When we write vanilla rust and we have to pass in an async function as an argument to another function we do the following:
pub f<F,'a>(
test: &dyn Fn(&'a mut String, String, String, TcpStream) -> F,
) where
F: Future<Output = ()> + 'a,
But when I do the same on a #![pyfunction]
expecting to get an async python function, I am getting an error.
e.g async def fn():
....
On reading the docs of PyO3, I found out that I can include PyAny
as a param.
But, on implementing the following function:
pub fn start_server(test: PyAny) {
test.call0();
}
I get the following error.
[rustc E0277] [E] the trait bound `pyo3::PyAny: pyo3::FromPyObject<'_>` is not satisfied
expected an implementor of trait `pyo3::FromPyObject<'_>`
note: required because of the requirements on the impl of `pyo3::FromPyObject<'_>` for `pyo3::PyAny`
How can I implement this in my code. I would understand if this is not possible, if that is the case, I would request you to please recommend me an alternative.
UPDATE:
I have found an alternative where I create an empty struct and call the method in the following way. But I would really appreciate if I can get through without creating an empty struct.
#[pymethods]
impl Server {
#[new]
fn new() -> Self {
Self {}
}
fn start(mut self_: PyRefMut<Self>, test: &PyAny) {
test.call0();
}
}
But on passing an async function as param gives an error of
RuntimeWarning: coroutine
s.start(h)
RuntimeWarning: Enable tracemalloc to get the object allocation traceback
Your function needs to take a reference, ie &PyAny
. PyAny
as an owned value does not implement FromPyObject
, which is why you got the error.
// lib.rs
use pyo3::prelude::*;
use pyo3::wrap_pyfunction;
#[pyfunction]
fn foo(x: &PyAny) -> PyResult<&PyAny> {
x.call0()
}
#[pymodule]
fn async_pyo3(py: Python, m: &PyModule) -> PyResult<()> {
m.add_function(wrap_pyfunction!(foo, m)?).unwrap();
Ok(())
}
import async_pyo3
async def bar():
return "foo"
awaitable = async_pyo3.foo(bar) # <coroutine object bar at 0x7f8f6aa01340>
print(await awaitable) # "foo"
As such, the fix of moving it to an method on Server
most likely was not the fix, but just coincidence since you changed test
to &PyAny
.
There is a whole section in the PyO3 documentation about integrating Python and Rust async / await
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