GUI Problem: main.py

#!/usr/bin/python

import sys
import os
import time
import multiprocessing

from PyQt4 import QtCore
from PyQt4 import QtGui
from test import Ui_MainWindow

import script

class StreamWrapper:
    def __init__(self, stream, thread, mutex):
        self.stream = stream
        self.thread = thread
        self.mutex  = mutex

    def write(self, msg):
        with QtCore.QMutexLocker(self.mutex):
            self.thread.emit(QtCore.SIGNAL('update_console(QString)'), msg)
            self.stream.write(msg)

class RunInThread(QtCore.QThread):
    def __init__(self):
        QtCore.QThread.__init__(self)
        self.mutex = QtCore.QMutex()
        self.running = False

    def __del__(self):
        self.wait()

    def clean_exit(self, exit_code):
        self.exit(exit_code)

    def run(self):
        sys.stdout = StreamWrapper(sys.stdout, self, self.mutex)
        sys.stderr = StreamWrapper(sys.stderr, self, self.mutex)
        sys.exit = self.clean_exit

        try:
            self.script = script.Script()

            self.script.run()

            self.running = True
        except SystemExit as e:
            print 'Script terminated'


        self.emit(QtCore.SIGNAL('unlock_button'))
        self.running = False

        return


class Driver(QtGui.QMainWindow):
    def __init__(self):
        super(Driver, self).__init__()
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)

        self.ui.pushButton.clicked.connect(self.run_script)

        self.show()


    def run_script(self):
        self.ui.pushButton.setEnabled(False)
        self.thread = RunInThread()
        self.connect(self.thread, QtCore.SIGNAL('update_console(QString)'), self.ui.plainTextEdit.insertPlainText)
        self.connect(self.thread, QtCore.SIGNAL('unlock_button'), lambda: self.ui.pushButton.setEnabled(True))
        self.thread.start()

    def closeEvent(self, event):
        if hasattr(self, 'thread') and self.thread.running and hasattr(self.thread, 'script'):
            self.thread.script.suspend()
            self.thread.wait()
        super(Driver, self).closeEvent(event)

def main():
    app = QtGui.QApplication(sys.argv)
    ex  = Driver()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()