gistfile1.txt

# Copied and modified from http://stackoverflow.com/a/12712362/605356

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

import logging, sys
LOGVARSTR = "%25s = '%s'"

class QtSingleApplication(QApplication):

    messageReceived = pyqtSignal(unicode)

    def __init__(self, id, *argv):

        logfunc = logging.info
        logfunc(sys._getframe().f_code.co_name + '()')
    
        super(QtSingleApplication, self).__init__(*argv)
        self._id = id
        self._activationWindow = None
        self._activateOnMessage = False

        # Is there another instance running?
        self._outSocket = QLocalSocket()
        self._outSocket.connectToServer(self._id)
        self._isRunning = self._outSocket.waitForConnected()

        self._outStream = None
        self._inSocket  = None
        self._inStream  = None
        self._server    = None

        if self._isRunning:
            # Yes, there is.
            self._outStream = QTextStream(self._outSocket)
            self._outStream.setCodec('UTF-8')
        else:
            # No, there isn't, at least not properly.
            # Cleanup any past, crashed server.
            error = self._outSocket.error()
            logfunc(LOGVARSTR % ('self._outSocket.error()', error))
            if error == QLocalSocket.ConnectionRefusedError:
                logfunc('received QLocalSocket.ConnectionRefusedError; ' + \
                        'removing server.')
                self.close()
                QLocalServer.removeServer(self._id)
            self._outSocket = None
            self._server = QLocalServer()
            self._server.listen(self._id)
            self._server.newConnection.connect(self._onNewConnection)

        logfunc(sys._getframe().f_code.co_name + '(): returning')

    def close(self):
        logfunc = logging.info
        logfunc(sys._getframe().f_code.co_name + '()')
        if self._inSocket:
            self._inSocket.disconnectFromServer()
        if self._outSocket:
            self._outSocket.disconnectFromServer()
        if self._server:
            self._server.close()
        logfunc(sys._getframe().f_code.co_name + '(): returning')

    def isRunning(self):
        return self._isRunning

    def id(self):
        return self._id

    def activationWindow(self):
        return self._activationWindow

    def setActivationWindow(self, activationWindow, activateOnMessage = True):
        self._activationWindow = activationWindow
        self._activateOnMessage = activateOnMessage

    def activateWindow(self):
        if not self._activationWindow:
            return
        self._activationWindow.setWindowState(
            self._activationWindow.windowState() & ~Qt.WindowMinimized)
        self._activationWindow.raise_()
        self._activationWindow.activateWindow()

    def sendMessage(self, msg):
        if not self._outStream:
            return False
        self._outStream << msg << '\n'
        self._outStream.flush()
        return self._outSocket.waitForBytesWritten()

    def _onNewConnection(self):
        if self._inSocket:
            self._inSocket.readyRead.disconnect(self._onReadyRead)
        self._inSocket = self._server.nextPendingConnection()
        if not self._inSocket:
            return
        self._inStream = QTextStream(self._inSocket)
        self._inStream.setCodec('UTF-8')
        self._inSocket.readyRead.connect(self._onReadyRead)
        if self._activateOnMessage:
            self.activateWindow()

    def _onReadyRead(self):
        while True:
            msg = self._inStream.readLine()
            if not msg: break
            self.messageReceived.emit(msg)