[PyQt] How to process QDBusPendingCallWatcher results?

[Evade Flow]

I'm working on an app that needs to invoke methods in
various D-Bus services asynchronously, so I wrote this small program to
test the basic machinery:


   from PyQt4 import QtCore, QtDBus

   class DeviceInterface(QtDBus.QDBusAbstractInterface):

       def __init__(self, service, path, connection, parent=None):
           super().__init__(service, path,
                            'org.freedesktop.UDisks.Device',
                            connection, parent)

       @QtCore.pyqtSlot(QtDBus.QDBusArgument)
       def callFinishedSlot(self, arg):
           print("Got result:", arg)


   if __name__ == '__main__':
       import sys
       app = QtCore.QCoreApplication(sys.argv)

       dev = DeviceInterface('org.freedesktop.UDisks.Device',
                             '/org/freedesktop/UDisks/Device/sda1',
                             QtDBus.QDBusConnection.systemBus(), app)

       async = dev.asyncCall("FilesystemListOpenFiles");
       watcher = QtDBus.QDBusPendingCallWatcher(async, dev)
       watcher.finished.connect(dev.callFinishedSlot)
       sys.exit(app.exec_())


It seems to work(?) Anyway, it prints:

   Got result: <PyQt4.QtDBus.QDBusPendingCallWatcher object at 0xb740c77c>

The trouble is, I can't figure out how to get results out of the
QDBusPendingCallWatcher object.  The C++ code I adapted the above
example from does this:

    void MyClass.callFinishedSlot(QDBusPendingCallWatcher *call)
    {
        QDBusPendingReply<QString, QByteArray> reply = *call;
        if (reply.isError()) {
            showError();
        } else {
            QString text = reply.argumentAt<0>();
            QByteArray data = reply.argumentAt<1>();
            showReply(text, data);
        }
        call->deleteLater();
    }

Can anyone suggest how I might convert the C++ slot syntax to something
that will work with PyQt?  Thanks!