Using Pyodide

Pyodide may be used in any context where you want to run Python inside a web browser or a backend JavaScript environment.

Web browsers

To use Pyodide on a web page you need to load pyodide.js and initialize Pyodide with loadPyodide specifying an index URL for packages:

<!DOCTYPE html>
      <script src=""></script>
    <script type="text/javascript">
      async function main(){
        let pyodide = await loadPyodide({
          indexURL : ""
        console.log(pyodide.runPython("1 + 2"));

See the Getting started for a walk through tutorial as well as Loading packages and Type translations for a more in depth discussion about existing capabilities.

You can also use the Pyodide NPM package to integrate Pyodide into your application.


To avoid confusion, note that:

  • distributes Python packages built with Pyodide as well as pyodide.js

  • is a mirror of the Pyodide NPM package, which includes none of the WASM files

Supported browsers

Pyodide works in any modern web browser with WebAssembly support.

Tier 1 browsers are tested as part of the test suite with continuous integration,


Minimal supported version

Release date



22 October 2019



4 December 2018


Latest browser versions generally provide more reliable WebAssembly support and will run Pyodide faster, so their use is recommended.

Tier 2 browsers are known to work, but they are not systematically tested in Pyodide,


Minimal supported version

Release date



19 September 2019



26 Feb 2020

Other browsers with WebAssembly support might also work however they are not officially supported.

Web Workers

By default, WebAssembly runs in the main browser thread, and it can make UI non-responsive for long-running computations.

To avoid this situation, one solution is to run Pyodide in a WebWorker.


As of version 0.18.0 Pyodide can experimentally run in Node.js.

Install the Pyodide npm package,

npm install pyodide

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

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

let pyodide_pkg = await import("pyodide/pyodide.js");

let pyodide = await pyodide_pkg.loadPyodide({
  indexURL: "<pyodide artifacts folder>",

await pyodide.runPythonAsync("1+1");


To start Node.js REPL with support for top level await, use node --experimental-repl-await.


Download of packages from PyPI is currently not cached when run in Node.js. Packages will be re-downloaded each time micropip.install is run.

For this same reason, installing Pyodide packages from the CDN is explicitly not supported for now.