PyQt with Tornado

pyqtornado.py

"""Demonstration of combining the Qt and Tornado event loops."""

from PyQt4 import QtGui, QtCore
from tornado.ioloop import IOLoop
from tornado import gen
from tornado.httpclient import AsyncHTTPClient

URL = "https://www.random.org/integers/?num=1&min=100&max=999&col=1&base=10&format=plain&rnd=new"

class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)
        self.label = QtGui.QLabel("Label!")
        self.setCentralWidget(self.label)

    def closeEvent(self, event):
        IOLoop.instance().stop()

    @gen.coroutine
    def update_label(self):
        label = yield AsyncHTTPClient().fetch(URL)
        if label.error:
            self.label.setText("Error!")
        else:
            self.label.setText(label.body.decode('utf-8'))

if __name__ == "__main__":
    import sys
    from threading import Thread
    
    Thread(target=lambda: IOLoop.instance().start()).start()

    app = QtGui.QApplication(sys.argv)
    win = MainWindow()
    win.show()
    timer = QtCore.QTimer()
    timer.setInterval(1000)
    timer.timeout.connect(win.update_label)
    timer.start()
    sys.exit(app.exec_())

Nice fix, however it doesn't always work since the part after the yield statement is not executed in the main thread, see my solution here:
https://gist.github.com/maartenbreddels/9a31e4025ef9cc0ee68a