self-aware list of objects able to sense constituent member alterations?

[Reckoner]

On Jan 28, 10:17 pm, Peter  Wang <misterw... at gmail.com> wrote:
> On Jan 27, 3:16 pm,Reckoner<recko... at gmail.com> wrote:
>
>
>
> > I'm not sure this is possible, but I would like to have
> > a list of  objects
>
> > A=[a,b,c,d,...,z]
>
> > where,  in the midst of a lot of processing I might do something like,
>
> > A[0].do_something_which_changes_the_properties()
>
> > which alter the properties of the object 'a'.
>
> > The trick is that I would like A to be mysteriously aware that
> > something about the  object 'a' has changed so that when I revisit A,
> > I will know that the other items in the list need to be refreshed to
> > reflect the changes in A as a result of changing 'a'.
>
> > Even better would be to automatically percolate the subsequent changes
> > that resulted from altering 'a' for the rest of the items in the list.
> > Naturally, all of these items are related in some parent-child
> > fashion.
>
> > that might be a lot to ask, however.
>
> > Any advice appreciated.
>
> You should really look at Enthought's Traits package.  It does exactly
> what you are asking for, and much, much more.  See:
>
> http://code.enthought.com/projects/traits/documentation.phphttp://code.enthought.com/projects/traits/examples.php
>
> Using Traits, you could do the following:
>
> from enthought.traits.api import *
> class Child(HasTraits):
>     state = Enum("happy", "sad", "bawling")
>
> class Parent(HasTraits):
>     child = Instance(Child)
>
>     @on_trait_change('child.state')
>     def handler(self):
>         print "new child state:", self.child.state
>
> bob_jr = Child()
> bob = Parent(child = bob_jr)
>
> bob_jr.state = "sad"
> # This would result in bob.handler() being called
>
> (Disclosure: I work at Enthought and have been using Traits heavily
> for the last 4+ years.)
>
> -Peter

I haven't looked at Enthought  in awhile. I want to avoid having to
installing the entire Enthought  toolsuite, however. Would I have to
do that for Traits?

Thanks again.