pyo3 0.3.1

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Rust bindings for the Python interpreter. This includes running and interacting with python code from a rust binaries as well as writing native python modules.

A comparison with rust-cpython can be found in the guide.


Pyo3 supports python 2.7 as well as python 3.5 and up. The minimum required rust version is 1.27.0-nightly 2018-05-01.

From a rust binary

To use pyo3, add this to your Cargo.toml:

pyo3 = "0.2"

Example program displaying the value of sys.version:

#![feature(use_extern_macros, specialization)]

extern crate pyo3;

use pyo3::prelude::*;

fn main() -> PyResult<()> {
    let gil = Python::acquire_gil();
    let py = gil.python();
    let sys = py.import("sys")?;
    let version: String = sys.get("version")?.extract()?;

    let locals = PyDict::new(py);
    locals.set_item("os", py.import("os")?)?;
    let user: String = py.eval("os.getenv('USER') or os.getenv('USERNAME')", None, Some(&locals))?.extract()?;

    println!("Hello {}, I'm Python {}", user, version);

As native module

Pyo3 can be used to generate a python-compatible library.


name = "rust2py"
version = "0.1.0"

name = "rust2py"
crate-type = ["cdylib"]

version = "0.2"
features = ["extension-module"]


#![feature(use_extern_macros, specialization)]

extern crate pyo3;
use pyo3::prelude::*;

// Add bindings to the generated python module
// N.B: names: "librust2py" must be the name of the `.so` or `.pyd` file
/// This module is implemented in Rust.
fn rust2py(py: Python, m: &PyModule) -> PyResult<()> {

    #[pyfn(m, "sum_as_string")]
    // ``#[pyfn()]` converts the arguments from Python objects to Rust values
    // and the Rust return value back into a Python object.
    fn sum_as_string_py(a:i64, b:i64) -> PyResult<String> {
       let out = sum_as_string(a, b);


// The logic can be implemented as a normal rust function
fn sum_as_string(a:i64, b:i64) -> String {
    format!("{}", a + b).to_string()

On windows and linux, you can build normally with cargo build --release. On Mac Os, you need to set additional linker arguments. One option is to compile with cargo rustc --release -- -C link-arg=-undefined -C link-arg=dynamic_lookup, the other is to create a .cargo/config with the following content:

rustflags = [
  "-C", "link-arg=-undefined",
  "-C", "link-arg=dynamic_lookup",

Also on macOS, you will need to rename the output from *.dylib to *.so. On Windows, you will need to rename the output from *.dll to *.pyd.

setuptools-rust can be used to generate a python package and includes the commands above by default. See examples/word-count and the associated


PyO3 is licensed under the Apache-2.0 license. Python is licensed under the Python License.