Python 如何在oop风格的程序中强制PyQt按钮工作

当我打开pyqt窗口时，按钮看起来是对的，但按下时它什么也不做。我怎样才能解决这个问题

from PyQt4 import QtGui, QtCore
import os, sip, sys

from PyQt4.QtGui import *
from PyQt4.QtCore import *

from .ui.gui import Ui_MainWindow


class MainWindow(QtGui.QMainWindow, Ui_MainWindow):    
    def __init__(self, parent = None):
        super(MainWindow, self).__init__(parent,QtCore.Qt.Tool)
        self.initUI(self)


def show():    
    # Use a shared instance of QApplication
    import maya.OpenMayaUI as mui
    app = QtGui.QApplication.instance()
    # Get a pointer to the maya main window
    ptr = mui.MQtUtil.mainWindow()
    # Use sip to wrap the pointer into a QObject
    win = sip.wrapinstance(long(ptr), QObject)
    form = MainWindow(win)
    form.show()

---

---

在打印语句“doIt！”出现的地方是否有一个可见的终端？是的，当我在类外定义doIt函数时，它会被打印出来。

from PyQt4 import QtCore, QtGui
class Ui_MainWindow():

    def initUI(self, MainWindow):

        self.centralwidget = QtGui.QWidget(MainWindow)
        MainWindow.setCentralWidget(self.centralwidget)

        self.btnQuit = QtGui.QPushButton("x", self)       
        self.panel = QtGui.QHBoxLayout(self.centralwidget)   
        self.panel.addWidget(self.btnQuit)       
        self.btnQuit.clicked.connect(self.doIt)      

    def doIt(self, MainWindow):
        print "DO IT!"