title: PyQt4 center window on active screen
body: <p>How I can center window on active screen but not on general screen? This code moves window to center on general screen, not active screen:</p>
  
  <pre><code>import sys
  from PyQt4 import QtGui
  
  class MainWindow(QtGui.QWidget):
  
      def __init__(self):
          super(MainWindow, self).__init__()
  
          self.initUI()
  
      def initUI(self):
  
          self.resize(640, 480)
          self.setWindowTitle('Backlight management')
          self.center()
  
          self.show()
  
      def center(self):
          frameGm = self.frameGeometry()
          centerPoint = QtGui.QDesktopWidget().availableGeometry().center()
          frameGm.moveCenter(centerPoint)
          self.move(frameGm.topLeft())
  
  def main():
      app = QtGui.QApplication(sys.argv)
      mainWindow = MainWindow()
      sys.exit(app.exec_())
  
  if __name__ == '__main__':
      main()
  </code></pre>
  
  <p>If I removes <b>self.center()</b> from <b>initUI()</b> then window opened on 0x0 on active screen. I need to open window on active screen and move this window on center of this screen. Thansk!</p>