list property fires get on append

[Soviut]

On Jan 6, 11:36 am, Carl Banks <pavlovevide... at gmail.com> wrote:
> On Sun, 06 Jan 2008 00:31:13 -0800, Soviut wrote:
> > I figured that an append would be treated as a set since I'm adding to
> > the list.  But what you say makes sense, although I can't say I'm happy
> > with the behaviour.  Is there any way I can get the append to fire a
> > set?  I'm thinking of properties from my C# background where i believe
> > that manipulation such this would be considered a set.
>
> You'd have to have to hook into the container object itself to detect the
> modification.  This might be pretty workable for you since it's an
> internal object.  Basically, instead of using a list, use a special list-
> like object that notifies it's owner when it changes.  Here's a simple
> example to point you in the right direction:
>
> class NotifierList(list):
>      def __init__(self,*args,**kwargs):
>          super(NotifierList,self).__init__(*args,**kwargs)
>          self.watchers = []
>      def add_watcher(self,watcher):
>          self.watchers.append(watcher)
>      def _notify_watchers(self):
>          for watcher in self.watchers:
>              watcher.object_changed(self)
>      def append(self,value):
>          super(NotifierList,self).append(value)
>          self._notify_watchers()
>      # override all other mutating calls, including __setitem__
>      # left as exercise
>
> class Hierarchy(object):
>     def __init__(self):
>         self.children = NotifierList()
>         self.children.add_watcher(self)
>     def object_changed(self,obj):
>         print "self.children modified"
>     # no need to make children a property then
>     # unless you want to trap rebinding it to new object also
>
> A couple other minor suggestions:
>
> print is a statement, not a function.  You should write
>
> print "GETTING"
>
> not
>
> print("GETTING")
>
> The latter works, but it will cease to work if you want to print more
> than one thing.  Note that print is scheduled to become a function in
> Python 3.0, but for now it's a statement.
>
> Based on the name of your class and typical usage, I'm guessing that you
> probably want _children to be an instance attribute rather than a class
> attribute, so I redid it that way, but .)
>
> P.S. Is calling a method called "firing" in C#?
>
> Carl Banks

I just want to thank you for the example.  I implemented the
NotifierList class and modified it to suite my project.  It works
great.  Thanks again.