from PyQt4.Qt import *
import sys

class BaseClass(QObject):

    def __init__(self):
        super(BaseClass, self).__init__()
        print 'BaseClass.__init__'

    @pyqtSlot()
    def baseSlot(self):
        print 'baseSlot called :)'

class MainWindow(QMainWindow, BaseClass):
    def __init__(self, *args):
        super(MainWindow, self).__init__(*args)
        self.btn1 = QPushButton("Click me", self)
        #self.btn1.clicked.connect(self.baseSlot)

class App(QApplication):
    def __init__(self, *args):
        super(App, self).__init__(*args)
        self.main = MainWindow()
        self.main.show()

app = App(sys.argv)
app.exec_()