Scrapy blocking spider that renders JavaScript with PyQt4

gistfile1.py

from PyQt4.QtCore import QUrl
from PyQt4.QtGui import QApplication
from PyQt4.QtWebKit import QWebPage

from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
from scrapy.spider import BaseSpider
from scrapy.http import HtmlResponse

class Render(QWebPage):
    def __init__(self, url):
        self.app = QApplication([url])
        QWebPage.__init__(self)
        self.loadFinished.connect(self._load_finished)
        self.mainFrame().load(QUrl(url))
        self.app.exec_()

    def _load_finished(self, result):
        self.app.quit()

    @property
    def html(self):
        return self.mainFrame().toHtml().toAscii().data()

class WebkitSpider(BaseSpider):
    name = 'webkit'
    allowed_domains = ['expedia.be']
    start_urls = ('http://www.expedia.be/Hotel-Search#regionId=601725',)

    def parse(self, response):
        url = response.request.url
        self.log('parse(): rendering %s' % url)

        xpath = ('id("searchResultsContainer")/div/'
                 'div[contains(@class,"hotels")]//a[@class="title"]')
        le = SgmlLinkExtractor(restrict_xpaths=xpath)
        r = HtmlResponse(url, body=Render(url).html)
        hotels = le.extract_links(r)
        self.log('parse(): found %d hotels' % len(hotels))