gistfile1.py

import sys

from PySide.QtCore   import *
from PySide.QtGui    import *
from PySide.QtWebKit import *

class Everything(QObject):
    @Slot(result=int)
    def answer(self):
        return 42

app = QApplication(sys.argv)
web = QWebView()
web.load(QUrl("http://www.example.com/"))
web.show()
frame = web.page().mainFrame()
frame.addToJavaScriptWindowObject("Everything", Everything())
frame.evaluateJavaScript("alert(Everything.answer())") # It alerts 0 instead of 42

sys.exit(app.exec_())