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Re: Interesting list() un-optimization

References (2 earlier) <loom.20130307T121601-338@post.gmane.org> <CALwzid=wNNBa6Mnx0sr84N1+PiZHMHtra7iQHg_2pYDpsd4kig@mail.gmail.com> <khaep0$qst$1@ger.gmane.org> <CALwzidnpNK7w6gL8Pk1VqBdEFRXUuTdTyyPpOisNeMVpPLuWEg@mail.gmail.com> <khap77$a95$1@ger.gmane.org>
From Ian Kelly <ian.g.kelly@gmail.com>
Date 2013-03-07 13:26 -0700
Subject Re: Interesting list() un-optimization
Newsgroups comp.lang.python
Message-ID <mailman.3051.1362688062.2939.python-list@python.org> (permalink)

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On Thu, Mar 7, 2013 at 12:19 PM, Stefan Behnel <stefan_ml@behnel.de> wrote:
>> Didn't know about that, thanks.  Presumably a proper iter(QuerySet())
>> object could implement __length_hint__ in an efficient manner rather
>> than by just calling the __len__ of the underlying QuerySet,
>
> And how exactly would it do that, without either doing what __len__ does or
> reading the whole result set into memory?

If the underlying cursor provides its own efficient length hint, it
could return that.  Or if the query is result-limited, use the limit
as a length hint, provided it's not absurdly large.  And if you really
can't efficiently determine anything about the length of the result
set at all, you can always fall back on returning NotImplemented.

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Thread

Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-06 22:20 -0500
  Re: Interesting list() un-optimization Dave Angel <davea@davea.name> - 2013-03-06 22:38 -0500
  Re: Interesting list() un-optimization Tim Chase <python.list@tim.thechases.com> - 2013-03-06 21:57 -0600
  Re: Interesting list() un-optimization Kev Dwyer <kevin.p.dwyer@gmail.com> - 2013-03-07 07:31 +0000
  Re: Interesting list() un-optimization Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2013-03-07 11:22 +0000
  Re: Interesting list() un-optimization Ian Kelly <ian.g.kelly@gmail.com> - 2013-03-07 09:00 -0700
  Re: Interesting list() un-optimization Christian Heimes <christian@python.org> - 2013-03-07 17:20 +0100
  Re: Interesting list() un-optimization Ian Kelly <ian.g.kelly@gmail.com> - 2013-03-07 10:31 -0700
  Re: Interesting list() un-optimization Stefan Behnel <stefan_ml@behnel.de> - 2013-03-07 20:19 +0100
  Re: Interesting list() un-optimization Ian Kelly <ian.g.kelly@gmail.com> - 2013-03-07 13:26 -0700
  Re: Interesting list() un-optimization Terry Reedy <tjreedy@udel.edu> - 2013-03-07 15:29 -0500
  Re: Interesting list() un-optimization Terry Reedy <tjreedy@udel.edu> - 2013-03-07 15:34 -0500
  Re: Interesting list() un-optimization Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2013-03-07 20:41 +0000
  Re: Interesting list() un-optimization Terry Reedy <tjreedy@udel.edu> - 2013-03-07 17:53 -0500
  Re: Interesting list() un-optimization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-08 17:59 +0000
    Re: Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-08 13:45 -0500
  Re: Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-10 09:05 -0400
    Re: Interesting list() un-optimization Terry Reedy <tjreedy@udel.edu> - 2013-03-10 17:39 -0400
      Re: Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-10 18:34 -0400
        Re: Interesting list() un-optimization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-10 23:35 +0000
          Re: Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-10 19:50 -0400

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