PyQt center and top on window 화면중간 생성,팝업 유지

class MyForm(QtGui.QMainWindow):
   
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        QtGui.QMainWindow.__init__(self, None, QtCore.Qt.WindowStaysOnTopHint)#stay top 팝업 최상단 유지
        self.ui = Ui_Form()
        self.ui.setupUi(self)
        QtCore.QObject.connect(self.ui.pushButton,QtCore.SIGNAL("clicked()"),self.makeMat)
        self.centerScreen()#쌘터함수 실행
    def centerScreen(self):#화면중반부에 출력
        resolution = QtGui.QDesktopWidget().screenGeometry()
        self.move((resolution.width() / 2) - (self.frameSize().width() / 2),
                  (resolution.height() / 2) - (self.frameSize().height() / 2))
    def makeMat(self):
        sizex_ = 100
        sizey_ = 100
        geo = hou.node("/obj").createNode("geo","Ocean")
        geo.children()[0].destroy()
        grid_ = geo.createNode("grid")
        grid_.setParms({"sizex":sizex_,"sizey":sizey_})