QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.

#!/usr/bin/python
import sys
from PyQt4 import QtGui, QtCore, QtSql
from Ui_AddressBook import *


class AddressBook(QtGui.QMainWindow, Ui_MainWindow):
    def __init__(self, parent=None):
        QtGui.QMainWindow.__init__(self,parent)
        self.ui=Ui_MainWindow()
        self.ui.setupUi(self) 
        self.center()
       
    def center(self):
        screen = QtGui.QDesktopWidget().screenGeometry()
        size =  self.geometry()
        self.move((screen.width()-size.width())/2, (screen.height()-size.height())/2)
       
    def connections(self):
        self.connect(self.ui.btn_add, QtCore.SIGNAL('clicked()'), self.addEntry)
   
    def database(self):
        self.db = QtSql.QSqlDatabase.addDatabase("QSQLITE")
        self.db.setDatabaseName("book.db")
        self.db.open()
        self.query = QtSql.QSqlQuery()
        try:
            self.query.exec_('CREATE TABLE contacts (name TEXT,phone TEXT ,Email TEXT)')
        except:
            pass
        self.model = QtSql.QSqlTableModel(self)
        self.model.setTable("contacts")
        self.model.setEditStrategy(QtSql.QSqlTableModel.OnManualSubmit);
        self.model.select()
        self.model.setHeaderData(0, QtCore.Qt.Horizontal, ("Name"))
        self.model.setHeaderData(1, QtCore.Qt.Horizontal, ("Phone"))
        self.model.setHeaderData(2, QtCore.Qt.Horizontal, ("Email"))
        self.ui.tableView.setModel(self.model)
        self.ui.tableView.show()
       
    def addEntry(self):
        name=str(self.ui.txt_name.text())
        phone=str(self.ui.txt_phone.text())
        email=str(self.ui.txt_email.text())
        stmnt="INSERT INTO contacts (name,phone,email) ""VALUES ("+"'"+name+"',"+"'"+phone+"',"+"'"+email+"'"+")"
        self.query.exec_(stmnt)
       
def main():
    app = QtGui.QApplication(sys.argv)
    addressbook=AddressBook()
    addressbook.database()
    addressbook.show()
    addressbook.connections()
    sys.exit(app.exec_())
   

if __name__ == '__main__':
    main()

def  closeEvent(self, event):
        print 'clooooooooooooosing'
        self.db.close()
        QtSql.QSqlDatabase.removeDatabase('book.db')

#def main():
app = QtGui.QApplication(sys.argv)
addressbook=AddressBook()
addressbook.database()
addressbook.show()
addressbook.connections()

sys.exit(app.exec_())

#
#if __name__ == '__main__':
#    main()