Usage Setup ⚙️:

Definition 1: Business Logic / A python project / Backend 🐍

Whatever you call for this step, it is just a regular Qt (PySide6) powered python project, which can take the advantage of full power of python with no limitation. To simplify the discussion here, it uses web socket(s) for real time communication and exposes objects through web socket(s). The properties, methods, signal/notifiers immediately become available to the UI with complete signature and type checking through type-script interfaces. Don’t worry about complicated processes for managing sockets, it is not your responsibility. This is handled automatically, you can simply focus on your project.

Definition 2: User Interface / A web project / Frontend 💻

Similarly, it is just a regular web project, which exploit the available modern UI tools. There is no limitation such as magically manipulated window interfaces or any complicated middle-ware translator which limits the functionality web library of yours.

`Step 1`: Create a meaningful directory structure.

It is completely up to you. But having a meaningful directory structure could make things simpler. For that purpose suggested way is to create a root directory with your AppName and two folders under the root directory, backend and frontend. As names suggest, they will be holding your python project as backend and UI project as frontend.

📦AppName
 ┣ 📂backend
 ┃  ┣ ...
 ┣ 📂frontend
 ┃  ┣ ...
 ┣ 📜README.md
 ┣ 📜LICENSE
 ┣ 📜.gitignore

Optinal virtual environment: If you prefer using virtual environment for your python projects (which is the suggested way for any python project), create one virtual environment, and use it under your backend folder.

`Step 2`: Install the library `pywebchannel`

pip install pywebchannel

`Step 3`: Create an entry point for your `backend`.

Add a main file with any name, i.e. main.py, inside your backend folder. The entry point will contain python main function and will create a QApplication and run it. The responsibility of the entry point is to initiate the WebChannelService object(s) (Yes, you read it right, it is plural, you can create more than one communication channels to your UI application, for different purposes). Addition to that main needs to create the object(s) (at least the ones which need to be available at the beginning), and register those object(s) to the related WebChannelService.

# main.py
import sys
from PySide6.QtWidgets import QApplication

from pywebchannel import WebChannelService

if __name__ == "__main__":
    app = QApplication(sys.argv)

    # Create a WebChannelService with a desired serviceName and the parent QObject
    commandTransferService = WebChannelService("Command Transfer Service", app)
    # Start the service with a desired port number, 9000 in this example
    commandTransferService.start(9000)

    ...
    ...
    ...

    app.exec()

`Step 4`: Create a python package

To hold classes which contains functionalities to be invoked from frontend. Typically, it is better to create two packages, one for functionality classes and one for fixed structured objects, even though the second one is optional, it is completely okay to create it, no harm will be done if it is empty. The names of these folders could be anything, but having meaningful names would be helpful. Let’s call them controllers, models respectively.

📦AppName
 ┣ 📂backend
 ┃  ┣ 📂controllers
 ┃  ┃  ┣ 🐍__init__.py
 ┃  ┣ 📂models
 ┃  ┃  ┣ 🐍__init__.py
 ┣ 📂frontend
 ┃  ┣ ...
 ┣ 🐍main.py
 ┣ 📜README.md
 ┣ 📜LICENSE
 ┣ 📜.gitignore

`Step 5`: Create a controller class under your `controllers` package.

This is going to be one of the Type you are going to expose to your UI. Let’s call it HelloWorldController. And make this class derived from Controller, which is imported from pywebchannel. Then, in your main, create an instance of it and register it into the WebChannelService.

# controllers/HelloWorldController.py
from typing import Optional
from PySide6.QtCore import QObject
from pywebchannel import Controller


# Create a Controller class
class HelloWorldController(Controller):
    def __init__(self, parent: Optional[QObject] = None):
        # Controller name is typically the name of the class '__name__' attribute could be used as well
        super().__init__("HelloWorldController", parent)

And in main:

# main.py
import sys
from PySide6.QtWidgets import QApplication
from pywebchannel import WebChannelService
from controllers.HelloWorldController import HelloWorldController

if __name__ == "__main__":
    app = QApplication(sys.argv)
    commandTransferService = WebChannelService("Command Transfer Service", app)
    commandTransferService.start(9000)

    # Create hello world controller object
    hwController = HelloWorldController(app)
    # Register controller for the communication service
    commandTransferService.registerController(hwController)

    app.exec()

`Step 6:` Add functionality

Technically, at this point our object, hwController has been already exposed to the any target UI. The functionality and properties of it is already accessible through a websocket located at port number 9000. The problem is that there is no functionality in our controller yet. Let’s add a method into our controller, and decorate this method with a decorator named Action imported from pywebchannel

# controllers/HelloWorldController.py
from typing import Optional
from PySide6.QtCore import QObject
from pywebchannel import Controller, Action


class HelloWorldController(Controller):
    def __init__(self, parent: Optional[QObject] = None):
        super().__init__("HelloWorldController", parent)

    # Create a class method and decorate it with @Action() decorator.
    # Don't forget to put annotations in your arguments. It is important!
    @Action()
    def sayHello(self, name: str):
        return f"Hello from 'HelloWorldController.sayHello' to my friend {name}"

`Step 7`: Create UI project

Now, we can try to use this inside a web app. For simplicity, inside the frontend, just create a Vite project with vanilla typescript template. You can create it yourself easily, or you can take it from examples folder.

