class PBTester(QtCore.QObject):
    ...
    def RunTasks(self):
        self.processStarted.emit(0, "Primary Task", 0, 1)
        self._runTask1()

    def _runTask1(self):
        self.processStarted.emit(1, "First Subtask", 0, 1000)
        for index in range(1000):
            self.processUpdated.emit(1, index)
        self.processCompleted.emit(1)

        QtCore.QTimer.singleShot(0, self._runTask2)

    def _runTask2(self):
        self.processStarted.emit(1, "Second Subtask", 0, 1000)
        for index in range(1000):
            self.processUpdated.emit(1, index)
        self.processCompleted.emit(1)

        self._tasksComplete()

    def _tasksComplete(self):
        self.processCompleted.emit(0)


class PBUI(QtGui.QMainWindow):
    ...
    def runTests(self):
        cObj = PBTester(self)
        cObj.processStarted.connect(self.addProgressBar)
        cObj.processUpdated.connect(self.updateProgressBar)
        cObj.processCompleted.connect(self.removeProgressBar)
        cObj.RunTasks()