[Edu-sig] Topics for CS2

Scott David Daniels Scott.Daniels at Acm.Org
Fri Jan 23 01:14:29 CET 2009

Scott David Daniels wrote:
I wrote:

> In PythonOOP.doc (page 4) you say:
>  > There are two pieces of "magic" that make line 3 work.  First, the
>  > interpreter has to find the method set_vars.  It's not in cat2.  Then,
>  > the instance cat2 has to be inserted as the first argument to et_vars.
>  > The method is found by a search starting at cat2 ( the instance on
>  > which the method is called ).  The search then proceeds to the parent
>  > class, then to the grandparent, and so on up to object, the ancestor
>  > of all Animal classes.  In this case, we find set_vars in Cat.
> For instances of subclasses of object (such as Cat), method lookups
> start in Cat, not cat2.  If you try to set cat2.set_vars, you cannot
> (because a method is a property stored in he class), and you will try
> the set method of that property which will fail.  Simple class variables
> are over-ridden by assignments to the instance values, but properties
> are not.

And then immediately went to make a test case, which failed.  Which
I should, of course, done before hitting send.  I retract my comment
and will get back to you when I get my understanding straightened out.

--Scott David Daniels
Scott.Daniels at Acm.Org

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