title: Threading and Signals problem in PyQt
body: <p>I'm having some problems with communicating between Threads in PyQt. I'm using signals to communicate between two threads, a Sender and a Listener. The sender sends messages, which are expected to be received by the listener. However, no messages are receieved. Can anyone suggest what might be going wrong? I'm sure it must be something simple, but I've been looking around for hours and not found anything. Thanks in advance!</p>
  
  <pre><code>from PyQt4 import QtCore,QtGui
  import time
  
  class Listener(QtCore.QThread):    
      def __init__(self):
          super(Listener,self).__init__()
  
      def run(self):
          # just stay alive, waiting for messages
          print 'Listener started'
          while True:
              print '...'
              time.sleep(2)
  
      def say_hello(self):
          print ' --&gt; Receiver: Hello World!'
  
  class Sender(QtCore.QThread):
      # a signal with no arguments
      signal = QtCore.pyqtSignal()
  
      def __init__(self):
          super(Sender,self).__init__()
          # create and start a listener
          self.listener = Listener()
          self.listener.start()
          # connect up the signal
          self.signal.connect(self.listener.say_hello)
          # start this thread
          self.start()
  
      def run(self):
          print 'Sender starting'
          # send five signals
          for i in range(5):
              print 'Sender --&gt;'
              self.signal.emit()
              time.sleep(2)
          # the sender's work is done
          print 'Sender finished'
  </code></pre>