AttributeError: ‘module’ object has no attribute ‘QtString’

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Python

Hi My development eviroment:
os: windows xp
python: python-3.1.2.msi
pyqt: PyQt-Py3.1-gpl-4.7.4-1.exe

import sys
from PyQt4 import QtCore, QtGui
app = QtGui.QApplication(sys.argv)
s = QtCore.QtString()
sys.exit(app.exec_())

It always show me
in <module>
s = QtCore.QtString()
AttributeError: 'module' object has no attribute 'QtString'


I chaged code:

import sys
from PyQt4.QtGui import *
from PyQt4.QtCore import *
app = QApplication(sys.argv)
s = QtString()
sys.exit(app.exec_())

Then it always show me like this:
in <module>
s = QtString()
NameError: name 'QtString' is not defined

what should i do?