Creating an object that can track when its attributes are modified

Steven D'Aprano steve+comp.lang.python at
Thu Mar 7 01:07:02 CET 2013

On Wed, 06 Mar 2013 08:56:09 -0800, Ben Sizer wrote:

> I need to be able to perform complex operations on the object that may
> modify several properties, and then gather the properties at the end as
> an efficient way to see what has changed and to store those changes. Any
> comparison of before-and-after snapshots could work in theory, but in
> practice it could be expensive to produce the snapshots on larger
> objects and probably expensive to calculate the differences that way
> too. Performance is important so I would probably just go for an
> explicit function call to mark an attribute as having been modified
> rather than trying to do a diff like that. (It wouldn't work for
> rollbacks, but I can accept that.)

Premature optimization.

Unless you have been eating and breathing Python code for 15+ years, your 
intuition of what is expensive and what isn't will probably be *way* off. 
I've been using Python for ~15 years, and I wouldn't want to try to guess 
what the most efficient way to do this will be.

Actually I lie. I would guess that the simple, most obvious way is 
faster: don't worry about storing what changed, just store *everything*. 
But I could be wrong.

Fortunately, Python development is rapid enough that you can afford to 
develop this object the straightforward way, profile your application to 
see where the bottlenecks are, and if it turns out that the simple 
approach is too expensive, then try something more complicated.


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