QtDBus: how to call GetManagedObjects from bluez

[Alfalfa]

I want to list and extract all trusted bluetooth device by using QtDbus. With the qdbusviewer tool, I can see and call the method GetManagedObjects() just fine. Then I tried to do it in python, but the method cannot be found. The script below output ['Method "GetManagedObjects" with signature "" on interface "org.freedesktop.DBus.ObjectManager" doesn\'t exist']. What am I doing wrong?

#!/usr/bin/python3
import sys
from PyQt5 import QtWidgets, QtDBus

class Main(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        bus = QtDBus.QDBusConnection.systemBus()
        interface = QtDBus.QDBusInterface("org.bluez", "/org/bluez", "org.freedesktop.DBus.ObjectManager", bus)
        result = interface.call("GetManagedObjects")
        print(result.arguments())


if __name__== '__main__':
    app = QtWidgets.QApplication([])
    gui = Main()
    sys.exit(app.exec_())