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Groups > comp.lang.python > #30420

RE: data attributes override method attributes?

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Terry Reedy wrote:
> On 9/25/2012 4:07 PM, Ian Kelly wrote:
> > On Tue, Sep 25, 2012 at 1:58 PM, Terry Reedy <tjreedy@udel.edu> wrote:
> >> On 9/25/2012 11:03 AM, Chris Angelico wrote:
> >>> Instance attributes override (shadow) class attributes.
> >>
> >>
> >> except for (some? all?) special methods
> >
> > Those names are shadowed too.  If you call foo.__len__() and the name
> > is bound on the instance, it will call that function preferentially.
> > It's just that when the special Python machinery calls the method, it
> > skips the instance and goes straight to the class.
> 
> I added "Ian Kelly reminds me that instance.__xxx__ is only skipped by
> the internal machinery and not by direct accesses in user code. In the
> other hand, docs, official or otherwise, are filled with things like
> 'len(a) calls a.__len__', so I think something should be said that
> giving instances special method attributes does not have the effect one
> might expect."
> 
> to the issue.
> 


Just to make sure I am following, if you call
foo.__len__() it goes to the instance code while
if you do len(foo) it will go to class.__len__()?

If so, why? 

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data attributes override method attributes? Jayden <jayden.shui@gmail.com> - 2012-09-25 06:41 -0700
  Re: data attributes override method attributes? alex23 <wuwei23@gmail.com> - 2012-09-25 06:52 -0700
  Re: data attributes override method attributes? Peter Otten <__peter__@web.de> - 2012-09-25 16:08 +0200
    Re: data attributes override method attributes? alex23 <wuwei23@gmail.com> - 2012-09-25 07:11 -0700
      Re: data attributes override method attributes? Peter Otten <__peter__@web.de> - 2012-09-25 16:54 +0200
      Re: data attributes override method attributes? Chris Angelico <rosuav@gmail.com> - 2012-09-26 01:03 +1000
      Re: data attributes override method attributes? Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-09-25 16:54 +0200
      Re: data attributes override method attributes? Terry Reedy <tjreedy@udel.edu> - 2012-09-25 15:58 -0400
      Re: data attributes override method attributes? Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-25 14:07 -0600
      Re: data attributes override method attributes? Terry Reedy <tjreedy@udel.edu> - 2012-09-25 16:18 -0400
      Re: data attributes override method attributes? Terry Reedy <tjreedy@udel.edu> - 2012-09-25 16:34 -0400
      RE: data attributes override method attributes? "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-09-28 18:02 +0000
        Re: data attributes override method attributes? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-29 03:20 +0000
      Re: data attributes override method attributes? Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-28 12:25 -0600
      Re: data attributes override method attributes? Terry Reedy <tjreedy@udel.edu> - 2012-09-28 14:26 -0400
    Re: data attributes override method attributes? Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-25 21:52 +0200
  Re: data attributes override method attributes? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-25 14:12 +0000

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