new_contents: #!/usr/bin/env python
  
  from structdata import g_project
  from openfilerooms import openRooms
  from savefilerooms import saveRooms
  from os import mkdir
  from os.path import exists
  from os import remove
  
  
  class UndoRedo(object):
  
  
      def __init__(self):
          self._list_of_project = []
          self._add_element = True
          self._list_index = 0
          g_project.subscribe(self)
  
      def undo(self):
          if self.moreUndo():
              self._list_index -= 1
              self._add_element = False
              openRooms(self._list_of_project[self._list_index - 1])
              g_project.notify("undoredo")
  
      def moreUndo(self):
          return self._list_index > -1
  
      def updateData(self):
          if self._add_element:
              self._list_index += 1
              self._list_of_project = self._list_of_project[:self._list_index]
              self._list_of_project.append(saveRooms())
          self._add_element = True
  
  g_undoredo = UndoRedo()
  
subject: add modulo to implent the UndoRedo class