pyodide

Pyodide JavaScript package

Usage

Download and extract Pyodide packages from Github releases (pyodide-build-*.tar.bz2). The version of the release needs to match exactly the version of this package.

Then you can load Pyodide in Node.js as follows,

// hello_python.js
const { loadPyodide } = require("pyodide");

async function hello_python() {
  let pyodide = await loadPyodide({
    indexURL: "<pyodide artifacts folder>",
  });
  return pyodide.runPythonAsync("1+1");
}

hello_python().then((result) => {
  console.log("Python says that 1+1 =", result);
});

$ node hello_python.js
Loading distutils
Loaded distutils
Python says that 1+1= 2

Or you can use the REPL. To start the Node.js REPL with support for top level await, use node --experimental-repl-await:

$ node --experimental-repl-await
Welcome to Node.js v18.5.0.
Type ".help" for more information.
> const { loadPyodide } = require("pyodide");
undefined
> let pyodide = await loadPyodide();
Loading distutils
Loaded distutils
undefined
> await pyodide.runPythonAsync("1+1");
2

Node.js versions <0.17

• Node.js versions 14.x and 16.x: to use certain features of Pyodide you need to manually install node-fetch, e.g. by doing npm install node-fetch.

• Node.js v14.x: you need to pass the option --experimental-wasm-bigint when starting Node. Note that this flag is not documented by node --help and moreover, if you pass --experimental-wasm-bigint to node >14 it is an error:

$ node -v
v14.20.0

$ node --experimental-wasm-bigint hello_python.js
warning: no blob constructor, cannot create blobs with mimetypes
warning: no BlobBuilder
Loading distutils
Loaded distutils
Python says that 1+1= 2

See the documentation fore more details.

Details

The JavaScript code in this package is responsible for the following tasks:

1. Defines the public JavaScript API
   • Package loading code to allow loading of other Python packages.
   • Can load micropip to bootstrap loading of pure Python wheels
2. Loads the CPython interpreter and the core/pyodide emscripten application which embeds the interpreter.
3. Injects the js/pyodide JavaScript API into sys.modules. This is the final runtime dependency for core/pyodide & py/pyodide, so after this step the interpreter is fully up and running.