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MIT license

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rust-cpython Build Status

Rust bindings for the python interpreter.

Copyright (c) 2015-2020 Daniel Grunwald. Rust-cpython is licensed under the MIT license. Python is licensed under the Python License.

Supported Python versions:

  • Python 2.7
  • Python 3.3 to 3.8

Requires Rust 1.30.0 or later.


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

cpython = "0.4"

Example program displaying the value of sys.version:

extern crate cpython;

use cpython::{Python, PyDict, PyResult};

fn main() {
    let gil = Python::acquire_gil();

fn hello(py: Python) -> PyResult<()> {
    let sys = py.import("sys")?;
    let version: String = sys.get(py, "version")?.extract(py)?;

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

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

Example library with python bindings:

The following two files will build with cargo build, and will generate a python-compatible library. On Mac OS, you will need to rename the output from *.dylib to *.so. On Windows, you will need to rename the output from *.dll to *.pyd.


At build time python3-sys/build.rs will look for interpreters in:

  • python
  • python3

picking the first one that works and is compatible with the configured expected version (by default, any Python 3.X interpreter will do). If a specific interpreter is desired, the PYTHON_SYS_EXECUTABLE environment variable should point to it.


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

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


#[macro_use] extern crate cpython;

use cpython::{PyResult, Python};

// add bindings to the generated python module
// N.B: names: "rust2py" must be the name of the `.so` or `.pyd` file
py_module_initializer!(rust2py, initrust2py, PyInit_rust2py, |py, m| {
    m.add(py, "__doc__", "This module is implemented in Rust.")?;
    m.add(py, "sum_as_string", py_fn!(py, sum_as_string_py(a: i64, b:i64)))?;

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

// rust-cpython aware function. All of our python interface could be
// declared in a separate module.
// Note that the py_fn!() macro automatically converts the arguments from
// Python objects to Rust values; and the Rust return value back into a Python object.
fn sum_as_string_py(_: Python, a:i64, b:i64) -> PyResult<String> {
    let out = sum_as_string(a, b);

On windows and linux, you can build normally with cargo build --release. On Mac Os, you need to set additional linker arguments. The simplest solution is to create a .cargo/config with the following content:

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

For setup.py integration, see https://github.com/fafhrd91/setuptools-rust