Creating an object that can track when its attributes are modified
Schneider
js at globe.de
Thu Mar 7 07:21:00 EST 2013
Hi,
maybe you could do this by a decorator on the setattr method. It should
look more or less
like your implementation, but in my eyes it's a cleaner and can be reused.
Further, I would use a stack for each attribute, so that you can restore
all previous values.
bg,
Johannes
On 03/06/2013 05:07 PM, Ben Sizer wrote:
> I am trying to make an object that can track when its attributes have been assigned new values, and which can rollback to previous values where necessary. I have the following code which I believe works, but would like to know if there are simpler ways to achieve this goal, or if there are any bugs I haven't seen yet.
>
>
> class ChangeTrackingObject(object):
> def __init__(self):
> self.clean()
>
> def clean(self):
> """Mark all attributes as unmodified."""
> object.__setattr__(self, '_dirty_attributes', dict())
>
> def dirty_vals(self):
> """Returns all dirty values."""
> return dict( [ (k,v) for k,v in self.__dict__.iteritems() if k in self._dirty_attributes] )
>
> def get_changes_and_clean(self):
> """Helper that collects all the changes and returns them, cleaning the dirty flags at the same time."""
> changes = self.dirty_vals()
> self.clean()
> return changes
>
> def rollback(self):
> """Reset attributes to their previous values."""
> for k,v in self._dirty_attributes.iteritems():
> object.__setattr__(self, k, v)
> self.clean()
>
> def __setattr__(self, key, value):
> # If the first modification to this attribute, store the old value
> if key not in self._dirty_attributes:
> if key in self.__dict__:
> self._dirty_attributes[key] = object.__getattribute__(self, key)
> else:
> self._dirty_attributes[key] = None
> # Set the new value
> object.__setattr__(self, key, value)
>
>
> I am aware that adding a new attribute and then calling rollback() leaves the new attribute in place with a None value - maybe I can use a special DeleteMe marker object in the _dirty_attributes dict along with a loop that calls delattr on any attribute that has that value after a rollback.
>
> I also believe that this won't catch modification to existing attributes as opposed to assignments: eg. if one of the attributes is a list and I append to it, this system won't notice. Is that something I can rectify easily?
>
> Any other comments or suggestions?
>
> Thanks,
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