PyO3

Rust bindings for Python. This includes running and interacting with Python code from a Rust binary, as well as writing native Python modules.

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

Usage

PyO3 supports Python 3.5 and up. The minimum required Rust version is 1.42.0-nightly 2019-01-21.

If you have never used nightly Rust, the official guide has a great section about installing it.

PyPy is also supported (via cpyext) for Python 3.5 only, targeted PyPy version is 7.0.0. Please refer to the pypy section.

You can either write a native Python module in Rust, or use Python from a Rust binary.

However, on some OSs, you need some additional packages. E.g. if you are on Ubuntu 18.04, please run

sudo apt install python3-dev python-dev

Using Rust from Python

PyO3 can be used to generate a native Python module.

Cargo.toml

[package]
name = "string-sum"
version = "0.1.0"
edition = "2018"

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

[dependencies.pyo3]
version = "0.9.1"
features = ["extension-module"]

src/lib.rs


#![allow(unused_variables)]
fn main() {
use pyo3::prelude::*;
use pyo3::wrap_pyfunction;

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

#[pymodule]
/// A Python module implemented in Rust.
fn string_sum(py: Python, m: &PyModule) -> PyResult<()> {
    m.add_wrapped(wrap_pyfunction!(sum_as_string))?;

    Ok(())
}
}

On Windows and Linux, you can build normally with cargo build --release. On macOS, 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:

[target.x86_64-apple-darwin]
rustflags = [
  "-C", "link-arg=-undefined",
  "-C", "link-arg=dynamic_lookup",
]

While developing, you can symlink (or copy) and rename the shared library from the target folder: On MacOS, rename libstring_sum.dylib to string_sum.so, on Windows libstring_sum.dll to string_sum.pyd, and on Linux libstring_sum.so to string_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 a Python module, you can use maturin or setuptools-rust. You can find an example for setuptools-rust in examples/word-count, while maturin should work on your crate without any configuration.

Using Python from Rust

If you want your Rust application to create a Python interpreter internally and use it to run Python code, add pyo3 to your Cargo.toml like this:

[dependencies]
pyo3 = "0.9.1"

Example program displaying the value of sys.version and the current user name:

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

fn main() -> Result<(), ()> {
    let gil = Python::acquire_gil();
    let py = gil.python();
    main_(py).map_err(|e| {
        // We can't display Python exceptions via std::fmt::Display,
        // so print the error here manually.
        e.print_and_set_sys_last_vars(py);
    })
}

fn main_(py: Python) -> PyResult<()> {
    let sys = py.import("sys")?;
    let version: String = sys.get("version")?.extract()?;
    let locals = [("os", py.import("os")?)].into_py_dict(py);
    let code = "os.getenv('USER') or os.getenv('USERNAME') or 'Unknown'";
    let user: String = py.eval(code, None, Some(&locals))?.extract()?;
    println!("Hello {}, I'm Python {}", user, version);
    Ok(())
}

Our guide has a section with lots of examples about this topic.

Examples and tooling

  • examples/word-count Counting the occurrences of a word in a text file
  • hyperjson A hyper-fast Python module for reading/writing JSON data using Rust's serde-json
  • rust-numpy Rust binding of NumPy C-API
  • html-py-ever Using html5ever through kuchiki to speed up html parsing and css-selecting.
  • pyo3-built Simple macro to expose metadata obtained with the built crate as a PyDict
  • point-process High level API for pointprocesses as a Python library
  • autopy A simple, cross-platform GUI automation library for Python and Rust.
    • Contains an example of building wheels on TravisCI and appveyor using cibuildwheel
  • orjson Fast Python JSON library
  • inline-python Inline Python code directly in your Rust code
  • Rogue-Gym Customizable rogue-like game for AI experiments
    • Contains an example of building wheels on Azure Pipelines
  • fastuuid Python bindings to Rust's UUID library
  • python-ext-wasm Python library to run WebAssembly binaries
  • dict-derive Derive FromPyObject to automatically transform Python dicts into Rust structs