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build_ext for Pyodide

Project description

exodide: build_ext for Pyodide


1. Overview

Pyodide is a WebAssembly variant of CPython. By using it, we can run Python code inside web browser.

Although we can run most of pure-Python packages on Pyodide, however, available C/C++ extension packages are limited to builtin packages. (Update: From v0.21.0, Pyodide started to accept non-builtin C/C++ packages.)

The motivation of this project (exodide) is providing C/C++ extension builder for Pyodide, and enables users to run your own custom C/C++ extension packages on Pyodide.

2. Usage

2.1 Requirement Summary

  • 2.3: Build
  • 2.4: Run
    • Pyodide v0.21.0
  • 2.5: Inspect

2.2 Install exodide

2.2.1 Install from PyPI

You can install exodide from PyPI

  • pip install exodide
  • pip install exodide[build]
    • With build dependencies
  • pip install exodide[inspect]
    • With inspect dependencies
  • pip install exodide[all]
    • With all dependencies

2.2.2 Use docker image

We provide docker image

docker run -it -v <your package source path>:/src bash

# Inside docker container
source /emsdk/ # Set PATH for emcc/em++

2.2.3 Install from Source

Since this repository doesn't contains patched headers, you cannot install directly from GitHub like pip install git+

git clone --recursive --depth 1
cd exodide


pip install .

2.3 Build with exodide

The followings are reuired;

  • Emscripten v3.1.14
  • C/C++ extension package source working on Python 3.10
  • wheel (pip install exodide[build] install it, too.)

2.3.1 Method 1: Main Usage

from setuptools import setup
from exodide import build

# omit

    # omit
    cmdclass=build.cmdclass(), # {'build':, 'build_ext': build.build_ext}

then CC=emcc CXX=em++ python bdist_wheel.

2.3.2 Method 2: Fine tuning for Power User

If your package has special build flow, you might need to call exodide internal API.

All internal build API are implemented at module.

  • system_include() -> str: System include directory of host Python
  • exodide_include() -> List[str]: Include directories inside exodide package.
  • adjust_include(include: List[str]) -> List[str]: Adjust include directories
    • Internally system_include() and exodide_include() are used
  • exodide_links() -> List[str]: Linker arguments
  • exodide_unsupported_links() -> List[str]: Unsupported linker arguments
  • exodide_platform_tag() -> str: Platform name tag for wheel

2.3.3 Method 3: Quick Usage

We also provide custom setup command exodide_wheel. The following command have same effect with the first option at '2.3.1 Main Usage'.

CC=emcc CXX=em++ python --command-packages exodide exodide_wheel

2.3.4 Notes

Pyodide doesn't provide all the functionalities of CPython, so that you might need to modify your package. You can detect Emscripten compiler by __EMSCRIPTEN__ macro (ref).

#ifdef __EMSCRIPTEN__
// Code for Pyodide
// Code for Others

2.4 Install extension package to Pyodide

Note Since from Pyodide v0.21.0 micropip.install() accepts custom URL, exodide.install module become deprecated.

Pyodide v0.21 is required.

const pyodide = await loadPyodide();

await pyodide.runPythonAsync(`
import micropip

import your_package
# omit

2.5 Inspect Shared Object (for Debugging)

Fot inspect, numpy is also required, and you can install with pip install exodide[inspect].

python3 -m exodide.inspect your-package/

Currently, exodide.inspect module prints dylink / dylink.0 custom section, which are used for metadata of Wasm dynamic link.


We utilize other projects and these codes obey their original lisences. We distribute patched header files of CPython and NumPy, too.

4. Technical Details

Technical details are described here

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