Re: checking if a list is empty

References	<BANLkTikF18n2dBU6hhFngcAPkE2ZpErVAw@mail.gmail.com> <BANLkTimWdAijp6vWm9sC_9rFMgpoRf35Hg@mail.gmail.com> <mailman.1260.1304710333.9059.python-list@python.org> <9hYwp.5805$xo2.3333@newsfe07.iad> <1304712309.9905.10.camel@linux-yu4c.site>
Date	2011-05-07 10:51 +1000
Subject	Re: checking if a list is empty
From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.1279.1304729507.9059.python-list@python.org> (permalink)

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On Sat, May 7, 2011 at 6:05 AM, Adam Tauno Williams
<awilliam@whitemice.org> wrote:
> On Fri, 2011-05-06 at 14:49 -0500, harrismh777 wrote:
>> Terry Reedy wrote:
>> >>> (2) if not li:
>> >> This is fine.
>> > This is the intended way. Anything in addition is extra noise and wasted
>> > calculation. In other words, let Python do the boilerplate work for you.
>>     I agree, but I don't like it.
>
> +1  This is the Python reality-distortion-field at work.
>
> Motto#1: Python is all about readability!
> Motto#2: Crytic code is awesome if it is Pythoncally cryptic!

As a C and C++ programmer, I probably shouldn't offer an opinion, but
it is quite normal in C++ to compare objects for truth/falseness - for
instance, stream objects return false on error/eof, so you can
efficiently code a loop with "while (infile) {...}". Not to mention
that the nullness of a C string (a PSZ) is quite happily and safely
tested by seeing if the pointer is true (non-null) or false (null).

That said, though, readability is a relative thing. A construct is
transparently obvious if it does something in the exact same way that
it's always been done, no matter how obscure it was the first time.
Why is it, for instance, that putting two short strokes perpendicular
to one another indicates addition? Yet if you see the construct "x +
y", you know exactly what it means - it's readable, it's not cryptic
at all. People assume and expect that this compact syntax will be
available, and object heavily to such notation as "add(x,y)" which
says exactly what it does.

if not li:

is perfectly readable; you just need a comprehension of what truth
means for a list.

Chris Angelico

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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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