[PyQt] trouble quitting application

[Soumen banerjee]

Hi,
Im new to PyQt4 and im having fun using it. but ive run into a bit of
a problem. I cant quit the application.
The application has 2 modules. The gui module(gui.py) and then the
main program(main.py)
heres gui.py:

from PyQt4 import QtCore, QtGui
import sys
from subprocess import Popen
class Ui_MainWindow(object):
	fileinit=False
	paused=True
	quit=False
	filename=""
	def setupUi(self, MainWindow):
		MainWindow.setObjectName("MainWindow")
		MainWindow.resize(394, 414)
		self.centralwidget = QtGui.QWidget(MainWindow)
		self.centralwidget.setObjectName("centralwidget")
		self.scrollArea = QtGui.QScrollArea(self.centralwidget)
		self.scrollArea.setGeometry(QtCore.QRect(19, 9, 361, 281))
		self.scrollArea.setWidgetResizable(True)
		self.scrollArea.setObjectName("scrollArea")
		self.scrollAreaWidgetContents = QtGui.QWidget(self.scrollArea)
		self.scrollAreaWidgetContents.setGeometry(QtCore.QRect(0, 0, 357, 277))
		self.scrollAreaWidgetContents.setObjectName("scrollAreaWidgetContents")
		self.textEdit = QtGui.QTextEdit(self.scrollAreaWidgetContents)
		self.textEdit.setGeometry(QtCore.QRect(-7, -6, 371, 291))
		self.textEdit.setObjectName("textEdit")
		self.scrollArea.setWidget(self.scrollAreaWidgetContents)
		self.pushButton = QtGui.QPushButton(self.centralwidget)
		self.pushButton.setGeometry(QtCore.QRect(30, 310, 80, 25))
		self.pushButton.setObjectName("pushButton")
		self.pushButton_2 = QtGui.QPushButton(self.centralwidget)
		self.pushButton_2.setGeometry(QtCore.QRect(139, 310, 91, 25))
		self.pushButton_2.setObjectName("pushButton_2")
		self.pushButton_3 = QtGui.QPushButton(self.centralwidget)
		self.pushButton_3.setGeometry(QtCore.QRect(280, 310, 80, 25))
		self.pushButton_3.setObjectName("pushButton_3")
		MainWindow.setCentralWidget(self.centralwidget)
		self.menubar = QtGui.QMenuBar(MainWindow)
		self.menubar.setGeometry(QtCore.QRect(0, 0, 394, 23))
		self.menubar.setObjectName("menubar")
		MainWindow.setMenuBar(self.menubar)
		self.statusbar = QtGui.QStatusBar(MainWindow)
		self.statusbar.setObjectName("statusbar")
		MainWindow.setStatusBar(self.statusbar)

		self.retranslateUi(MainWindow)
		QtCore.QObject.connect(self.pushButton, QtCore.SIGNAL("clicked()"), self.Open)
		QtCore.QObject.connect(self.pushButton_2,
QtCore.SIGNAL("clicked()"), self.Pause)
		QtCore.QObject.connect(self.pushButton_3,
QtCore.SIGNAL("clicked()"), self.Quit)
		QtCore.QMetaObject.connectSlotsByName(MainWindow)

	def retranslateUi(self, MainWindow):
		MainWindow.setWindowTitle(QtGui.QApplication.translate("MainWindow",
"MainWindow", None, QtGui.QApplication.UnicodeUTF8))
		self.pushButton.setText(QtGui.QApplication.translate("MainWindow",
"Open", None, QtGui.QApplication.UnicodeUTF8))
		self.pushButton_2.setText(QtGui.QApplication.translate("MainWindow",
"Pause/Resume", None, QtGui.QApplication.UnicodeUTF8))
		self.pushButton_3.setText(QtGui.QApplication.translate("MainWindow",
"Quit", None, QtGui.QApplication.UnicodeUTF8))
	def Pause(self):
		print "Pause"
		self.paused=not(self.paused)
	def Quit(self):
		self.quit=True
		print "setting quit"
	def Open(self):
		print "Open"
		self.filename=QtGui.QFileDialog.getOpenFileName()
		self.filename=str(self.filename)
		f=open("book.txt","r")
		old=f.read(20)
		f.close()
		f=open(self.filename,'r')
		new=f.read(20)
		f.close()
		if(old!=new):
			Popen('rm log.txt',shell=True)
			f=open("book.txt",'w')
			f.write(new)
			f.close()
		self.fileinit=True
		print "setting fileinit"
		

and heres the main.py

from PyQt4 import QtCore, QtGui
import sip,gui
import sys
from subprocess import Popen
from threading import Thread
class AppThread(Thread):
	appinit=False
	def run(self):
		app = QtGui.QApplication(sys.argv)
		MainWindow = QtGui.QMainWindow()
		self.ui = gui.Ui_MainWindow()
		self.ui.setupUi(MainWindow)
		MainWindow.show()
		self.appinit=True
		#ui.textEdit.setText(ui.filename)
		sys.exit(app.exec_())
class Speak(Thread):
	def run(self):
		print "starting speaker"
		try:
			log=open("log.txt",'r')
			print log
			self.index=log.read()
			log.close()
			self.index=int(self.index)
		except IOError:
			print "setting new"
			index=0
#by now, index has been defined for both a new and an old book
		self.book=open(a.ui.filename,'r')
		self.book.seek(self.index)
		while(a.ui.quit==False):
			if (a.ui.paused==False):
				sen=self.readsen()
				print sen
				#a.ui.textEdit.setText(sen)
				command="soundwrapper espeak "+' " '+sen+' " '
				k=Popen(command,shell=True)
				print "read sentence"
				k.wait()
		print "quitted loop"
		index=self.book.tell()
		log=open("log.txt","w")
		log.write(str(index))
		log.close()
		print "calling exit"
		sys.exit()
	def readsen(self):
		line=""
		sen=""
		while(line.find(".")== -1):
			sen=sen+line
			line=self.book.readline()
		sen=sen+line[0:line.find(".")+1]
		self.book.seek(self.book.tell()-len(line)+line.find(".")+1)
		return sen
a=AppThread()
a.start()
while 1:
	if a.appinit== True:
		if a.ui.fileinit==True:	
			s=Speak()
			s.start()
			break

so heres the problem:- when i hit the quit button, quit is set to high
(in the Gui module) and then the while loop in the speak thread
quits(printing quitting loop) and it updates the log file as its
supposed to do. then after it prints calling exit, the app freezes.
Isnt sys.exit() supposed to kill the interpreter? So, what is going
on? why does the app not quit?
Pls Help
Regards
Soumen