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Re: __getattr__ Confusion

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Date Mon, 4 Feb 2013 12:28:43 +1100
Subject Re: __getattr__ Confusion
From Chris Angelico <rosuav@gmail.com>
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Xref csiph.com comp.lang.python:38113

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On Mon, Feb 4, 2013 at 12:08 PM, Saul Spatz <saul.spatz@gmail.com> wrote:
> class ScrolledCanvas(Frame):
>   def __init__(self, master, width, height, bg, cursor):
>     canv = self.canvas = Canvas(self, bg=bg, relief=SUNKEN)
>
>   def __getattr__(self, name):
>     return getattr(self.canvas, name)

Trying to get my head around what you're doing here. Why are you
inheriting Frame, but passing all attribute queries through to the
Canvas? Why not inherit Canvas?

It looks to me like you're going to have some kind of bootstrap
problem no matter how you do it. You're creating a cyclic reference
(you pass self to Canvas), so one way or another, you need to start
the loop.

Dunder methods (like __getattr__) are looked up in the class, not the
instance, so you can't simply set it in the way you describe. I think
your best bet is going to be the "set up a stub, then fill in the
details" method, which is more or less what you're doing (a stubby
__nonzero__).

ChrisA

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Thread

__getattr__ Confusion Saul Spatz <saul.spatz@gmail.com> - 2013-02-03 17:08 -0800
  Re: __getattr__ Confusion Chris Angelico <rosuav@gmail.com> - 2013-02-04 12:28 +1100
  Re: __getattr__ Confusion Terry Reedy <tjreedy@udel.edu> - 2013-02-03 21:47 -0500
  Re: __getattr__ Confusion Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-04 04:35 +0000
    Re: __getattr__ Confusion Saul Spatz <saul.spatz@gmail.com> - 2013-02-04 05:44 -0800
      Re: __getattr__ Confusion Peter Otten <__peter__@web.de> - 2013-02-04 15:15 +0100
        Re: __getattr__ Confusion Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-05 01:46 +1100
        Re: __getattr__ Confusion Saul Spatz <saul.spatz@gmail.com> - 2013-02-04 09:29 -0800
          Re: __getattr__ Confusion Peter Otten <__peter__@web.de> - 2013-02-04 19:23 +0100
          Re: __getattr__ Confusion Chris Angelico <rosuav@gmail.com> - 2013-02-05 12:00 +1100
        Re: __getattr__ Confusion Saul Spatz <saul.spatz@gmail.com> - 2013-02-04 09:29 -0800

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