Electron-Flask Integration Project #2

date

Jun 16, 2023

slug

electron-flask-integration-2

author

status

Public

Start your Flask Server in Virtual Environment

example-code-2

changjoon-park • Updated Jun 20, 2023

It is possible to start your Flask server in its virtual environment using Electron's child_process module. The child_process module enables us to spawn child processes in Node.js, and we can use it to activate our virtual environment and then run our Flask application.


const { app, BrowserWindow } = require('electron')
const path = require('path');
const { spawn } = require('child_process');

function createWindow () {
  const win = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      nodeIntegration: true,
    }
  })

  win.loadFile('index.html')

  // Path to Python venv
  const venvPath = path.join(__dirname, '..', 'server', '.venv', 'Scripts', 'python.exe');

  // Path to Flask application
  const flaskAppPath = path.join(__dirname, '..', 'server', 'app.py');

  // Start Flask server
  const flaskServer = spawn(venvPath, [flaskAppPath]);

  flaskServer.stdout.on('data', (data) => {
    console.log(`stdout: ${data}`);
  });

  flaskServer.stderr.on('data', (data) => {
    console.error(`stderr: ${data}`);
  });

  flaskServer.on('close', (code) => {
    console.log(`Flask server exited with code ${code}`);
  });
}

app.whenReady().then(createWindow)

electron-flask-example-2\main.js

This code uses the spawn() function to start a new process with the Python interpreter in the virtual environment and the path to the Flask app as arguments. spawn() returns a ChildProcess instance, which we can use to listen for output (stdout) and errors (stderr) from the Flask server and when the server process exits (close).

This code assumes your Electron app is in a sibling directory to your server directory, and that the server directory contains your virtual environment and your Flask app. You may need to adjust the paths in this code depending on your project structure.

Please note that this code is for Windows systems, where Python virtual environments have a Scripts directory. On Unix or MacOS systems, you would need to activate the environment and run the server using the bin directory instead. Also, you'll need to handle shutting down the Flask server when your Electron app closes, and handle other lifecycle events as needed.

In the code provided, we use Node.js's child_process module to spawn a new process, which is used to run the Flask server from Electron.


// Path to Python venv
const venvPath = path.join(__dirname, '..', 'server', '.venv', 'Scripts', 'python.exe');

This line creates a string representing the path to the Python executable in your virtual environment. The __dirname variable is a global variable in Node.js that gives the directory of the current module (in this case, the directory where your main.js file is located). We use the path.join() function to combine this with the relative path to your virtual environment's Python executable.


// Path to Flask application
const flaskAppPath = path.join(__dirname, '..', 'server', 'app.py');

This line creates a string representing the path to your Flask application file. It works similarly to the previous line.


// Start Flask server
const flaskServer = spawn(venvPath, [flaskAppPath]);

This line starts the Flask server. The spawn() function creates a new process with the command given by the first argument (venvPath, the path to the Python executable in the virtual environment), and any command line arguments given by the second argument (an array containing flaskAppPath, the path to your Flask application file).

The spawn() function returns a ChildProcess object, which we store in the flaskServer variable. This object can be used to interact with the new process.


flaskServer.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);
});

This block of code sets up a listener for the data event on the stdout (standard output) stream of the new process. When the process writes to stdout (for example, if your Flask server prints a message when it starts), this event will be fired, and the provided callback function will be called with the data that was written. In this case, the callback function simply logs the data to the console.


flaskServer.stderr.on('data', (data) => {
  console.error(`stderr: ${data}`);
});

This block of code does the same thing, but for the stderr (standard error) stream of the new process. If the process writes to stderr (for example, if an error occurs in your Flask server), this event will be fired, and the provided callback function will be called with the error message. This callback function logs the error to the console using console.error().


flaskServer.on('close', (code) => {
  console.log(`Flask server exited with code ${code}`);
});

This block of code sets up a listener for the close event on the ChildProcess object. This event is fired when the new process exits (either because it finished running or because an error occurred). The provided callback function is called with the exit code of the process, and it logs a message to the console to indicate that the Flask server has exited and provides the exit code.

So in short, this code starts your Flask server as a new process, and sets up listeners to handle output from the server, errors, and when the server process exits. This way, you can see what's happening with the Flask server while your Electron app is running.

Electron-Flask Integration Project #2

Start your Flask Server in Virtual Environment

Summary