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Re: __dict__ attribute for built-in types

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candide <candide@free.invalid> writes:

> Le 28/10/2011 00:57, Hrvoje Niksic a écrit :
>
>> was used at class definition time to suppress it.  Built-in and
>> extension types can choose whether to implement __dict__.
>>
>
> Is it possible in the CPython implementation to write something like this :
>
> "foo".bar = 42
>
> without raising an attribute error ?

No, and for good reason.  Strings are immutable, so that you needn't
care which particular instance of "foo" you're looking at, they're all
equivalent.  The interpreter uses that fact to cache instances of short
strings such as Python identifiers, so that most places that look at a
string like "foo" are in fact dealing with the same instance.  If one
could change an attribute of a particular instance of "foo", it would no
longer be allowed for the interpreter to transparently cache them.  The
same goes for integers and other immutable built-in objects.

If you really need to attach state to strings, subclass them as Steven
explained.  All code that accepts strings (including all built-ins) will
work just fine, transparent caching will not happen, and attributes are
writable.

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__dict__ attribute for built-in types candide <candide@free.invalid> - 2011-10-27 12:08 +0200
  Re: __dict__ attribute for built-in types Arnaud Delobelle <arnodel@gmail.com> - 2011-10-27 11:36 +0100
  Re: __dict__ attribute for built-in types Duncan Booth <duncan.booth@invalid.invalid> - 2011-10-27 11:03 +0000
    Re: __dict__ attribute for built-in types Chris Angelico <rosuav@gmail.com> - 2011-10-28 00:25 +1100
      Re: __dict__ attribute for built-in types Duncan Booth <duncan.booth@invalid.invalid> - 2011-10-27 14:36 +0000
        Re: __dict__ attribute for built-in types Chris Angelico <rosuav@gmail.com> - 2011-10-28 09:39 +1100
    Re: __dict__ attribute for built-in types candide <candide@free.invalid> - 2011-10-27 16:01 +0200
      Re: __dict__ attribute for built-in types Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-10-27 22:19 +0000
        Re: __dict__ attribute for built-in types candide <candide@free.invalid> - 2011-10-28 00:52 +0200
          Re: __dict__ attribute for built-in types Terry Reedy <tjreedy@udel.edu> - 2011-10-27 22:44 -0400
          Re: __dict__ attribute for built-in types alex23 <wuwei23@gmail.com> - 2011-10-27 19:48 -0700
          Re: __dict__ attribute for built-in types Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-10-28 08:01 +0000
            Re: __dict__ attribute for built-in types candide <candide@free.invalid> - 2011-10-28 12:03 +0200
            Re: __dict__ attribute for built-in types Christian Heimes <lists@cheimes.de> - 2011-10-28 13:51 +0200
          Re: __dict__ attribute for built-in types Peter Pearson <ppearson@nowhere.invalid> - 2011-10-28 15:52 +0000
      Re: __dict__ attribute for built-in types Hrvoje Niksic <hniksic@xemacs.org> - 2011-10-28 00:57 +0200
        Re: __dict__ attribute for built-in types candide <candide@free.invalid> - 2011-10-28 01:36 +0200
          Re: __dict__ attribute for built-in types MRAB <python@mrabarnett.plus.com> - 2011-10-28 01:02 +0100
            Re: __dict__ attribute for built-in types candide <candide@free.invalid> - 2011-10-28 04:46 +0200
              Re: __dict__ attribute for built-in types Patrick Maupin <pmaupin@gmail.com> - 2011-10-27 20:02 -0700
                Re: __dict__ attribute for built-in types candide <candide@free.invalid> - 2011-10-28 12:04 +0200
          Re: __dict__ attribute for built-in types Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-10-28 06:21 +0000
          Re: __dict__ attribute for built-in types Hrvoje Niksic <hniksic@xemacs.org> - 2011-10-28 11:08 +0200
            Re: __dict__ attribute for built-in types candide <candide@free.invalid> - 2011-10-28 12:23 +0200
  Re: __dict__ attribute for built-in types Nobody <nobody@nowhere.com> - 2011-10-28 06:49 +0100

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