[PyQt] Detecting second copy of program in memory.[SOLVED]

[Igor Prischepoff]

Hello, I have found solution for my problem.
So this post only for archiving in email list.
  Attaching example is a python version of this solution:
http://wiki.qtcentre.org/index.php?title=SingleApplication

  It is possible to detect second instance of application and to send 
some string to it (sys.argv in my case).
Thanks to all who answered my questions in this list!
---
igor at tyumbit.ru
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import sys
import thread,socket

from PyQt4.QtCore import *
from PyQt4.QtGui import * 
from PyQt4.QtNetwork import *

timeout=1000

class SingleApplication(QApplication):
    def __init__(self,   argv, uniqueKey):
        super(SingleApplication, self).__init__(argv)
        self._uniqueKey = uniqueKey
        self.sharedMemory = QSharedMemory(self._uniqueKey)
        if self.sharedMemory.attach():
            self._isRunning = True
        else:
            self._isRunning = False
            if not self.sharedMemory.create(1):
                print "Unable to create single instance"
                return
            self.localServer = QLocalServer(self)
            self.connect(self.localServer, SIGNAL("newConnection()"), self.receiveMessage)
            self.localServer.listen(self._uniqueKey)
    def receiveMessage(self):
        localSocket = self.localServer.nextPendingConnection()
        if not localSocket.waitForReadyRead(timeout):
            print localSocket.errorString().toLatin1()
            return
        byteArray = localSocket.readAll()
        self.emit(SIGNAL("messageAvailable"), byteArray)
        localSocket.disconnectFromServer()
    def isRunning(self):
        return self._isRunning
    def sendMessage(self, message):
        if not self._isRunning:
            return False
        localSocket = QLocalSocket(self)
        localSocket.connectToServer(self._uniqueKey, QIODevice.WriteOnly)
        if not localSocket.waitForConnected(timeout):
            print localSocket.errorString().toLatin1()
            return False
        localSocket.write(message)
        if not localSocket.waitForBytesWritten(timeout):
            print localSocket.errorString().toLatin1()
            return False
        localSocket.disconnectFromServer()
        return True

def dumpMessage(data):
    print data
if __name__ == '__main__':
    app = SingleApplication( sys.argv,"key" )
    if app.isRunning():
        print "second copy detected!"
        app.sendMessage("message from other instance:"+str(sys.argv))
        sys.exit(0)

    form = QMainWindow(None)
    QObject.connect(app, SIGNAL("messageAvailable"), dumpMessage)
    form.show()
    sys.exit(app.exec_())