python-patterns/memento.py at master · github4ry/python-patterns · GitHub

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#!/usr/bin/env python

# -*- coding: utf-8 -*-

"""http://code.activestate.com/recipes/413838-memento-closure/"""

from copy import copy, deepcopy

def memento(obj, deep=False):

state = copy(obj.__dict__) if deep else deepcopy(obj.__dict__)

def restore():

obj.__dict__.clear()

obj.__dict__.update(state)

return restore

class Transaction:

"""A transaction guard.

This is, in fact, just syntactic sugar around a memento closure.

"""

deep = False

states = []

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 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 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 do_stuff(self):

self.value = '1111' # <- invalid value

self.increment() # <- will fail and rollback

if __name__ == '__main__':

num_obj = NumObj(-1)

print(num_obj)

a_transaction = Transaction(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 ###

# <NumObj: -1>

# <NumObj: 0>

# <NumObj: 1>

# <NumObj: 2>

# -- committed

# <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 97, in <module>

# 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

# <NumObj: 2>

python-patterns/memento.py at master · github4ry/python-patterns · GitHub

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