python's OOP question

Bruno Desthuilliers onurb at xiludom.gro
Tue Oct 17 11:45:57 CEST 2006


neoedmund wrote:
(snip)
> So I can reuse a method freely only if it's worth reusing.
> For the word "inheritance", in some aspect, meanings reuse the super
> class, with the condition: must reuse everything from super class.

Not really. In fact, inheritance *is* a special case of
composition/delegation. A 'child' class is a class that has references
to other classes - it's 'parents' -, and  then attributes that are not
found in the instance or child class are looked up in the parents
(according to mro rules in case of multiple inheritance). And that's all
there is.

> It's lack of a option to select which methods are to be reused.

Methods not redefined in the 'child' class or it's instance are
'reusable'. Now they are only effectively 'reused' if and when called by
client code. So the 'option to select which methods are to be reused' is
mostly up to both the 'child' class and code using it.

> this is something should be improved for general OOP i think.
> So to answer " What is your problem with having the other extra methods
> too ?",
> in real life, a class is not defined so well that any method is needed
> by sub-class. 

Then perhaps is it time to refactor. A class should be a highly cohesive
unit. If you find yourself needing only a specific subset of a class, it
may be time to extract this subset in it's own class. Given Python's
support for both multiple inheritance and composition/delegation, it's
usually a trivial task (unless you already mixed up too many orthogonal
concerns in your base class...).

-- 
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb at xiludom.gro'.split('@')])"



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