Bundling Python inside an Electron app

For Datasette Desktop I chose to bundle a full version of Python 3.9 inside my Datasette.app application. I did this in order to support installation of plugins via pip install - you can read more about my reasoning in Datasette Desktop—a macOS desktop application for Datasette.

I used python-build-standalone for this, which provides a version of Python that is designed for easy of bundling - it's also used by PyOxidize. Both projects are created and maintained by Gregory Szorc.

In development mode

In my Electron app's root folder I ran the following:

wget https://github.com/indygreg/python-build-standalone/releases/download/20210724/cpython-3.9.6-x86_64-apple-darwin-install_only-20210724T1424.tar.gz
tar -xzvf cpython-3.9.6-x86_64-apple-darwin-install_only-20210724T1424.tar.gz

This gave me a python/ subfolder containing a full standalone Python, ready to run on my Mac.

Running python/bin/python3.9 --version confirms that this is working correctly.

Calling Python from Electron

I used the Node.js child_process.execFile() function to execute Python scripts from inside Electron, like this:

const cp = require("child_process");
const util = require("util");
const execFile = util.promisify(cp.execFile);

await execFile(path_to_python, ["-m", "random"]);

path_to_python needs to be the path to that python3.9 executable. I wrote a findPython() function to find that, like so:

const fs = require("fs");

function findPython() {
  const possibilities = [
    // In packaged app
    path.join(process.resourcesPath, "python", "bin", "python3.9"),
    // In development
    path.join(__dirname, "python", "bin", "python3.9"),
  ];
  for (const path of possibilities) {
    if (fs.existsSync(path)) {
      return path;
    }
  }
  console.log("Could not find python3, checked", possibilities);
  app.quit();
}

The resourcesPath bit here works for the packaged and deployed application.

Packaging the app

I needed that python folder to be bundled up as part of the Datasette.app application bundle. I achieved that by adding the following to my "build" section in package.json:

    "extraResources": [
      {
        "from": "python",
        "to": "python",
        "filter": [
          "**/*"
        ]
      }
    ]

This causes electron-builder to copy the contents of that python folder into Datasette.app/Contents/Resources/python in the packaged application.

My findPython() function earlier knows to look for it there by creating a path to it starting with process.resourcesPath.

Signing and notarizing

I wrote extensive notes on signing and notarizing in Signing and notarizing an Electron app for distribution using GitHub Actions, which includes details on how I signed the Python binaries that ended up included in the package due to this pattern.

Created 2021-09-08T16:38:57-07:00 · Edit