PySide QSingleApplication

singleapp.py

class QSingleApplication(QApplication):
    def single_start(self, widget):
        self.widget = widget
        self.local_socket = QLocalSocket()
        self.local_socket.connected.connect(self.another_instance_started)
        self.local_socket.error.connect(self.first_instance)
        self.local_socket.connectToServer("foobar", QIODevice.WriteOnly)

    def another_instance_started(self):
        self.local_socket.write("foobar")
        self.local_socket.bytesWritten.connect(self.quit)

    def first_instance(self):
        self.local_server = QLocalServer()
        if self.local_server.listen("foobar"):
            self.local_server.newConnection.connect(self.tried_to_start_another_instance)
            self.widget.show()

    def tried_to_start_another_instance(self):
        def read():
            f = self.new_socket.readLine()
            self.widget.getArgsFromOtherInstance(str(f))
            self.widget.activateWindow()
            self.widget.show()
        self.new_socket = self.local_server.nextPendingConnection()
        self.new_socket.readyRead.connect(read)