Python hatası

import sys
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
from PyQt5.QtWebEngineWidgets import *


class MainWindow(QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.browser = QWebEngineView()
        self.browser.setUrl(QUrl('http://google.com'))
        self.setCentralWidget(self.browser)
        self.showMaximized()

      
        navbar = QToolBar()
        self.addToolBar(navbar)

        geri_btn = QAction('geri', self)
        geri_btn.triggered.connect(self.browser.back)
        navbar.addAction(geri_btn)

        ileri_btn = QAction('ileri', self)
        ileri_btn.triggered.connect(self.browser.forward)
        navbar.addAction(ileri_btn)

        yuk_btn = QAction('yuk', self)
        yuk_btn.triggered.connect(self.browser.reload)
        navbar.addAction(yuk_btn)

        ev_btn = QAction('ev', self)
        ev_btn.triggered.connect(self.navigate_home)
        navbar.addAction(ev_btn)

        self.url_bar = QLineEdit()
        self.url_bar.returnPressed.connect(self.navigate_to_url)
        navbar.addWidget(self.url_bar)

        self.browser.urlChanged.connect(self.update_url)

    def navigate_home(self):
        self.browser.setUrl(QUrl('http://google.com'))

    def navigate_to_url(self):
        url = self.url_bar.text()
        self.browser.setUrl(QUrl(url))

    def update_url(self, q):
        self.url_bar.setText(q.toString())


app = QApplication(sys.argv)
QApplication.setApplicationName('EM Browser')
window = MainWindow()
app.exec_()