from PyQt5 import  QtCore,QtGui,QtWidgets,uic
import sys
class Test(QtWidgets.QMainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        Form, Base = uic.loadUiType('test.ui')
        self.ui = Form()
        self.ui.setupUi(self)
.................................................
 def keyPressEvent(self, e):
        if e.key == QtCore.Qt.Key_Alt:
            QtWidgets.QMessageBox.warning(self, "Quit", "Are not quit",
                                                   buttons=QtWidgets.QMessageBox.Cancel,
                                                   defaultButton=QtWidgets.QMessageBox.Cancel)
if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    Test = Test()
    sys.exit(app.exec())

 if e.key() == QtCore.Qt.Key_Alt: