How to get reference to python subclass object wrapped as &PyAny

[shivamka1]

I am trying to use a "serde/serde-json" rust library to serialize and deserialize object to json and vice-versa. Areally simple implementation of which in rust would look something like this:

#[derive(Serialize, Deserialize, Debug, Clone)]
struct Point {
    x: i32,
    y: i32,
}

#[pyfunction]
pub fn point_serde() {
    let point = Point { x: 1, y: 2 };

    let serialized = serde_json::to_string(&point).unwrap();
    println!("serialized = {}", serialized);

    let deserialized: Point = serde_json::from_str(&serialized).unwrap();
    println!("deserialized = {:?}", deserialized);
}

What I am trying to do is allow python users to create say Point objects in python and have it serialized and deserialized in rust like so:

#[derive(Serialize, Deserialize, Debug)]
#[pyclass(subclass)]
pub struct General;

#[pymethods]
impl General {
    #[new]
    fn new() -> Self {
        Self
    }
}

#[pyfunction]
pub fn point_serde(point: &PyCell<General>) -> PyResult<()> {
    let r: &PyAny = point.as_ref();
    println!("{:?}", point.as_ref());

    // let serialized = serde_json::to_string(r).unwrap();
    // println!("serialized = {}", serialized);

    // let deserialized: Point = serde_json::from_str(&serialized).unwrap();
    // println!("deserialized = {:?}", deserialized);

    Ok(())
}

class Point(pyo3_example.General):
    def __new__(cls, x, y):
        return super(Point, cls).__new__(cls)

    def __init__(self, x, y) -> None:
        self.x = x
        self.y = y

pyo3_example.point_serde(Point(3, 2))

This results in Point(3,2).

What I have done here is that I have create a General struct as pyclass that derives Serialize and Deserialize implementations from serde library as a superclass in Rust and Point subclass in python. The intention is to allow any class that extends General have the capability of being serialized and deserialized in rust. Then I have created a pyfunction called point_serde that is supposed to do the actual serialization and deserialization.

When I try to print point.as_ref(), it returns Point(3,2) correctly. But the type is &PyAny. I am unsure how to pass Point to serde_json::to_string(r) as r. Please suggest.

[adamreichold]

This will not work: Serde works by syntactically enumerating the fields at compile time and hence it cannot know about the dynamically created Python properties. I think using a Python-oriented JSON serializer like Python's built-in json module would be preferable.