Help creating a class that have an attribute that is a list of strings than I can mutate from python

[prokie]

I have read the documentation at https://pyo3.rs/v0.22.2/faq#pyo3get-clones-my-field but I still can not figure out how to solve my issue. I have tried with this in lib.rs

use pyo3::prelude::*;

#[pyclass]
struct Example {
    #[pyo3(get, set)]
    vector: Vec<String>,
}

#[pymethods]
impl Example {
    #[new]
    fn new() -> Self {
        Self { vector: Vec::new() }
    }
}

#[pymodule]
fn hejhej(m: &Bound<'_, PyModule>) -> PyResult<()> {
    m.add_class::<Example>()?;
    Ok(())
}

And this in python is what happens in python, which I guess is expected.

>>> from example import Example
>>> example = Example()
>>> print(example.vector)
[]
>>> example.vector.append("asd")
>>> print(example.vector)
[]

By reading the documentation I can see that I need to wrap my vector with Py<> but then I do not know how to create my new function. I tried this but it does not work.

#[new]
fn __new__(py: Python<'_>) -> PyResult<Self> {
    Ok(Self {
        vector: Py::new(py, vec![])?,
    })
}

[LilyFoote]

Did you update your Example struct so vector has type Py<Vec<String>>?

[prokie]

You mean like this?

use pyo3::prelude::*;

#[pyclass]
struct Example {
    #[pyo3(get, set)]
    vector: Py<Vec<String>>,
}

#[pymethods]
impl Example {
    #[new]
    fn __new__(py: Python<'_>) -> PyResult<Self> {
        Ok(Self {
            vector: Py::new(py, vec![])?,
        })
    }
}

#[pymodule]
fn hej(m: &Bound<'_, PyModule>) -> PyResult<()> {
    m.add_class::<Example>()?;
    Ok(())
}

Then I get the following errors

error[E0277]: the trait bound `Vec<_>: Into<PyClassInitializer<Vec<_>>>` is not satisfied
   --> src\lib.rs:14:33
    |
14  |             vector: Py::new(py, vec![])?,
    |                     -------     ^^^^^^ the trait `PyClass` is not implemented for `Vec<_>`, which is required by `Vec<_>: Into<PyClassInitializer<_>>`
    |                     |
    |                     required by a bound introduced by this call
    |
    = note: required for `PyClassInitializer<Vec<_>>` to implement `From<Vec<_>>`
    = note: required for `Vec<_>` to implement `Into<PyClassInitializer<Vec<_>>>`

And from here I do not know how to continue. :(

[mejrs]

It's not the way to do it. Lily asked if you did, not that you should. Something like

#[pyclass]
struct Example {
    #[pyo3(get, set)]
    vector: Py<PyList>,
}

probably does. If you need different behavior from a python list you can make a newtype around a Vec.

[prokie]

You are right, I misunderstood her.

Yes using <PyList> I can now get this to compile and I can get mutate vector from Python, that is just what I wanted.

Thanks so much!

use pyo3::{prelude::*, types::PyList};

#[pyclass]
struct Example {
    #[pyo3(get, set)]
    vector: Py<PyList>,
}

#[pymethods]
impl Example {
    #[new]
    fn __new__(py: Python<'_>) -> Self {
        Self {
            vector: PyList::empty_bound(py).unbind(),
        }
    }
}

#[pymodule]
fn example(m: &Bound<'_, PyModule>) -> PyResult<()> {
    m.add_class::<Example>()?;
    Ok(())
}