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