python's OOP question

neoedmund neoedmund at gmail.com
Tue Oct 17 05:00:47 CEST 2006



On Oct 16, 9:01 pm, Bruno Desthuilliers <o... at xiludom.gro> wrote:
> neoedmund wrote:
> > Bruno Desthuilliers wrote:
> >> neoedmund wrote:
> >> (*PLEASE* stop top-posting - corrected)
> >>> Ben Finney wrote:
> >>>> [Please don't top-post above the text to which you're replying.]
>
> >>>> "neoedmund" <neoedm... at gmail.com> writes:
>
> >>>>> I'm trying to achieve a higher level of "reusability". Maybe it
> >>>>> cannot be done in python? Can anybody help me?
> >>>> What, specifically, are you trying to achieve? What problem needs
> >>>> solving?
> >>> python use multiple inheritance.
> >>> but "inheritance" means you must inherite all methods from super type.
> >>> now i just need "some" methods from one type and "some" methods from
> >>> other types, to build the new type.
> >>> Do you think this way is more flexible than tranditional inheritance?
>
> >> While dynamically adding attributes (and methods - which are attributes
> >> too) is not a problem, I'd second Gregor's anwser : it might be better
> >> to use composition/delegation here.
>
> > Could you show some code to help me know how composition/delegation can
> > be done here? Thanks.About composition/delegation, there's no "one-size-fits-all" answer, but
> the main idea is to use the magic '__getattr__(self, name)' method.
>
> Now back to your specific case : after a better reading of your original
> question, straight composition/delegation wouldn't work here - at least
> not without modifications to both C1 and C2 (sorry, should have read
> better the first time).
>
> Given the context (ie : "create a new type with methods from type X and
> methods from type Y"), a very simple solution could be:
>
> class C3(object):
>     m = C2.m.im_func
>     v = C1.v.im_func
>
> FWIW, if you have full control over C1, C2 and C3, you could also just
> 'externalize' the functions definitions:
>
> def v1(self, o):
>     return "expected "+o
>
> def v2(self, o):
>     return "unexpected "+o
>
> def m2(self):
>     """ requires that 'self' has a v(self, somestring) method """
>     print self.v("aaa")
>
> class C1(object):
>     v = v1
>
> class C2(object):
>     v = v2
>     m = m2
>
> class C3(object):
>     v = v1
>     m = m2
>
> The problem (with the whole approach, whatever the choosen technical
> solution) is that if one of theses methods depends on another one (or on
> any other attribute) that is not defined in your new class, you're in
> trouble. This is not such a big deal in the above example, but might
> become much more brittle in real life.
>
> Now we can look at the problem from a different perspective. You wrote:
> """
> but "inheritance" means you must inherite all methods from super type.
> now i just need "some" methods from one type and "some" methods from
> other types, to build the new type.
> """
>
> What is your problem with having the other extra methods too ?
>
> --
> bruno desthuilliers
> python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
> p in 'on... at xiludom.gro'.split('@')])"

Bruno , your 2 great and clear samples revealed what method is in
python, which is also I really want to ask. thank you.
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.
It's lack of a option to select which methods are to be reused.
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. so contains a method never to be used is meaningless and
i think something should forbidden.
also, any handy methods in a class can be grabbed out for our reuse. so
we can forgotting the bundering inheritance tree and order.




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