code: def closeEvent(self, event):
      print("Closing main window!")
      self.closing.emit()
      return super().closeEvent(event)
  
imports: import time
  from math import sin, pi
  import numpy
  from PyQt5 import QtWidgets, QtCore
  from vispy.scene import SceneCanvas, visuals
  from vispy.app import use_app
label_desc: Use image node_id 3 for calling the MyMainWindow obj's underlying member method code with example usage: obj.closeEvent(event) and returns: super