`Step 8`: Establish connection

To establish connection between your backend and frontend, it is necessary to open a websocket connection from frontend to backend. Luckily, we can use built-in WebSocket in our frontend project. First create an api folder under your src and qwebchannel under that. Then populate the folder with given helpers in the repository examples (Just copy and paste the content into your project). Addition to those, you can create controllers and models directories as well, for nicely formatted structure.

📦AppName
 ┣ 📂backend
 ┃  ┣ 📂controllers
 ┃  ┃  ┣ 🐍__init__.py
 ┃  ┃  ┣ 🐍HelloWorldController.py
 ┃  ┣ 📂models
 ┃  ┃  ┣ 🐍__init__.py
 ┣ 📂frontend
 ┃  ┣ 📂node_modules 
 ┃  ┣ 📂public
 ┃  ┣ 📂src
 ┃  ┃  ┣ 📂api
 ┃  ┃  ┃  ┣ 📂controllers
 ┃  ┃  ┃  ┣ 📂models
 ┃  ┃  ┃  ┣ 📂qwebchannel
 ┃  ┃  ┃  ┃  ┣📜index.d.ts
 ┃  ┃  ┃  ┃  ┣📜index.js 
 ┃  ┃  ┣📜main.ts
 ┃  ┃  ┣📜vite-env-d.ts
 ┃  ┣📜index.html
 ┃  ┣📜package.json
 ┃  ┣📜tsconfig.json
 ┃  ┣📜.gitignore 
 ┣ 🐍main.py
 ┣ 📜README.md
 ┣ 📜LICENSE
 ┣ 📜.gitignore

`Step 9`: Add QWebChannel javascript interface

api/qwebchannel/index.js is the official QWebChannel javascript interface. However, it is different than the original (index_org.js) one. It has been updated to support async/await pattern instead of old-school callback style usage. Addition to that a typescript definition has been attached as well, index.d.ts.

`Step 10`: Websocket Helper

Now, create a class to handle the websocket communication boiler-plate. You can use given BaseAPI.ts and CommandAPI.ts from the repository. The important part here is the implementation of onChannelReady callback located under CommandAPI.ts. This is the part where you access your object exposed from backend . As you guess, this access will be storing the reference to that object inside our API object, so that we can use it whenever we need it. Update the CommandAPI.ts for learning purposed debugging

// Inside CommadAPI.ts copied from repository
export class CommandAPI extends BaseAPI {
  public constructor() {
    super("ws://localhost:9000", "Command Transfer Service");
  }

  // Update this part to see the channel content.
  async onChannelReady(channel: QWebChannel): Promise<void> {
    console.log(channel)
  }
}

Then add connection request into your main.ts

// main.ts
// import API
import {API} from "./api/CommandAPI.ts";

// Try to connect
API.connect().then(() => {
  if (API.isConnected()) {
    console.log("Successfully connected to backend")
  }
}).catch((error) => {
  console.log(error)
})

// Add a simple UI
document.querySelector<HTMLDivElement>('#app')!.innerHTML = `
  <div> 
    <input id="input">
    <button id="button">Say Hi</button>
  </div>
`

const input = document.querySelector<HTMLInputElement>('#input');
const button = document.querySelector<HTMLButtonElement>('#button');
button?.addEventListener('click', () => {
  console.log(input?.value)
})

`Step 11:` Run the projects

Now, run the backend project, and run the frontend project. If everything is correct, you should see an output from backend terminal:

[INFO] - Command Transfer Service: 'Command Transfer Service' is active at PORT=9000
[INFO] - Command Transfer Service: New Connection (Active client count: 1)

and something similar from frontend browser console.

