• if a user logins through LoginApp , on success opens MainMenu followed by the rest of the Windows (QWidget). In my case , this is what i have been using:

class MainMenu(QWidget):
      super().__init__()
      def __init__(self):
           # declare class attributes/variables that hold the application other windows
          self.mainTreeMenu = None
         # when a user performs an operation, e.g clicks a button set the instance of KsecOption or RoleMainWindow ..e.tc. to class variable
         self.mainTreeMenu = MainTreeMenu()
         self.mainTreeMenu.show()

To improve your application

• add a condition statement to always check if the application window is open and not None.
• setup a custom Signal emitter from your child window, which is then picked up by a slot(method) connected to that signal.