bacup.py

def MyClass()
  def __init__(self, data):
    self._backups = deque()
    self.data = data
  
  def copy(self):
    return MyClass(self.data)
    
  def backup(self):
        """Creates a copy of self and keeps a reference to it
        in the self.backups stack.

        """
        print('backing up')
        self._backups.append(self.copy())

    def restore(self):
        print('Restoring')
        # This doesn't seem to work
        self = self._backups.pop()

here is the function decorator that comes with it:

def do_undo(func):
    """Decorator that creates a copy of the first argument
    (usually an epithelium object) and restores it if the function fails.

    The first argument in `*args` should have a `backup()` method.
    """
    def with_bckup(*args, **kwargs):
        eptm = args[0]
        eptm.backup()
        try:
            print('Trying ...')
            return func(*args, **kwargs)
        except Exception as err:
            print('Something bad happened, reverting')
            eptm.restore()
            raise err
    return with_bckup