QWebChannel {...}
Successfully connected to backend

When you expand the QWebChannel object on the console, you should see an objects and HelloWorldController inside it. If this is the case, you have successfully connected your python backend to your frontend

`Step 12`: Use it

Let’s use it and let our backend say hello to frontend. Just update your code as it should be:

Update CommandAPI.ts

export class CommandAPI extends BaseAPI {
  // Add an attribute for our API object
  HelloWorldController!: any;

  public constructor() {
    super("ws://localhost:9000", "Command Transfer Service");
  }

  async onChannelReady(channel: QWebChannel): Promise<void> {
    // Initialize it by the object located inside the QWebChannel
    this.HelloWorldController = channel.objects.HelloWorldController;
  }
}

Update main.ts

button?.addEventListener('click', async () => {
  // Call say hello with input value taken from input text box
  const response = await API.HelloWorldController.sayHello(input?.value)
  if (response.error) {
    // if an error occurred, display it
    console.log(response.error)
    return
  }

  if (response.success) {
    // if a success message has been received, display it
    alert(response.success)
    return
  }

  if (response.data) {
    // if an extra data has been received, display it
    alert(JSON.stringify(response.data))
    return
  }
})

Refresh your web page, and click the button. You should see an alert message saying Hello from 'HelloWorldController.sayHello' to my friend <your input value>

`Step 13`: Type hinting

Everything is ready to go. The ONLY MISSING part is type hint in our frontend, because we don’t have any type defintion for our controller, HelloWorldController. Type script generator given by pywebchannel comes in play at this moment.

Step 1: Copy ts_generator.py and Paste it into your backend root folder, same level with your main.py.
Step 2: Check the folder paths written in ts_generator.py script
Step 3: Run it in separate terminal.

python ts_generator.py

Step 4: You will see that the frontend controller folder will be populated with an auto generated Type-script interface, api/controllers/HelloWorldController.ts
Step 5: Since it needs to use Response interface for type-hinting for return values, it needs to be located inside api/models directory, which is not there yet. Please copy it from the repoository. And also copy the Signal interface as well, which is going to be necessary when you use signals.
Step 6: Now return back to your button.click listener implementation in main.ts. You will see that the function, sayHello(...), the return value response all are taking advantage of type-hinting.

`The last step`: Finalize your UI and serve it

When you complete your UI, you can serve it inside your backend project. For that purpose, you have a couple of options as usual.

First of all, you need to build your UI project. Inside your UI project, run:

npm run build

This is going to create a dist folder inside your UI project, frontend/dist. Copy dist folder into your backend project, and rename it with a meaningful name, such as app_ui.

Since it is a javascript based web project, opening the html file is not enough. The javascript functionalities will not be available. For that purpose, you need to serve it through a web server.

You can use the given HttpServer class inside pywebchannel for that purpose. It is a simple http server, which serves the given folder. Then you can access your UI through a browser, or even better, you can use QWebEngineView to display it

Please update your main.py file as follows. Feel free to use all the features you deserve from QWebEngineView:

# main.py
import sys

from PySide6.QtCore import QUrl
from PySide6.QtWebEngineCore import QWebEngineSettings
from PySide6.QtWebEngineWidgets import QWebEngineView
from PySide6.QtWidgets import QApplication

from controllers.HelloWorldController import HelloWorldController
from pywebchannel import WebChannelService, HttpServer

if __name__ == "__main__":
    app = QApplication(sys.argv)

    # Create a WebChannelService with a desired serviceName and the parent QObject
    commandTransferService = WebChannelService("Command Transfer Service", app)
    # Start the service with a desired port number, 9000 in this example
    commandTransferService.start(9000)

    # Create hello world controller object
    hwController = HelloWorldController(app)
    # Register controller for the communication service
    commandTransferService.registerController(hwController)

    # Create http server and start it
    UI_PORT = 12000
    httpServer = HttpServer("app_ui", UI_PORT, app)
    httpServer.start()

    # Website on QTGui
    view = QWebEngineView()
    view.settings().setAttribute(QWebEngineSettings.WebAttribute.PluginsEnabled, True)
    view.settings().setAttribute(QWebEngineSettings.WebAttribute.DnsPrefetchEnabled, True)
    view.load(QUrl(f"http://localhost:{UI_PORT}/"))
    view.setWindowTitle("Hello World App")
    view.show()

    app.exec()

This will spin a web server at port 12000, and serve the app_ui folder, and creates a QWebEngineView to display your UI. You can also access your UI through a browser by typing http://localhost:12000 into the address bar. This could be helpful, if you observe any weird behaviour on your UI. The console on the browser could be helpful to debug the problem.

Usage Setup ⚙️:

Definition 1: Business Logic / A python project / Backend 🐍

Definition 2: User Interface / A web project / Frontend 💻

Step 1: Create a meaningful directory structure.

Step 2: Install the library pywebchannel

Step 3: Create an entry point for your backend.

Step 4: Create a python package

Step 5: Create a controller class under your controllers package.

Step 6: Add functionality

Step 7: Create UI project

Step 8: Establish connection

Step 9: Add QWebChannel javascript interface

Step 10: Websocket Helper

Step 11: Run the projects

Step 12: Use it

Step 13: Type hinting

The last step: Finalize your UI and serve it