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).

xuhcc · Accepted Answer · 2017-03-11 20:31:48Z

12

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();
});

answered Mar 11, 2017 at 20:31

xuhcc

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2 Comments

devsnd Over a year ago

As addition: Please make sure that the channel, handler and so on are not garbage collected. I was initializing them in in class-method and I could not figure out why it did not work or even segfaulted. The trick was to keep a reference to channel and handler in the class (e.g. self.handler = CallHandler() etc

PankajKushwaha Over a year ago

@devsnd , I was getting Segmentation fault (core dumped) for weeks and I was nearly on verge of giving up on the project , you have not Idea how much your comment has helped me. Thank You!

JuanDeLosMuertos · Accepted Answer · 2016-09-20 12:11:01Z

1

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.

answered Sep 20, 2016 at 12:11

JuanDeLosMuertos

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Comments

Kiril · Accepted Answer · 2017-10-04 08:17:34Z

0

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.

answered Oct 4, 2017 at 8:17

Kiril

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