PyQt Base in Maya window

from PyQt4 import QtGui, QtCore #QtCore added
import maya.cmds as cmds #######Added
import sip

windowTitle = "Scene Manip"#######Added
windowObject = "pySceneManipWin"#######Added

def getMainWindow():#######Added
    import maya.OpenMayaUI as mui#######Added
    pointer = mui.MQtUtil.mainWindow()#######Added
    return sip.wrapinstance(long(pointer), QtCore.QObject)#######Added


class SceneManipWin(QtGui.QMainWindow): #QWidget changed to QMainWindow
    def __init__(self, parent=None):# parent=None added
        super(SceneManipWin, self).__init__(parent) #parent added

        self.setObjectName(windowObject)#######Added
        self.setWindowTitle(windowTitle)#######Added

        self.mainWidget = QtGui.QWidget()#######Added
        self.setCentralWidget(self.mainWidget)#######Added

        #Building a layout
        self.gridLayout = QtGui.QGridLayout()
        self.mainWidget.setLayout(self.gridLayout)#self.setLayout(self.gridLayout) TO self.mainWidget.setLayout(self.gridLayout)

        #Objects for our window
        self.label = QtGui.QLabel("Work Area")
        self.fillList_pb = QtGui.QPushButton("Fill List")
        self.sceneSelect_pb = QtGui.QPushButton("Select in Scene")

        self.gridLayout.addWidget(self.label)
        self.gridLayout.addWidget(self.fillList_pb)
        self.gridLayout.addWidget(self.sceneSelect_pb)

def mayaRun():
    if cmds.window(windowObject, q=True, exists=True):  #####Added
        cmds.deleteUI(windowObject)  #########Added
    global gui
    gui = SceneManipWin(getMainWindow()) #### getMainWindow Added
    gui.show()

mayaRun()