Defining VCL-like framework for Python

[Just van Rossum]

I wrote (off line):
> Do you happen to know where I could read what "environmental acquisition"
> is? Or, if you have a spare minute and the concept happens to be
> explainable in a sentence or two...

David Ascher elaborated:
>There's a URL, but it's gone (temporarily, I'm sure).  Jim gave a talk at
>the DC FedUnix IPC on it, there might be something on www.python.org... .
>(can't find anything detailed).
>
>The idea is that one can set things up so that instances get attributes
>from their parents in a containment (has-a) hierarchy, not just the
>inheritance (is-a) hierarchy.  This makes sense for things like background
>colors in GUI elements, for example -- the color of a widget should by
>default be the color of the parent widget.  That way you change the color
>of the toplevel window, and all subwidgets get that color, except if they
>override it "locally".
>
>Jim has some tools which use ExtensionClasses to make that happen:
>
>>>> class Window(Acquisition.Implicit):
>...    background = 'white'
>...    def __init__(self):
>...       self.menubar = MenuBar()
>...
>>>> class MenuBar(Acquisition.Implicit):
>...   def report(self):
>...     print "self.background =", self.background
>...
>>>> w = Window()
>>>> w.menubar.report()
>self.background = white
>
>It's very cool, somewhat non-trivial to use right (it affects the way one
>designs massively), and requires a fairly deep brain-tweak. Still, worth
>knowing about when designing a new framework where containment is such an
>important notion.  It's one of the few "new" concepts in programming that
>I've seen in the last few years which I think has huge potential for
>simplifying complex designs.

Thanks David, thats very helpful. It's sounds an awful lot like
delegation, but smarter. How do the two concepts relate?

(Barganing for a free CS course ;-)

Just