Python版

 

https://github.com/faif/python-patterns/blob/master/behavioral/memento.py

#!/usr/bin/env python# -*- coding: utf-8 -*-"""http://code.activestate.com/recipes/413838-memento-closure/*TL;DR80Provides the ability to restore an object to its previous state."""from copy import copyfrom copy import deepcopydef memento(obj, deep=False):    state = deepcopy(obj.__dict__) if deep else copy(obj.__dict__)    def restore():        obj.__dict__.clear()        obj.__dict__.update(state)    return restoreclass Transaction(object):    """A transaction guard.    This is, in fact, just syntactic sugar around a memento closure.    """    deep = False    states = []    def __init__(self, deep, *targets):        self.deep = deep        self.targets = targets        self.commit()    def commit(self):        self.states = [memento(target, self.deep) for target in self.targets]    def rollback(self):        for a_state in self.states:            a_state()class Transactional(object):    """Adds transactional semantics to methods. Methods decorated  with    @Transactional will rollback to entry-state upon exceptions.    """    def __init__(self, method):        self.method = method    def __get__(self, obj, T):        def transaction(*args, **kwargs):            state = memento(obj)            try:                return self.method(obj, *args, **kwargs)            except Exception as e:                state()                raise e        return transactionclass NumObj(object):    def __init__(self, value):        self.value = value    def __repr__(self):        return '<%s: %r>' % (self.__class__.__name__, self.value)    def increment(self):        self.value += 1    @Transactional    def do_stuff(self):        self.value = '1111'  # <- invalid value        self.increment()  # <- will fail and rollbackif __name__ == '__main__':    num_obj = NumObj(-1)    print(num_obj)    a_transaction = Transaction(True, num_obj)    try:        for i in range(3):            num_obj.increment()            print(num_obj)        a_transaction.commit()        print('-- committed')        for i in range(3):            num_obj.increment()            print(num_obj)        num_obj.value += 'x'  # will fail        print(num_obj)    except Exception as e:        a_transaction.rollback()        print('-- rolled back')    print(num_obj)    print('-- now doing stuff ...')    try:        num_obj.do_stuff()    except Exception as e:        print('-> doing stuff failed!')        import sys        import traceback        traceback.print_exc(file=sys.stdout)    print(num_obj)### OUTPUT #### 
      
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          # -- committed# 
          
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             # -- rolled back# 
             
              # -- now doing stuff ...# -> doing stuff failed!# Traceback (most recent call last):# File "memento.py", line 97, in 
              
               # num_obj.do_stuff()# File "memento.py", line 52, in transaction# raise e# File "memento.py", line 49, in transaction# return self.method(obj, *args, **kwargs)# File "memento.py", line 70, in do_stuff# self.increment() # <- will fail and rollback# File "memento.py", line 65, in increment# self.value += 1# TypeError: Can't convert 'int' object to str implicitly#