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Re: using __getitem()__ correctly

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From Ben Finney <ben+python@benfinney.id.au>
Newsgroups comp.lang.python
Subject Re: using __getitem()__ correctly
Date Thu, 31 Dec 2015 11:21:59 +1100
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Steven D'Aprano <steve@pearwood.info> writes:

> On Thu, 31 Dec 2015 10:13 am, Ben Finney wrote:
>
> > You may be familiar with other languages where the distinction
> > between “attribute of an object” is not distinct from “item in a
> > dictionary”. Python is not one of those languages; the distinction
> > is real and important.
>
> I'm not sure what distinction you're referring to, can you explain?

Tersely: the relationship between an object and its attributes, is not
the same as the relationship between a dictionary and its items.

> Obviously there is a syntax difference between x.attr and x['key']

Not merely syntax; the attributes of an object are not generally
available as items of the container.

> but attributes *are* items in a dictionary

That's like saying everything in Python is a number: it conflates the
implementation with the semantics.

The distinction between a Python integer and a Python boolean value is
real and important, despite the incidental fact of their both being
implemented as numbers.

> Either the instance __dict__, the class __dict__, or a superclass
> __dict__.

No, I'm not referring to the ‘__dict__’ attribute of an object; I'm
referring to the object itself.

To talk about the attributes of an object ‘foo’ is distinct from talking
about the items in a dictionary ‘foo’. That distinction is real, and
important.

-- 
 \               “… correct code is great, code that crashes could use |
  `\           improvement, but incorrect code that doesn’t crash is a |
_o__)                    horrible nightmare.” —Chris Smith, 2008-08-22 |
Ben Finney

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Thread

using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-30 12:57 +0000
  Re: using __getitem()__ correctly Chris Angelico <rosuav@gmail.com> - 2015-12-31 00:11 +1100
    Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-30 14:40 +0000
      Re: using __getitem()__ correctly Ian Kelly <ian.g.kelly@gmail.com> - 2015-12-30 08:35 -0700
        Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-30 16:58 +0000
          Re: using __getitem()__ correctly Ian Kelly <ian.g.kelly@gmail.com> - 2015-12-30 13:40 -0700
            Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-30 22:54 +0000
              Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-30 22:58 +0000
              Re: using __getitem()__ correctly Ben Finney <ben+python@benfinney.id.au> - 2015-12-31 10:13 +1100
                Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-30 23:18 +0000
                Re: using __getitem()__ correctly Steven D'Aprano <steve@pearwood.info> - 2015-12-31 10:50 +1100
                Re: using __getitem()__ correctly Ben Finney <ben+python@benfinney.id.au> - 2015-12-31 11:21 +1100
                Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-31 11:30 +0000
                Re: using __getitem()__ correctly Ben Finney <ben+python@benfinney.id.au> - 2015-12-31 22:51 +1100
                Re: using __getitem()__ correctly Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-12-31 12:12 +0000
                Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-31 13:39 +0000
                Re: using __getitem()__ correctly Steven D'Aprano <steve@pearwood.info> - 2016-01-01 02:03 +1100
                Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-31 11:17 +0000
                Re: using __getitem()__ correctly Steven D'Aprano <steve@pearwood.info> - 2016-01-01 01:43 +1100
              Re: using __getitem()__ correctly Ian Kelly <ian.g.kelly@gmail.com> - 2015-12-30 17:31 -0700
                Re: using __getitem()__ correctly "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2015-12-31 12:45 +0000

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