Re: Alias for an attribute defined in a superclass

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From	Ben Finney <ben+python@benfinney.id.au>
Newsgroups	comp.lang.python
Subject	Re: Alias for an attribute defined in a superclass
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Date	Fri, 01 Apr 2011 11:59:47 +1100
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Steven D'Aprano <steve+comp.lang.python@pearwood.info> writes:

> On Fri, 01 Apr 2011 09:14:03 +1100, Ben Finney wrote:
>
> > I want to inherit from a class, and define aliases for many of its
> > attributes.
>
> Are these aliases of arbitrary aliases, or only of methods, as in your
> example below?

I'd like to know how to do either, for making API wrapper classes.

> > How can I refer to “the attribute that will be available by
> > name ‘spam’ once this class is defined”?
>
> You might be able to use the descriptor protocol to do something like
> that, but otherwise I don't think you can. However, I note that your
> example isn't *quite* how you describe it above.

Yes, I got the names wrong. The example is accurate to what I'm meaning
to say.

> >     class Foo(object):
> >         def spam(self):
> >             pass
> >         def eggs(self):
> >             pass
> > 
> >     class Bar(Foo):
> >         beans = Foo.spam
> >         mash = Foo.eggs
>
> This assigns the name Bar.beans to the method object Foo.spam. If you
> now rebind the name Foo.spam to something else, Bar.beans will not
> likewise change, but will continue to refer to the original. This is
> contrary to your earlier description, where Bar.beans should also
> change.

Hmm. I think I can live with that limitation.

> > Is that the right way to do it? Will that leave me open to “unbound
> > method” or “is not an instance of ‘Bar’” or other problems when
> > using ‘Bar.beans’?
>
> I don't believe so. So long as you don't rebind the "alias" or the 
> original, you should be fine.

Okay, thank you.

-- 
 \      “I am too firm in my consciousness of the marvelous to be ever |
  `\       fascinated by the mere supernatural …” —Joseph Conrad, _The |
_o__)                                                     Shadow-Line_ |
Ben Finney

Thread

Alias for an attribute defined in a superclass Ben Finney <ben+python@benfinney.id.au> - 2011-04-01 09:14 +1100
  Re: Alias for an attribute defined in a superclass Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-01 00:14 +0000
    Re: Alias for an attribute defined in a superclass Ben Finney <ben+python@benfinney.id.au> - 2011-04-01 11:59 +1100
  Re: Alias for an attribute defined in a superclass Calvin Spealman <ironfroggy@gmail.com> - 2011-03-31 20:36 -0400
    Re: Alias for an attribute defined in a superclass Ben Finney <ben+python@benfinney.id.au> - 2011-04-01 11:57 +1100
  Re: Alias for an attribute defined in a superclass Raymond Hettinger <python@rcn.com> - 2011-03-31 19:24 -0700
    Re: Alias for an attribute defined in a superclass Jean-Michel Pichavant <jeanmichel@sequans.com> - 2011-04-01 11:54 +0200

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