How can I access Python code from JavaScript in PyQT 5.7?

Question

I used to do it by attaching an object

self.page().mainFrame().addToJavaScriptWindowObject("js_interface", self.jsi)

In 5.7 I do:

self.page().setWebChannel(self.jsi)

But I understandibly get a JavaScript error when I try to access exposed functions:

js: Uncaught ReferenceError: js_interface is not defined

Googling around I found that I should use qwebchannel.js, but I couldn't find the file or instructions on how to use it anywhere (there was some info, but only in some examples provided when installing QT, not PyQT).

Answer 1

You can include qwebchannel.js into html page using the script tag:

<script src="qrc:///qtwebchannel/qwebchannel.js"></script>

Then, create a web channel on the python side:

from PyQt5.QtCore import QObject, pyqtSlot
from PyQt5.QtWebChannel import QWebChannel
from PyQt5.QtWebEngineWidgets import QWebEngineView

class CallHandler(QObject):
    @pyqtSlot()
    def test(self):
        print('call received')

view = QWebEngineView()
channel = QWebChannel()
handler = CallHandler()
channel.registerObject('handler', handler)
view.page().setWebChannel(channel)

JS code that interacts with the web channel:

new QWebChannel(qt.webChannelTransport, function (channel) {
    window.handler = channel.objects.handler;
    window.handler.test();
});

Answer 2

Take a look at this page . It contains a useful example (in c++ but easily translatable into python).

First of all, you have to use a websocket to communicate from html to your app and viceversa.

Then you can set up your QWebChannel.

Answer 3

I think it's big drawback, JS cannot directly communicate with Python in PyQT5.9+ like it used to with "addToJavaScriptWindowObject" command. And using websockets... what if Firewall is heavy and all ports blocked.

I guess I will rely on simple callback (long pooling type from Python to JS checking for changes/commands) method and no QTWebChannel usage.