Я хочу использовать сочетания клавиш в своем коде в PyQt4

Я разрабатываю программу управления p-room. Когда пользователь нажимает клавишу «ESC», «диалог» завершается. Я хочу предотвратить это. Итак, я хочу использовать «второй код» в «первом коде».

from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_Dialog(object):
    def setupUi(self, Dialog):
        self.Dialog = Dialog
        self.Dialog.setObjectName(_fromUtf8("self.Dialog"))
        self.Dialog.resize(190, 98)
        self.pushButton = QtGui.QPushButton(self.Dialog)
        self.pushButton.setGeometry(QtCore.QRect(0, 0, 191, 101))
        font = QtGui.QFont()
        font.setPointSize(13)
        self.pushButton.setFont(font)
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        self.retranslateUi(self.Dialog)
        QtCore.QMetaObject.connectSlotsByName(self.Dialog)
        QtCore.QObject.connect(self.pushButton, QtCore.SIGNAL('released()'), self.Dialog.close) # <- put signal to close when clicked.

    def retranslateUi(self, Dialog):
        self.Dialog.setWindowTitle(_translate("self.Dialog", "self.Dialog", None))
        self.pushButton.setText(_translate("self.Dialog", "hi", None))

class QCustomDialog (QtGui.QDialog): # <- Implement your own
    def closeEvent(self, event):
        reply = QtGui.QMessageBox.question(self, 'Message',
            "Are you sure to quit?", QtGui.QMessageBox.Yes | 
            QtGui.QMessageBox.No, QtGui.QMessageBox.No)
        if reply == QtGui.QMessageBox.Yes:
            event.accept()
        else:
            event.ignore()

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    Dialog = QCustomDialog()
    ui = Ui_Dialog()
    ui.setupUi(Dialog)
    Dialog.show()
    sys.exit(app.exec_())

from PyQt4.Qt import Qt 
from PyQt4 import QtCore, QtGui
from PyQt4.QtCore import QObject, SIGNAL 
from PyQt4.QtGui import QWidget, QApplication, QMainWindow, QAction, QIcon, QKeySequence 
import os, time, MySQLdb, socket, sys


class MainWindow(QMainWindow): 
    def __init__(self, parent): 
        QMainWindow.__init__(self, parent) 
        self.centralwidget = QWidget(self) 

        self.action = QAction(QIcon(), "Down", self) 
        self.action.setShortcut("ESC") 
        self.action.setShortcutContext(Qt.ApplicationShortcut)
        self.addAction(self.action) 

        QObject.connect(self.action, SIGNAL("triggered()"), self.down) 

    def down(self): 
        print 'DOWN!!!' 

def main(): 
    app = QApplication(sys.argv) 
    mw = MainWindow(None) 
    mw.show() 
    sys.exit(app.exec_()) 

if __name__ == '__main__': 
    main()