Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #15635

Re: all() is slow?

Show all headers | View raw

> which implies that getattr(x, 'a!b') should be equivalent to x.a!b

No, it does not. The documentation states equivalence for two
particular values, and there is no way to deduce truth for all cases
from that. In fact, if it _was_ trying to say it was true for any
attribute value, then your example would be proof that the
documentation is incorrect, since CPython breaks that equivalence.

Devin

On Fri, Nov 11, 2011 at 8:18 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> On Thu, 10 Nov 2011 23:35:32 -0500, Devin Jeanpierre wrote:
>
>>> That is patently untrue. If you were implementing namedtuple without
>>> exec, you would still (or at least you *should*) prevent the user from
>>> passing invalid identifiers as attribute names. What's the point of
>>> allowing attribute names you can't actually *use* as attribute names?
>>
>> Then why doesn't Python do this anywhere else? e.g. why can I
>> setattr(obj, 'a#b') when obj is any other mutable type?
>
> That is implementation-specific behaviour and not documented behaviour
> for Python. If you try it in (say) IronPython or Jython, you may or may
> not see the same behaviour.
>
> The docs for getattr state:
>
>    getattr(x, 'foobar') is equivalent to x.foobar
>
>
> which implies that getattr(x, 'a!b') should be equivalent to x.a!b which
> will give a syntax error. The fact that CPython does less validation is
> arguably a bug and not something that you should rely on: it is *not* a
> promise of the language.
>
> As Terry Reedy already mentioned, the namespace used in classes and
> instances are ordinary generic dicts, which don't perform any name
> validation. That's done for speed. Other implementations may use
> namespaces that enforce legal names for attributes, and __slots__ already
> does:
>
>>>> class X(object):
> ...     __slots__ = ['a', 'b!']
> ...
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> TypeError: Error when calling the metaclass bases
>    __slots__ must be identifiers
>
>
> [...]
>> To go off on another tangent, though, I don't really understand how you
>> guys can think this is reasonable, though. I don't get this philosophy
>> of restricting inputs that would otherwise be perfectly valid
>
> But they aren't perfectly valid. They are invalid inputs. Just because
> getattr and setattr in CPython allow you to create attributes with
> invalid names doesn't mean that everything else should be equally as
> slack.
>
>
> --
> Steven
> --
> http://mail.python.org/mailman/listinfo/python-list
>

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

all() is slow? "OKB (not okblacke)" <brenNOSPAMbarn@NObrenSPAMbarn.net> - 2011-11-07 21:00 +0000
  Re: all() is slow? Chris Rebert <clp2@rebertia.com> - 2011-11-07 13:39 -0800
  Re: all() is slow? david vierra <codewarrior0@gmail.com> - 2011-11-07 13:46 -0800
    Re: all() is slow? Chris Angelico <rosuav@gmail.com> - 2011-11-08 09:06 +1100
      Re: all() is slow? Henrik Faber <hfaber@invalid.net> - 2011-11-08 13:09 +0100
        Re: all() is slow? Chris Angelico <rosuav@gmail.com> - 2011-11-08 23:14 +1100
        Re: all() is slow? John Posner <jjposner@optimum.net> - 2011-11-08 17:51 -0500
        Re: all() is slow? Tim Chase <python.list@tim.thechases.com> - 2011-11-08 17:56 -0600
    Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-08 19:44 -0500
      Re: all() is slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-09 02:47 +0000
        Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-09 18:01 -0500
          Re: all() is slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-09 23:11 +0000
            Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-09 20:26 -0500
              Re: all() is slow? alex23 <wuwei23@gmail.com> - 2011-11-09 19:50 -0800
                Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-09 23:40 -0500
                Re: all() is slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-10 07:35 +0000
              Re: all() is slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-10 07:48 +0000
                Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-10 03:51 -0500
                Re: all() is slow? gene heskett <gheskett@wdtv.com> - 2011-11-10 08:20 -0500
                Re: all() is slow? Terry Reedy <tjreedy@udel.edu> - 2011-11-10 14:25 -0500
            Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-09 20:35 -0500
            Re: all() is slow? Ian Kelly <ian.g.kelly@gmail.com> - 2011-11-09 19:10 -0700
            Re: all() is slow? Ethan Furman <ethan@stoneleaf.us> - 2011-11-10 10:43 -0800
            Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-10 15:37 -0500
              Re: all() is slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-10 23:07 +0000
                Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-10 23:35 -0500
                Re: all() is slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-12 01:18 +0000
                Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-13 01:28 -0500
                Re: all() is slow? alex23 <wuwei23@gmail.com> - 2011-11-13 18:50 -0800
                Re: all() is slow? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-11-13 23:48 -0500
              Re: all() is slow? "OKB (not okblacke)" <brenNOSPAMbarn@NObrenSPAMbarn.net> - 2011-11-11 05:40 +0000
            Re: all() is slow? Ian Kelly <ian.g.kelly@gmail.com> - 2011-11-10 14:19 -0700
              Re: all() is slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-10 22:56 +0000
            Re: all() is slow? Ethan Furman <ethan@stoneleaf.us> - 2011-11-10 13:47 -0800
        Re: all() is slow? Chris Angelico <rosuav@gmail.com> - 2011-11-10 10:15 +1100
    Re: all() is slow? Chris Angelico <rosuav@gmail.com> - 2011-11-09 12:19 +1100
    Re: all() is slow? Chris Rebert <clp2@rebertia.com> - 2011-11-08 17:30 -0800
      Re: all() is slow? Hans Mulder <hansmu@xs4all.nl> - 2011-11-09 16:41 +0100
        Re: all() is slow? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-11-09 09:07 -0800
  Re: all() is slow? John Nagle <nagle@animats.com> - 2011-11-09 14:16 -0800
    Re: all() is slow? alex23 <wuwei23@gmail.com> - 2011-11-09 19:52 -0800
    Re: all() is slow? "OKB (not okblacke)" <brenNOSPAMbarn@NObrenSPAMbarn.net> - 2011-11-10 19:35 +0000
  Re: all() is slow? BOOK-AZ <amalguseynov@gmail.com> - 2011-11-15 08:02 -0800

csiph-web