python如何通过pyqt5实现进度条

#!/usr/bin/python3
# -*- coding: utf-8 -*-

"""
PyQt5 教程

这个例子显示了一个进度条控件。
auther: 虚生
"""
import sys
from PyQt5.QtWidgets import QApplication, QWidget, QProgressBar, QPushButton
from PyQt5.QtCore import QBasicTimer

class Example(QWidget):

  def __init__(self):
    super().__init__()

    self.initUI()

  def initUI(self):

    self.pbar = QProgressBar(self)
    self.pbar.setGeometry(30, 40, 200, 25)

    self.btn = QPushButton('开始', self)
    self.btn.move(40, 80)
    self.btn.clicked.connect(self.doAction)

    self.timer = QBasicTimer()
    self.step = 0
    self.setGeometry(300, 300, 280, 170)
    self.setWindowTitle('进度条')
    self.show()

  def timerEvent(self, e):

    if self.step >= 100:
      self.step = 0
      self.pbar.setValue(self.step)
      self.timer.stop()
      self.btn.setText('完成')
      return
    self.step = self.step+1
    self.pbar.setValue(self.step)

  def doAction(self, value):
    print("do action")
    if self.timer.isActive():
      self.timer.stop()
      self.btn.setText('开始')
    else:
      self.timer.start(100, self)
      self.btn.setText('停止')

if __name__ == '__main__':
   app = QApplication(sys.argv)
   ex = Example()
   sys.exit(app.exec_())