PyQT- TypeError: connect() failed between triggered(bool) and on_open()

Question

Now I'm doing graph cut project from this repository https://github.com/NathanZabriskie/GraphCut/tree/master And I try to execute the code from folder "graph_cut" file "NewCutUI.py"

import sys
import cv2
import numpy as np
from PyQt5.QtCore import pyqtSlot
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
import GraphMaker

class NewCutUI:

    def __init__(self):
        self.graph_maker = GraphMaker.GraphMaker()
        self.a = QApplication(sys.argv)
        self.window = QMainWindow()
        self.window.setWindowTitle("GraphCut")
        self.seed_num = self.graph_maker.foreground

        # Setup file menu
        mainMenu = self.window.menuBar()
        fileMenu = mainMenu.addMenu('&File')

        openButton = QAction(QIcon('exit24.png'), 'Open Image', self.window)
        openButton.setShortcut('Ctrl+O')
        openButton.setStatusTip('Open a file for segmenting.')
        openButton.triggered.connect(self.on_open) 
        fileMenu.addAction(openButton)

    @pyqtSlot()
    def on_open(self):
        f = QFileDialog.getOpenFileName()
        if f is not None:#and f != "":
            self.graph_maker.load_image(str(f))
            self.seedLabel.setPixmap(QPixmap.fromImage(
        self.get_qimage(self.graph_maker.get_image_with_overlay(self.graph_maker.seeds))))
            self.segmentLabel.setPixmap(QPixmap.fromImage(
                self.get_qimage(self.graph_maker.get_image_with_overlay(self.graph_maker.segmented))))

But when I execute, I got this error: TypeError: connect() failed between triggered(bool) and on_open()

How can i fixed it? here is repository that I got code from in file "NewCutUI.py" ref: https://github.com/NathanZabriskie/GraphCut/tree/master