[Python] PyQt5- setting button

import sys
from PyQt5.QtWidgets import QToolTip,QPushButton,QApplication, QHBoxLayout, QMainWindow, QPushButton, QWidget
from PyQt5.QtGui import QIcon,QFont

class TooltipForm(QMainWindow):
    def __init__(self):
        super(TooltipForm,self).__init__()
        self.initUI()
        self.button1.clicked.connect(self.onClick_Button)
    def initUI(self):
        self.setWindowTitle ( " first application main window " )
        self.setGeometry ( 200,200,300,300 )
         # status bar 
        self.status = self.statusBar ()
         # Icon 
        self.setWindowIcon (QIcon ( " ./image/lou.ico " ))   
         # set a button and displayed on the screen    
        self.button1 = QPushButton ()
        self.button1.setText ( " Button 1 " )
        self.button1.setToolTip ( " Button explained ." )
        layout = QHBoxLayout()
        layout.addWidget(self.button1)
            # Main frame, to place all controls of 
        the mainFrame = the QWidget ()
        mainFrame.setLayout(layout)
            # Make full screen 
        self.setCentralWidget (mainFrame)
     DEF onClick_Button (Self):
        SENDER = self.sender ()
         # used to determine whether an event is triggered, this refers to whether the button is pressed 
        App = QApplication.instance ()
         # exit the application 
        app.quit ()

if __name__ == "__main__":
    app = QApplication(sys.argv)
    main = TooltipForm ()
     # display window 
    main.show () 
     # established cycle 
    sys.exit (app.exec_ ())