Memento
Software to create checkpoints and rollback for your data
What is Memento
Memento is a software capable of create a checkpoint (many of them) and rollback to them. This checkpoints are associated to a specific data. You can only use Memento on python objects.
What is not Memento
Memento cant generate a checkpoint for an entire context. For now at least.
How to use
As context manager
You can create a memento instance as a context manager.
from memento import Memento
class A:
def __init__(self, a):
self.v = a
def inc(self, v=1):
self.v += v
a = A(4)
a.inc()
with Memento(a) as m:
a.inc()
print(a.v) # 6
m()
print(a.v) # 5As a context manager with automatic rollback
a = A(4)
a.inc()
print(a.v) # 5
with Memento(a, rollback_on_exc=True) as m:
a.inc()
print(a.v) # 6
a.inc("2") # --> Raises an exception
print(a.v) # 5As a context manager with error handling
def handler(exc, obj):
print(exc) # ValueError
print(obj.v) # 6
a = A(4)
a.inc()
print(a.v) # 5
with Memento(a, exc_cb=handler, rollback_on_exc=True) as m:
a.inc()
print(a.v) # 6
a.inc("2") # --> Raises an exception
print(a.v) # 5As a normal instance
a = A(4)
a.inc()
print(a.v) # 5
m = Memento(a)
a.inc()
print(a.v) # 6
m()
print(a.v) # 5How to change how Memento keep the state
You have to define two functions. One for copy the data, and another to recover the state.
class A:
def __init__(self, v):
self.v = v
def inc(self, v=1):
self.v += 1
def copy(self):
return self.v
def restore(self, data):
self.v = data
a = A(4)
m = Memento(a, copy_method=lambda x: x.copy(), recovery_method=lambda x, data: x.restore(data))
a.inc()
print(a.v) # 5
m()
print(a.v) # 4
