title: RuntimeError: Please destroy the QApplication singleton before creating a new QApplication instance
body: <p>When i run python-pyside2 project server first, then it works well.<br>
  And the site also work well, but if i press F5 btn to refresh in browser.<br>
  Site shows error page Runtime at/</p>
  
  <p><img src="https://i.stack.imgur.com/vitkw.png" alt=""></p>
  
  <pre><code>import sys
  
  from urllib.request import urlopen  
  from bs4 import BeautifulSoup 
  
  from PySide2.QtGui import *  
  from PySide2.QtCore import *  
  from PySide2.QtWebKitWidgets import *  
  from PySide2.QtWidgets import QApplication 
  
  class dynamic_render(QWebPage):
  
      def __init__(self, url):
          self.frame = None
          self.app = QApplication(sys.argv)
          QWebPage.__init__(self)
          self.loadFinished.connect(self._loadFinished)  
          self.mainFrame().load(QUrl(url))
          QTimer.singleShot(0, self.sendKbdEvent)
          QTimer.singleShot(100, app.quit)
          self.app.exec_()
  
      def _loadFinished(self, result):  
          self.frame = self.mainFrame()  
          self.app.quit()
          self.app = None
  </code></pre>
  
  <p>Below, scaping code using pyside2:</p>
  
  <p>I don't know how can i fix it?<br>
  Best regards.<br>
  Thanks.  </p>