pywebchannel 1.0

This repository generates auto typescript files for QWebChannel python local backend. It enables you to build a stunning UI for your python project with web technologies.

Python Web Channel 🚀

pywebchannel is a tool that automatically generates TypeScript files for QWebChannel Python local backend. It allows you to create a stunning UI for your Python project using web technologies such as HTML, CSS, and JavaScript.

With pywebchannel, you can:

• Write your backend logic in Python and use Qt (PySide6) for communication.
• Use QWebChannel to communicate with the web frontend and expose your Python objects and methods.
• Write your frontend UI in any web framework of your choice, such as vanilla JS, React, Solid, Vue, etc.
• Enjoy the benefits of TypeScript, such as type safety, code completion, and error detection.
• Save time and effort by automatically generating TypeScript interfaces from your Python code.

Type-Script Generator ⚙️

The TypeScript Generator part of this library has a file watcher that translates Python code to TypeScript interfaces. This enables safe and easy communication between your Python backend and your desired frontend (vanilla JS, React, Solid, Vue, etc.). To use the TypeScript Generator, run the ts_generator.py script and specify the folders that contain the Python files you would like watch for auto-instant conversion.

Controller Utilities

pywebchannel provides helpful classes, functions and decorators to generate proper controller classes which can be exposed to a UI written by using web technologies. All given types are self documented and easy to follow.

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

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• 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: 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: 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.

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• Step 8: 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 
 ┃  ┃  ┃  ┃  ┣📜reeadme.txt
 ┃  ┃  ┣📜main.ts
 ┃  ┃  ┣📜vite-env-d.ts
 ┃  ┣📜index.html
 ┃  ┣📜package.json
 ┃  ┣📜tsconfig.json
 ┃  ┣📜.gitignore 
 ┣ 🐍main.py
 ┣ 📜README.md
 ┣ 📜LICENSE
 ┣ 📜.gitignore

---

• Step 9: 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. In order to enable this in your project just import it through your index.html at the head section with script tag

<script type="text/javascript" src="src/qwebchannel"></script>

---

• Step 10: 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
await API.connect()

// Inform about connection
if (API.isConnected()) {
  console.log("Successfully connected to backend")
}

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)
})

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• Step 11: 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: 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
  }
})

---

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.
• Step 4: You will see that the 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.

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🎊🎈✌️ Congratulations!!! 🎊🎈✌️

You have successfully connected your python backend to your frontend. And started a tool application which is capable of generating typescript interfaces you need, by just watching changes in your backend.

As long as you keep these tool active and running, it will update all the scripts automatically while you are changing your backend implementation, so your frontend will be up-to-date

Now, you can check other examples and self-explained api. Good luck on combining best of two worls.

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How to Contribute 🙌

If you want to contribute to this project, you are more than welcome. Here are some ways you can help:

• Report any bugs or issues you find.
• Suggest new features or improvements.
• Submit pull requests with your code changes.
• Share your feedback or suggestions.

License 📄

This project is licensed under the MIT License. See the LICENSE file for details.

Credits 🙏

This project was inspired by the following sources:

• QWebChannel - a Qt module that enables seamless integration of C++ and HTML/JavaScript.
• PySide6 - a Python binding of the cross-platform GUI toolkit Qt.
• Solid - a declarative JavaScript library for building user interfaces.
• TypeScript - a superset of JavaScript that adds optional types.

Thank you for your interest in pywebchannel. I hope you enjoy using it as much as I enjoyed creating it. 😊