Question

QtWebkit segfaults whenever I return a QObject from a method of another QObject.

Here’s the simplest test case that I can come up with (it works for both PySide and PyQt4):

#!/usr/bin/env python2

import sys

try:
  from PyQt4.QtCore import QObject, QVariant, pyqtProperty
  from PyQt4.QtGui import QApplication
  from PyQt4.QtWebKit import QWebView

  Property = pyqtProperty
except ImportError:
  from PySide.QtCore import QObject, Property
  from PySide.QtGui import QApplication
  from PySide.QtWebKit import QWebView

class TestObject(QObject):
  @Property(str)
  def property(self):
    return 'foo'

class TestObjectContainer(QObject):
  @Property(QObject)  # Swapping QObject with TestObject doesn't fix it
  def object(self):
    return TestObject()

if __name__ == '__main__':
  application = QApplication(sys.argv)

  browser = QWebView()
  frame = browser.page().mainFrame()

  frame.addToJavaScriptWindowObject('container', TestObjectContainer())
  frame.addToJavaScriptWindowObject('test_object', TestObject())

  browser.show()

  #frame.evaluateJavaScript('test_object.property')
  frame.evaluateJavaScript('container.object.property')

  sys.exit(application.exec_())

Here is the odd part:

test_object.property;       // This doesn't segfault
container.object.property;  // This does

Is there any way to return QObjects like this? Am I doing something wrong, or is this a bug?

---

I ended up creating a simple wrapper class with the help of @HYRY’s answer:

class WebkitQObject(QObject):
  def __init__(self):
    super(WebkitQObject, self).__init__()
    self.__cache__ = []

  def store(self, item):
    self.__cache__.append(item)

    return self.__cache__[-1]

Now, this code works with a slight modification:

class TestObjectContainer(WebkitQObject):
  @Property(QObject)
  def object(self):
    return self.store(TestObject())

Answer 1

You need a Python reference to the QObject to keep it alive. You can test this by changing the code as following,

class TestObjectContainer(QObject):
  @Property(QObject)
  def object(self):
    self.tmp = TestObject()
    return self.tmp