如何使用PyQT4进度条将当前值显示为“目标”值的百分比？

Question

我正在从xml文件导入一些数据（netSales），我希望将此数字与“目标值”进行比较，让我们将其指定为100。

我的代码如下（来自PyQT进度条教程加上我自己的一些代码）：

import sys
from PyQt4 import QtGui, QtCore
import xml.etree.ElementTree as ET

class Window(QtGui.QMainWindow):

    def __init__(self,goal=100000):
        super(Window, self).__init__()
        self.setGeometry(50, 50, 500, 300)
        self.setWindowTitle("Maar Dis Lekker!")
        self.setWindowIcon(QtGui.QIcon('sales.png'))

        extractAction = QtGui.QAction("&GET TO THE CHOPPAH!!!", self)
        extractAction.setShortcut("Ctrl+Q")
        extractAction.setStatusTip('Leave The App')
        extractAction.triggered.connect(self.close_application)

        self.statusBar()

        mainMenu = self.menuBar()
        fileMenu = mainMenu.addMenu('&File')
        fileMenu.addAction(extractAction)
        self.goal = goal

        self.home()

    def home(self):
        btn = QtGui.QPushButton("Quit", self)
        btn.clicked.connect(self.close_application)
        btn.resize(btn.minimumSizeHint())
        btn.move(0,100)

        label = QtGui.QLabel(self)
        pixmap = QtGui.QPixmap('BuildIt.png')
        label.setPixmap(pixmap)
        label.resize(label.minimumSizeHint())
        label.move(20,175)

        extractAction = QtGui.QAction(QtGui.QIcon('todachoppa.png'), 'Flee the Scene', self)
        extractAction.triggered.connect(self.close_application)

        self.toolBar = self.addToolBar("Extraction")
        self.toolBar.addAction(extractAction)

        checkBox = QtGui.QCheckBox('Shrink Window', self)
        checkBox.move(100, 25)
        checkBox.stateChanged.connect(self.enlarge_window)

        self.progress = QtGui.QProgressBar(self)
        self.progress.setGeometry(100, 80, 350, 80)


        self.show()


    def calculate(self):
        currentNetSales = self.getSalesData()

        while self.completed < self.goal:
            self.completed += 0.0001
            self.progress.setValue(self.completed)



    def enlarge_window(self, state):
        if state == QtCore.Qt.Checked:
            self.setGeometry(50,50, 1000, 600)
        else:
            self.setGeometry(50, 50, 500, 300)



    def close_application(self):
        choice = QtGui.QMessageBox.question(self, 'Extract!',
                                            "Get into the chopper?",
                                            QtGui.QMessageBox.Yes | QtGui.QMessageBox.No)
        if choice == QtGui.QMessageBox.Yes:
            print("Extracting Naaaaaaoooww!!!!")
            sys.exit()
        else:
            pass

    def getSalesData(self):
        tree = ET.parse('barSales.xml')
        root = tree.getroot()
        for row in root.findall(".//RECORD/ROW"):
            netSales = [float(row.attrib["nettsales"])]
        return netSales



def run():
    app = QtGui.QApplication(sys.argv)
    GUI = Window()
    sys.exit(app.exec_())


run()

问题：如何让条形图显示netSales相对于goalSales的百分比？