Return dictionary from Rust to Python

[cassc]

In #[pymethods], is it possible to return a Python dict? It looks like creating PyDict would require access to the global GIL. However, it's not clear how to get the GIL from a function in #[pymthods] or #[pyclass] other than using the deprecated Python::acquire_gil()

[adamreichold]

However, it's not clear how to get the GIL from a function in #[pymthods] or #[pyclass] other than using the deprecated Python::acquire_gil()

There are two answers to this: The replacement for Python::acquire_gil is Python::with_gil which serves the same purpose using a slightly different API (that is easier for us to implement soundly).

However, for #[pyfunction]s and #[pymethod]s, you can just add a parameter py: Python<'_> to get access to the GIL (which is already acquired when such a method is called). Put differently, Python::with_gil is only necessary outside of such Python-visible functions and methods, for example to acquire the GIL on a background thread.

[adamreichold]

Just to add an example:

#[pyfunction]
fn make_dict<'py>(py: Python<'py>, value: i32) -> PyResult<&'py PyDict> {
    let dict = PyDict::new(py);

    dict.set_item("value", value)?;

    Ok(dict)
}

The documentation also contains some hints on how to obtain a Python token under various circumstances, c.f. https://docs.rs/pyo3/latest/pyo3/marker/struct.Python.html#obtaining-a-python-token

[cassc]

This is perfect, thanks so much!