
            },
        )
        .unwrap();
        callback.call(py, (state,), None)
    }
    Ok(())
}