title: Make QPushButton close all open program windows
body: <p>I'm trying to follow <a href="http://zetcode.com/tutorials/pyqt4/firstprograms/" rel="nofollow">this</a> tutorial, however it's made for PyQt4 whilst I'm using PyQt5.</p>
  
  <p>I have a <code>QPushButton</code> object called <code>btn</code> and want its <code>clicked()</code> signal to trigger the <code>QApplication</code> <code>closeAllWindows()</code> slot. I've read the documentation but it doesn't seem to help, I'm new to Python. </p>
  
  <p>Does anybody know how to do this?</p>