= Writing a client for a zeromq service =

On the `#pyqt` channel on [[http://freenode.net|Freenode]], `Nils^` asked for a way to write a GUI client for a [[http://www.zeromq.org|zeromq]] service, using the [[http://www.zeromq.org/bindings:python|Python bindings]].

We decided to try using a worker thread to monitor the socket that connects the client to the server, emitting a signal whenever new data is received.

{{{
#!python

##############################################################################
##                                                                          ## 
##  adapted from http://zguide.zeromq.org/py:wuserver                       ##
##                                                                          ## 
##############################################################################


import sys
import zmq

from PyQt4 import QtCore, QtGui        
                
class ZeroMQ_Listener(QtCore.QObject):

    message = QtCore.pyqtSignal(str)
    
    def __init__(self):
       
        QtCore.QObject.__init__(self)
        
        # Socket to talk to server
        context = zmq.Context()
        self.socket = context.socket(zmq.SUB)

        print "Collecting updates from weather server"
        self.socket.connect ("tcp://localhost:5556")

        # Subscribe to zipcode, default is NYC, 10001
        filter = str(app.arguments()[1]) if len(app.arguments()) > 1 else "10001"
        self.socket.setsockopt(zmq.SUBSCRIBE, filter)
        
        self.running = True
    
    def loop(self):
        while self.running:
            string = self.socket.recv()
            self.message.emit(string)
            
class ZeroMQ_Window(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QMainWindow.__init__(self, parent)

        
        frame = QtGui.QFrame()
        label = QtGui.QLabel("listening")
        self.text_edit = QtGui.QTextEdit()
        
        layout = QtGui.QVBoxLayout(frame)
        layout.addWidget(label)
        layout.addWidget(self.text_edit)
        
        self.setCentralWidget(frame)

        self.thread = QtCore.QThread()
        self.zeromq_listener = ZeroMQ_Listener()
        self.zeromq_listener.moveToThread(self.thread)
        
        self.thread.started.connect(self.zeromq_listener.loop)
        self.zeromq_listener.message.connect(self.signal_received)
        
        QtCore.QTimer.singleShot(0, self.thread.start)
    
    def signal_received(self, message):
        self.text_edit.append("%s\n"% message)

    def closeEvent(self, event):
        self.zeromq_listener.running = False
        self.thread.quit()
        self.thread.wait()

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    
    mw = ZeroMQ_Window()
    mw.show()
    
    sys.exit(app.exec_())
}}}