how to detect if a dictionary has been modified ?

[Paul Rubin]

Stef Mientki <stef.mientki at gmail.com> writes:
> Now I do it to make a copy of the dictionary and compare it with the
> old one.
> When a change is detected I nake a new copy and interpret the whole
> new dictionary again,
> so I'm not interested in knowing where the change(s) are located.
> This works well, but as I have many of these dictionaries,
> I find the copy a waste of time and space.

As a couple of people have said, you could make a dict subclass that
notices when you do updates.  I think the real answer is a
"functional" dictionary, which means one that is never updated.  You
instead make a new functional dictionary that shares structure with
the old one.  The functional dictionary uses a balanced-tree data
structure that makes this creation of new partially-shared
dictionaries efficient.  Look up "AVL tree" or "red-black tree" for
how they work.  

I've been wanting for a while to get around to coding some of these
structures in Python, but I'll be even happier if someone else beats
me to it.