Simple example of getting the rust-cpython and setuptools-rust examples working together

__init__.py

# hello_rust/__init__.py just needs to exist and not be invalid Python

__main__.py

# hello_rust/__main__.py

from . import _helloworld

def main():
    print("Calculated with Rust: " + _helloworld.sum_as_string(1, 2))

# This allows main() to be called both via `python -m`
# and via setuptools entry points.
if __name__ == '__main__':
    main()

Cargo.toml

[package]
name = "unimportant_if_subsumed_by_setuptools"
version = "0.1.0"
authors = ["Your Name Here <your@email.com>"]

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

[dependencies.cpython]
version = "0.1"
default-features = false
features = ["python27-sys", "extension-module-2-7"]

# NOTE: If using Python 3, replace `default-features` and `features` lines with this:
# features = ["extension-module"]

justfile

# Clear out all built files
clean:
	cargo clean
	rm hello_rust/*.so hello_rust/*.pyc || true

# vim: set ft=make textwidth=100 colorcolumn=101 noexpandtab sw=8 sts=8 ts=8 :

lib.rs

// src/lib.rs

#[macro_use] extern crate cpython;

use cpython::{PyResult, Python};

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

// 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);
    Ok(out)
}

RUN_ME.sh

#!/bin/sh

# Playing things safe and allowing this to be used for testing changes to setup.py
deactivate
rm -rf venv

# The actual meat of the script
virtualenv venv &&
. ./venv/bin/activate &&
python setup.py develop
python -m hello_rust

setup.py

from setuptools import setup

# Workaround from https://github.com/PyO3/setuptools-rust/issues/2
try:
    from setuptools_rust import Binding, RustExtension
except ImportError:
    import os, subprocess, sys
    try:
        subprocess.check_call([sys.executable, '-m', 'pip',
                               'install', 'setuptools-rust'])
        os.execvp(sys.executable, [sys.executable] + sys.argv)
    except subprocess.CalledProcessError as err:
        print("Please install setuptools-rust package")
        raise SystemExit(err.errno)

setup(name='hello-rust',
      version='1.0',
      rust_extensions=[RustExtension('hello_rust._helloworld',
                                     'Cargo.toml',
                                     binding=Binding.RustCPython)],
      packages=['hello_rust'],
      # rust extensions are not zip safe, just like C-extensions.
      zip_safe=False)