问如何通过子类化QNetworkAccessManager来使用createRequest伪造请求？

EN

import sys,urllib,time,os
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from PyQt4.QtWebKit import *
from PyQt4.QtNetwork import *
from PIL import Image

class NetworkAccessManager(QNetworkAccessManager):
    def __init__(self,old_manager):
    QNetworkAccessManager.__init__(self)
    self.old_manager = old_manager
    self.setCache(old_manager.cache())
    self.setCookieJar(old_manager.cookieJar())
    self.setProxy(old_manager.proxy())
    self.setProxyFactory(old_manager.proxyFactory())
    self.imreply=None
    self.reqstr=None
    self.otherreply=None
    self.current_req=None
    self.cnt=0
    self.jpgName="test.jpg"
    self.first=True
    self.ba=QByteArray()
    self.ba.clear()

    def createRequest(self, operation, request, data):
        req = request.url().toString()
        if req.contains(QString("zoom=")) and req.contains(QString("ss2jpg")) and not req.contains(QString("pi=2")):
            strreq=str(req)
            l=strreq.find("jid=")
            r=strreq.find(".jpg&a")
            self.jpgName=strreq[l+5:r+4]
            self.jpgcnt=int(strreq[l+5:r])
            print self.jpgName,self.jpgcnt
            self.imreply=QNetworkAccessManager.createRequest(self,operation, request, data)
            self.connect(self.imreply,SIGNAL("readyRead()"),self.saveImage)
            return self.imreply
        elif req.contains(QString("uf=ssr")):
            strreq=str(req)
            self.reqstr=strreq
            self.current_req=request
            r=strreq.find("?")
            self.jpgcnt=int(strreq[r-6:r])
            self.otherreply=QNetworkAccessManager.createRequest(self,operation, request, data)
            return self.otherreply
        else:
            return QNetworkAccessManager.createRequest(self,operation, request, data)

    def saveImage(self):
        if self.imreply.header(QNetworkRequest.ContentTypeHeader).toString().contains(QString("image/jpeg")) or self.imreply.header(QNetworkRequest.ContentTypeHeader).toString().contains(QString("image/png")):
            contentLen,flag = QString(self.imreply.rawHeader("Content-Length")).toInt()
            self.ba=self.ba.append(self.imreply.readAll())
            if self.ba.size() == contentLen:
            #self.ba=self.imreply.readAll()
            im=QImage.fromData(self.ba)
            im.save(self.jpgName)
            im=Image.open(self.jpgName)
            print "saving image",contentLen,self.jpgName
            im.save(self.jpgName)
            self.ba.clear()
            self.emit(SIGNAL("nextPage()"))

class dxWebView(QWebView):
    def __init__(self):
        QWebView.__init__(self)

    def clickNext(self):
        manager=self.page().networkAccessManager()
        if manager.cnt<50:
            nextreq=manager.current_req
            nexturl=manager.reqstr.replace(str(manager.jpgcnt),str(manager.jpgcnt+1))
            print "next url",nexturl
            nextreq.setUrl(QUrl(nexturl))
            manager.get(QNetworkRequest(nextreq))
            manager.cnt=manager.cnt+1

def main():
    app=QApplication(sys.argv)
    QWebSettings.globalSettings().setAttribute(QWebSettings.PluginsEnabled, True);
    view=dxWebView()
    old_manager=view.page().networkAccessManager()
    new_manager=NetworkAccessManager(old_manager)
    view.page().setNetworkAccessManager(new_manager)
    QObject.connect(new_manager,SIGNAL("nextPage()"),view.clickNext)
    url="http://www.yishuleia.cn/DrsPath.do?kid=686A67696A6F6A673134343438303337&username=gdnz2&spagenum=201&pages=50&fid=14813857&a=3fc3e380601ced0f08749c964294120e&btime=2013-04-03&etime=2013-04-23&template=bookdsr1&firstdrs=http%3A%2F%2Fbook.duxiu.com%2FbookDetail.jsp%3FdxNumber%3D000008299393%26d%3D592DC22226A893A958A6578E7D039A43"
    view.load(QUrl(url))
    view.show()
    sys.exit(app.exec_())

if __name__=='__main__':
    main()