I am working on a PyQt5 application that uses QWebEngineView, and I want to call a Python function from JavaScript. I found an example here, and I've implemented the code as follows:
main.py
from os.path import abspath, dirname, join
import sys
from PyQt5.QtCore import QUrl, pyqtSlot
from PyQt5.QtWebEngineWidgets import QWebEngineView, QWebEnginePage
from PyQt5.QtWidgets import QApplication, QMainWindow, QWidget, QVBoxLayout
from PyQt5.QtWebChannel import QWebChannel
HTML_PATH = join(dirname(abspath(__file__)), 'page.html')
class WebEngineView(QWebEngineView):
def __init__(self):
super().__init__()
@pyqtSlot()
def foo(self):
print('bar')
class MainWindow(QMainWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.browser = WebEngineView()
self.channel = QWebChannel()
self.channel.registerObject('backend', self.browser)
self.browser.page().setWebChannel(self.channel)
self.browser.setPage(WebEnginePage(self.browser))
url = QUrl.fromLocalFile(HTML_PATH)
self.browser.load(url)
central_widget = QWidget()
layout = QVBoxLayout(central_widget)
layout.addWidget(self.browser)
self.setCentralWidget(central_widget)
class WebEnginePage(QWebEnginePage):
def javaScriptConsoleMessage(self, level, message, lineNumber, sourceID):
print(f"[JS Message] Line-{lineNumber}:",message)
if __name__ == '__main__':
app = QApplication(sys.argv)
win = MainWindow()
win.showMaximized()
sys.exit(app.exec_())
page.html:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<script src="qrc:///qtwebchannel/qwebchannel.js"></script>
</head>
<body>
<h1>PyQt5 and QWebEngineView Example</h1>
<button onclick="callPython()">Call Python</button>
<script>
function callPython(){
backend.foo();
}
var backend;
new QWebChannel(qt.webChannelTransport, function (channel) {
backend = channel.objects.backend;
});
</script>
</body>
</html>
However, I am encountering the following error in my browser console:
Uncaught ReferenceError: qt is not defined
Python version 3.8.0, PyQt5==5.15.10, PyQtWebEngine==5.15.6
self.browser.setPage()beforeself.browser.page().setWebChannel(self.channel).Property 'X'' of object 'WebEngineView' has no notify signal and is not constant, value updates in HTML will be broken!warnings. What causes it?QtCore.qInstallMessageHandler(lambda *args: None)) or use a separate backend (subclassing QObject) and eventually implement proper signals to communicate with the view.