rob-opsi / milksnake

A setuptools/wheel/cffi extension to embed a binary data in wheels

Milksnake

Milksnake is an extension for setuptools that allows you to distribute dynamic linked libraries in Python wheels in the most portable way imaginable.

It gives you a hook to invoke your own build process and to then take the resulting dynamic linked library.

Why?

There are already other projects that make Python and native libraries play along but this one is different. Unlike other projects that build Python extension modules the goal of this project is to build regular native libraries that are then loaded with CFFI at runtime. Why not just use CFFI? Because CFFI's setuptools support alone does not properly work with such wheels (it does not provide a way to build and properly tag wheels for shared libraries) and it does not provide a good way to invoke an external build process (like a makefile, cargo to build rust binaries etc.)

In particular you will most likely only need two wheels for Linux, one for macs and soon one for Windows independently of how many Python interpreters you want to target.

What is supported?

• Platforms: Linux, Mac, Windows
• setuptools commands: bdist_wheel, build, build_ext, develop
• pip install --editable .
• Universal wheels (PACKAGE-py2.py3-none-PLATFORM.whl); this can be disabled with milksnake_universal=False in setup() in case the package also contains stuff that does link against libpython.

How?

This example shows how to build a rust project with it:

This is what a setup.py file looks like:

from setuptools import setup

def build_native(spec):
    # build an example rust library
    build = spec.add_external_build(
        cmd=['cargo', 'build', '--release'],
        path='./rust'
    )

    spec.add_cffi_module(
        module_path='example._native',
        dylib=lambda: build.find_dylib('example', in_path='target/release'),
        header_filename=lambda: build.find_header('example.h', in_path='target'),
        rtld_flags=['NOW', 'NODELETE']
    )

setup(
    name='example',
    version='0.0.1',
    packages=['example'],
    zip_safe=False,
    platforms='any',
    setup_requires=['milksnake'],
    install_requires=['milksnake'],
    milksnake_tasks=[
        build_native
    ]
)

You then need a rust/ folder that has a Rust library (with a crate type of cdylib) and a example/ python package.

Example example/__init__.py file:

from example._native import ffi, lib


def test():
    return lib.a_function_from_rust()

And a rust/src/lib.rs:

#[no_mangle]
pub unsafe extern "C" fn a_function_from_rust() -> i32 {
    42
}

And the rust/Cargo.toml:

[package]
name = "example"
version = "0.1.0"
build = "build.rs"

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

[build-dependencies]
cbindgen = "0.4"

And finally the build.rs file:

extern crate cbindgen;

use std::env;

fn main() {
    let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
    let mut config: cbindgen::Config = Default::default();
    config.language = cbindgen::Language::C;
    cbindgen::generate_with_config(&crate_dir, config)
      .unwrap()
      .write_to_file("target/example.h");
}