class ThreadsApp(QtWidgets.QMainWindow):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        self.ui = uic.loadUi('changer.ui', self)
        self.thread = {}
        self.pushButton.clicked.connect(self.start_worker)
        self.pushButton_2.clicked.connect(self.stop_worker)

    def start_worker(self):
        self.thread[1] = ThreadClass(parent = None)
        self.thread[1].start()
        self.thread[1].signals.connect(self.go_while)

    def stop_worker(self):
        self.pushButton.setText("Start")
        self.thread[1].stop()

    def go_while(self):
        print('asasd')

class ThreadClass(QtCore.QThread):
    signals = QtCore.pyqtSignal(int)

    def __init__(self, parent = None):
        super(ThreadClass, self).__init__(parent)
        self.running = True

    def run(self):
        print('Start Thread')

    def stop(self):
        self.running = False
        print('Stop Thread')
        self.terminate()