# -*- coding: utf-8 -*-
from PySide2 import  QtWidgets,QtOpenGL
class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        QtWidgets.qApp.lastWindowClosed.connect(self.lastWindowClosed)
        self.openGlWidget = QtOpenGL.QGLWidget(self)  # +1 
        self.dock = QtWidgets.QDockWidget(self)       # +1 si y'a un QGLWidget quelque part ! 
        self.dock.setWidget(self.openGlWidget)        # +2
        self.i = 0
      
    def lastWindowClosed(self):
        self.i +=1
        print(self.i)
        #QtWidgets.qApp.lastWindowClosed.disconnect(self.lastWindowClosed)
        
if __name__ == "__main__":  
    import sys
    app = QtWidgets.QApplication(sys.argv)    
    widget = MainWindow()
    widget.show()
    app.exec_()