Dynamic subclassing ?

[manatlan]

On 13 mai, 01:24, a... at mac.com (Alex Martelli) wrote:
> manatlan <manat... at gmail.com> wrote:
> > I've got an instance of a class, ex :
>
> > b=gtk.Button()
>
> > I'd like to add methods and attributes to my instance "b".
> > I know it's possible by hacking "b" with setattr() methods. But i'd
> > like to do it with inheritance, a kind of "dynamic subclassing",
> > without subclassing the class, only this instance "b" !
>
> > In fact, i've got my instance "b", and another class "MoreMethods"
>
> > class MoreMethods:
> >     def  sayHello(self):
> >           print "hello"
>
> > How could i write ...
>
> > "b = b + MoreMethods"
>
> > so "b" will continue to be a gtk.Button, + methods/attributs of
> > MoreMethods (it's what i call "dynamic inheritance") ...so, things
> > like this should work :
>
> > - b.set_label("k")
> > - b.sayHello()
>
> > I can't find the trick, but i'm pretty sure it's possible in an easy
> > way.
>
> I think what you're asking for is totally weird, and with just about
> zero advantages compared with several saner alternatives that have
> already been proposed in this thread and that you have rejects, but
> sure, it's possible:
>
> def addaclass(aninst, onemoreclass):
>     aninst.__class__ = type(aninst.__aclass__.__name__,
>             (aninst.__aclass__, onemoreclass), {})
>
> Alex

I know it's weird ... and solutions given here are a lot saner. But i
can't do that at the creation of the instance, because it's not me who
has the creation process ... the only things i've got, it's the
instance

i tried :

class MoreMethods:
    def  sayHello(self):
        print "hello"

def addaclass(aninst, onemoreclass):
    aninst.__class__ = type(aninst.__class__.__name__,
            (aninst.__class__, onemoreclass), {})

b=gtk.Button("the_label")
addaclass(b,MoreMethods)
print b.get_label()
print b.hello()

but got :
"TypeError: __class__ assignment: only for heap types"
on the last line ...

I begin to think that the only solution is to use the module new like
Karlo said ...