"""
Transactions of attributes by inheriting the Transaction class
Basic Usage:
class Test(Transaction):
pass
a = Test()
a.test = "old state"
a.commit()
a.test = "bad state, roll me back"
a.rollback()
assert(a.test == "old state")
See also: http://www.harald-hoyer.de/linux/pythontransactionclass
Copyright (C) 2008 Harald Hoyer <harald@redhat.com>
Copyright (C) 2008 Red Hat, Inc.
"""
import copy
def _checksetseen(what, seen):
"checks and sets the obj id in seen"
if what in seen:
return True
seen.add(what)
return False
class Transaction(object):
"""
This class allows sub-classes to commit changes to an instance to a
history, and rollback to previous states.
Because the class only stores attributes in self.__dict__ sub-classes
need to use the methods __getstate__ and __setstate__ to provide additional
state information. See the Transactionlist below for an example usage.
"""
def commit(self, **kwargs):
"""
Commit the object state.
If the optional argument "deep" is set to False,
objects of class Transaction stored in this object will
not be committed.
"""
seen = kwargs.get("_commit_seen", set())
if _checksetseen(id(self), seen):
return
deep = kwargs.get("deep", True)
# Do not deepcopy the Transaction objects. We want to keep the
# reference. Instead commit() them.
state = dict()
for key, val in self.__dict__.items():
if isinstance(val, Transaction):
state[key] = val
if deep:
val.commit(_commit_seen = seen)
elif key == "__l":
# do not deepcopy our old state
state[key] = val
else:
state[key] = copy.deepcopy(val)
if hasattr(self, '__getstate__'):
state = (state, getattr(self, '__getstate__')())
self.__dict__["__l"] = state
def rollback(self, **kwargs):
"""
Rollback the last committed object state.
If the optional argument "deep" is set to False,
objects of class Transaction stored in this object will
not be rolled back.
"""
seen = kwargs.get("_rollback_seen", set())
if _checksetseen(id(self), seen):
return
deep = kwargs.get("deep", True)
state = None
extrastate = None
gotstate = False
gotextrastate = False
if "__l" in self.__dict__:
state = self.__dict__["__l"]
gotstate = True
if type(state) is tuple:
gotextrastate = True
(state, extrastate) = state
# rollback our childs, then ourselves
for child in self.__dict__.values():
if isinstance(child, Transaction):
if deep:
child.rollback(_rollback_seen = seen)
if gotstate:
self.__dict__.clear()
self.__dict__.update(state)
if gotextrastate and hasattr(self, '__setstate__'):
getattr(self, '__setstate__')(extrastate)
class Transactionlist(list, Transaction):
"""
An example subclass of list, which inherits transactions.
Due to the special list implementation, we need the
__getstate__ and __setstate__ methods.
See the code for the implementation.
"""
def commit(self, **kwargs):
"""
Commit the object state.
If the optional argument "deep" is set to False,
objects of class Transaction stored in this object will
not be committed.
"""
# make a local copy of the recursive marker
seen = set(kwargs.get("_commit_seen", set()))
super(Transactionlist, self).commit(**kwargs)
if _checksetseen(id(self), seen):
return
deep = kwargs.get("deep", True)
if deep:
for val in self:
if isinstance(val, Transaction):
val.commit()
def rollback(self, **kwargs):
"""
Rollback the last committed object state.
If the optional argument "deep" is set to False,
objects of class Transaction stored in this object will
not be rolled back.
"""
# make a local copy of the recursive marker
seen = set(kwargs.get("_rollback_seen", set()))
super(Transactionlist, self).rollback(**kwargs)
if _checksetseen(id(self), seen):
return
deep = kwargs.get("deep", True)
if deep:
for val in self:
if isinstance(val, Transaction):
val.rollback()
def __getstate__(self):
"""
return a deepcopy of all non Transaction class objects in our list,
and a reference for the committed Transaction objects.
"""
state = []
for val in self:
if isinstance(val, Transaction):
state.append(val)
else:
state.append(copy.deepcopy(val))
return state
def __setstate__(self, state):
"clear the list and restore all objects from the state"
del self[:]
self.extend(state)
__author__ = "Harald Hoyer <harald@redhat.com>"
