PyQT 的QtGui.qApp 不存在 ？ Linux运行正常

import sys
from PyQt4 import QtGui,QtCore
class Qbutton(QtGui.QWidget):
def init(self,parent=None):
QtGui.QWidget.__init__(self,parent)
self.setGeometry(1000,1000,200,400)
self.setWindowTitle("Rocky 3rd app")
quit=QtGui.QPushButton("RC",self)
quit.setGeometry(10,10,30,15)
self.connect(quit,QtCore.SIGNAL('clicked()'),QtGui,qApp,QtCore.SLOT('quit()'))
apps = QtGui.QApplication(sys.argv) 
qb=Qbutton()
qb.show()
sys.exit(apps.exec_())

为什么上面的PyQT代码在windows上说NameError: global name 'qApp' is not defined ？
而linux下却能够正常运行？？