pyo3/tests/ui/invalid_closure.rs

use pyo3::prelude::*;
use pyo3::types::{PyCFunction, PyDict, PyTuple};

fn main() {
    let fun: Py<PyCFunction> = Python::with_gil(|py| {
        let local_data = vec![0, 1, 2, 3, 4];
        let ref_: &[u8] = &local_data;

        let closure_fn = |_args: &PyTuple, _kwargs: Option<&PyDict>| -> PyResult<()> {
            println!("This is five: {:?}", ref_.len());
            Ok(())
        };
        PyCFunction::new_closure(py, None, None, closure_fn).unwrap().into()
    });

    Python::with_gil(|py| {
        fun.call0(py).unwrap();
    });
}