gistfile1.py

class Action(object):
    def backward(self):
        raise NotImplemented

    def forward(self):
        raise NotImplemented


class Pipeline(object):
    def __init__(self, actions):
        self.actions = actions

    def execute(self):
        try:
            for action in self.actions:
                action.forward()
        except:
            self.rollback(action)

    def rollback(self, action):
        index = self.actions.index(action) - 1
        while index > 0:
            action = self.actions[index]
            action.backward()
            index = index - 1