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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""http://code.activestate.com/recipes/413838-memento-closure/"""
import copy
def Memento(obj, deep=False):
state = (copy.copy, copy.deepcopy)[bool(deep)](obj.__dict__)
def Restore():
obj.__dict__.clear()
obj.__dict__.update(state)
return Restore
class Transaction:
"""A transaction guard. This is really just
syntactic suggar arount a memento closure.
"""
deep = False
def __init__(self, *targets):
self.targets = targets
self.Commit()
def Commit(self):
self.states = [Memento(target, self.deep) for target in self.targets]
def Rollback(self):
for st in self.states:
st()
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:
state()
raise
return transaction
class 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 DoStuff(self):
self.value = '1111' # <- invalid value
self.Increment() # <- will fail and rollback
if __name__ == '__main__':
n = NumObj(-1)
print(n)
t = Transaction(n)
try:
for i in range(3):
n.Increment()
print(n)
t.Commit()
print('-- commited')
for i in range(3):
n.Increment()
print(n)
n.value += 'x' # will fail
print(n)
except:
t.Rollback()
print('-- rolled back')
print(n)
print('-- now doing stuff ...')
try:
n.DoStuff()
except:
print('-> doing stuff failed!')
import sys
import traceback
traceback.print_exc(file=sys.stdout)
pass
print(n)
### OUTPUT ###
# <NumObj: -1>
# <NumObj: 0>
# <NumObj: 1>
# <NumObj: 2>
# -- commited
# <NumObj: 3>
# <NumObj: 4>
# <NumObj: 5>
# -- rolled back
# <NumObj: 2>
# -- now doing stuff ...
# -> doing stuff failed!
# Traceback (most recent call last):
# File "memento.py", line 91, in <module>
# n.DoStuff()
# File "memento.py", line 47, in transaction
# return self.method(obj, *args, **kwargs)
# File "memento.py", line 67, in DoStuff
# self.Increment() # <- will fail and rollback
# File "memento.py", line 62, in Increment
# self.value += 1
# TypeError: Can't convert 'int' object to str implicitly
# <NumObj: 2>
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