Code shared from the Rust Playground

playground.rs

use async_std::sync::{Mutex, MutexGuard};
use pyo3::prelude::*;

struct AsyncPyo3 {
    inner: Mutex<()>,
}

struct AsyncGILGuard<'a> {
    _guard: MutexGuard<'a, ()>,
    gil: GILGuard,
}

impl AsyncPyo3 {
    fn new() -> AsyncPyo3 {
        AsyncPyo3 {
            inner: Mutex::new(()),
        }
    }

    async fn acquire_gil(&self) -> AsyncGILGuard<'_> {
        let _guard = self.inner.lock().await;
        let gil = Python::acquire_gil();
        AsyncGILGuard { _guard, gil }
    }
}

impl<'a> AsyncGILGuard<'a> {
    fn python(&self) -> Python {
        self.gil.python()
    }
}

lazy_static::lazy_static! {
    static ref PYO3: AsyncPyo3 = AsyncPyo3::new();
}

#[async_std::main]
async fn main() {
    pyo3::prepare_freethreaded_python();
    let gil = PYO3.acquire_gil().await;
    let py = gil.python();
    let msg = "Hello World!";
    use pyo3::py_run;
    py_run!(py, msg, "print(msg)");
}