Re: checking if a list is empty

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From	Ian Kelly <ian.g.kelly@gmail.com>
Date	2011-05-08 22:34 -0600
Subject	Re: checking if a list is empty
Newsgroups	comp.lang.python
Message-ID	<mailman.1321.1304915676.9059.python-list@python.org> (permalink)

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On Sun, May 8, 2011 at 9:33 PM, harrismh777 <harrismh777@charter.net> wrote:
>   Why should the negation of a list imply that the list empty?  ... nor any
> other abstract condition which is not well suited to 'not' ? (forget python
> for a moment... then move on to my argument...)
>
>   What made the python development team (or individual) decide that the
> logical construct   'not list'   would return True if the list is empty?
> To say that "This is the way we do it in Python because Python does it this
> way"---  goes beyond pedantic becoming circular and redundant.
>
>   On the other hand, if you were to tell me *why* you think that the logical
> construct 'not list' should be logically True when the list is empty--- when
> clearly negating a list would not necessarily mean to make the list empty
> (including destroying it)... then you might be seeing my point.

"bool(list)" describes whether the list contains something.  "Not"
being a logical operator, it stands to reason that "not list" should
mean the same thing as "not bool(list)".  Anything else would be
surprising and pointlessly convoluted.  If "not list" bothers you,
then I would suggest that your problem is actually with "bool(list)".

>        ...  should return True only if 'list' is bound to NULL, or if the
> name 'list' would throw a name exception...

Why?  Should "not False" return True only if "False" is bound to NULL
(whatever you mean by that), or if the name "False" would throw a name
exception?

>        ...  and, Python should have an explicit way of testing for an empty
> list that is clear, concise, and easy to understand even for the relatively
> new Python programmer.  This is not intended to generate counter argument,
> its just my feedback on a language construct that I find to be inconsistent
> logically. ... Please, no pedantic discourse explaining why I'm wrong...
> just put in into a PEP and move on.  :)

It does.  "if len(list) == 0"

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Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-06 15:31 -0400
  Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-06 14:49 -0500
    Re: checking if a list is empty Adam Tauno Williams <awilliam@whitemice.org> - 2011-05-06 16:05 -0400
      Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-07 02:49 +0000
        Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 10:14 +0100
          Re: checking if a list is empty Laurent Claessens <moky.math@gmail.com> - 2011-05-11 11:48 +0200
            Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 11:14 +0000
              Re: checking if a list is empty Laurent Claessens <moky.math@gmail.com> - 2011-05-11 13:45 +0200
              Re: checking if a list is empty Laurent Claessens <moky.math@gmail.com> - 2011-05-11 13:45 +0200
          Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 13:36 +0000
            Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 15:00 +0100
              Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 00:46 +1000
              Re: checking if a list is empty Ethan Furman <ethan@stoneleaf.us> - 2011-05-11 08:53 -0700
              RE: checking if a list is empty "Prasad, Ramit" <ramit.prasad@jpmchase.com> - 2011-05-11 13:50 -0400
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 19:15 +0100
                RE: checking if a list is empty "Prasad, Ramit" <ramit.prasad@jpmchase.com> - 2011-05-11 14:59 -0400
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 20:08 +0100
                Re: checking if a list is empty Ethan Furman <ethan@stoneleaf.us> - 2011-05-11 12:17 -0700
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 20:13 +0100
                Re: checking if a list is empty Ian <hobson42@gmail.com> - 2011-05-11 22:02 +0100
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 21:47 +0000
                Re: checking if a list is empty Steven Howe <howe.steven@gmail.com> - 2011-05-11 15:09 -0700
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 17:38 -0500
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 18:12 -0500
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-12 01:07 +0000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 06:21 +0100
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 13:51 +1000
                Re: checking if a list is empty Ethan Furman <ethan@stoneleaf.us> - 2011-05-12 07:02 -0700
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-13 00:13 +1000
              Re: checking if a list is empty Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-12 11:08 +1200
    Re: checking if a list is empty Chris Rebert <clp2@rebertia.com> - 2011-05-06 13:46 -0700
    Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-07 10:51 +1000
    Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-07 08:28 +0000
      Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-07 22:50 -0500
        Re: checking if a list is empty Ethan Furman <ethan@stoneleaf.us> - 2011-05-07 21:57 -0700
          Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 11:47 +0100
            Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 13:45 +0000
              Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 15:34 +0100
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 16:26 +0000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 19:05 +0100
                RE: checking if a list is empty "Prasad, Ramit" <ramit.prasad@jpmchase.com> - 2011-05-11 14:44 -0400
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 20:26 +0100
                Learning new languages (was: checking if a list is empty) Teemu Likonen <tlikonen@iki.fi> - 2011-05-12 06:37 +0300
                Re: checking if a list is empty Chris Torek <nospam@torek.net> - 2011-05-11 19:05 +0000
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 21:42 +0000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 07:23 +0100
                Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-11 10:31 -0600
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 18:46 +0100
            Re: checking if a list is empty "D'Arcy J.M. Cain" <darcy@druid.net> - 2011-05-11 10:33 -0400
              Re: checking if a list is empty Redcat <redcat@catfolks.net> - 2011-05-11 15:31 +0000
              Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 18:44 +0100
              Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 16:24 -0500
                Re: checking if a list is empty alex23 <wuwei23@gmail.com> - 2011-05-11 20:31 -0700
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 22:53 -0500
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-12 06:13 +0000
                Re: checking if a list is empty "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-05-12 10:42 -0700
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-13 14:41 -0500
                Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-13 14:21 -0600
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-13 19:48 -0500
                Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-13 19:52 -0600
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-13 23:47 -0500
                Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-14 00:14 -0600
                Re: checking if a list is empty Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-14 14:32 +1200
                Re: checking if a list is empty Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-14 14:26 +1200
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 07:13 +0100
                Re: checking if a list is empty Ben Finney <ben+python@benfinney.id.au> - 2011-05-12 16:46 +1000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 08:28 +0100
                Re: checking if a list is empty Ben Finney <ben+python@benfinney.id.au> - 2011-05-12 17:37 +1000
                Re: checking if a list is empty "D'Arcy J.M. Cain" <darcy@druid.net> - 2011-05-12 01:49 -0400
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 07:21 +0100
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 22:16 +1000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 13:43 +0100
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 23:20 +1000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-13 09:47 +0100
        Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-08 14:07 +0000
          Re: checking if a list is empty Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-05-08 18:59 +0300
          Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-08 18:41 -0400
          Re: checking if a list is empty Michael Torrie <torriem@gmail.com> - 2011-05-08 21:31 -0600
          Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-08 22:33 -0500
            Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-08 22:34 -0600
              Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-09 16:58 -0500
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-09 23:34 +0000
                Re: checking if a list is empty Ben Finney <ben+python@benfinney.id.au> - 2011-05-10 09:54 +1000
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-09 19:10 -0500
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-09 19:19 -0500
            Re: checking if a list is empty James Mills <prologic@shortcircuit.net.au> - 2011-05-09 14:46 +1000
          Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-08 22:56 -0500
          Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-09 17:30 -0400
          Re: checking if a list is empty Chris Torek <nospam@torek.net> - 2011-05-12 03:49 +0000

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