14 unstable releases (3 breaking)

0.4.1 Aug 20, 2018
0.4.0 Jul 30, 2018
0.3.2 Jul 22, 2018
0.2.5 Feb 21, 2018
0.1.0 Jul 23, 2017

#14 in FFI

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Rust bindings for Python. 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 1.30.0-nightly 2018-08-18.

You can either write a native python module in rust or use python from a rust binary.

Using rust from python

Pyo3 can be used to generate a native python module.


name = "string-sum"
version = "0.1.0"

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

version = "0.4"
features = ["extension-module"]



extern crate pyo3;

use pyo3::prelude::*;

/// Formats the sum of two numbers as string
fn sum_as_string(a: usize, b: usize) -> PyResult<String> {
    Ok((a + b).to_string())

/// This module is a python moudle implemented in Rust.
fn string_sum(py: Python, m: &PyModule) -> PyResult<()> {


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",

For developing, you can copy and rename the shared library from the target folder: On mac os, rename libstring_sum.dylib to string_sum.so, on windows libstring_sum.dll to string_sum.pyd and on linux libstring_sum.so to libstring_sum.so. Then open a python shell in the same folder and you'll be able to import string_sum.

To build, test and publish your crate as python module, you can use pyo3-pack or setuptools-rust. You can find an example for setuptools-rust in examples/word-count, while pyo3-pack should work on your crate without any configuration.

Using python from rust

Add pyo3 this to your Cargo.toml:

pyo3 = "0.4"

Example program displaying the value of sys.version:


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);

Examples and tooling


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


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