code: def main_iteration(self):
          
          if self.show_vars:
              self.show_variables_window()
          else:
              self.hide_variables_window()
  
          for snapshot_f in self.scheduled_snapshots:
              fn = snapshot_f(self.last_draw_ctx)
              print("Saved snapshot: %s" % fn)
          else:
              self.scheduled_snapshots = deque()
  
          while Gtk.events_pending():
              Gtk.main_iteration()
docs: Called from main loop, if your sink needs to handle GUI events
          do it here.
  
          Check any GUI flags then call Gtk.main_iteration to update things.