pyo3/guide/src/python_from_rust.md

Calling Python in Rust code

These APIs work from Rust whenever you have a Python object handy, whether PyO3 is built for an extension module or not.

Want to run just an expression? Then use eval.

Python::eval is a method to execute a Python expression and return the evaluated value as a &PyAny object.

use pyo3::prelude::*;
use pyo3::types::IntoPyDict;

fn main() -> Result<(), ()> {
    let gil = Python::acquire_gil();
    let py = gil.python();
    let result = py.eval("[i * 10 for i in range(5)]", None, None).map_err(|e| {
        e.print_and_set_sys_last_vars(py);
    })?;
    let res: Vec<i64> = result.extract().unwrap();
    assert_eq!(res, vec![0, 10, 20, 30, 40]);
    Ok(())
}

Want to run statements? Then use run.

Python::run is a method to execute one or more Python statements. This method returns nothing (like any Python statement), but you can get access to manipulated objects via the locals dict.

You can also use the py_run! macro, which is a shorthand for Python::run. Since py_run! panics on exceptions, we recommend you use this macro only for quickly testing your Python extensions.

use pyo3::prelude::*;
use pyo3::{PyCell, PyObjectProtocol, py_run};
#  fn main() {
#[pyclass]
struct UserData {
    id: u32,
    name: String,
}
#[pymethods]
impl UserData {
    fn as_tuple(&self) -> (u32, String) {
        (self.id, self.name.clone())
    }
}
#[pyproto]
impl PyObjectProtocol for UserData {
    fn __repr__(&self) -> PyResult<String> {
        Ok(format!("User {}(id: {})", self.name, self.id))
    }
}
let gil = Python::acquire_gil();
let py = gil.python();
let userdata = UserData {
    id: 34,
    name: "Yu".to_string(),
};
let userdata = PyCell::new(py, userdata).unwrap();
let userdata_as_tuple = (34, "Yu");
py_run!(py, userdata userdata_as_tuple, r#"
assert repr(userdata) == "User Yu(id: 34)"
assert userdata.as_tuple() == userdata_as_tuple
"#);
# }

You have a Python file or Python function? Then use PyModule.

PyModule also can execute Python code by calling its methods.

use pyo3::{prelude::*, types::{IntoPyDict, PyModule}};
#  fn main() -> PyResult<()> {
let gil = Python::acquire_gil();
let py = gil.python();
let activators = PyModule::from_code(py, r#"
def relu(x):
    """see https://en.wikipedia.org/wiki/Rectifier_(neural_networks)"""
    return max(0.0, x)

def leaky_relu(x, slope=0.01):
    return x if x >= 0 else x * slope
"#, "activators.py", "activators")?;

let relu_result: f64 = activators.call1("relu", (-1.0,))?.extract()?;
assert_eq!(relu_result, 0.0);

let kwargs = [("slope", 0.2)].into_py_dict(py);
let lrelu_result: f64 = activators
    .call("leaky_relu", (-1.0,), Some(kwargs))?
    .extract()?;
assert_eq!(lrelu_result, -0.2);
# Ok(()) }