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Re: checking if a list is empty

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On 5/14/2011 3:39 AM, Steven D'Aprano wrote:

> Th money-quote as regards using arbitrary objects in truth tests:
>
>      [quote]
>      All this changed with the introduction of the two-element
>      boolean domain {true, false} which provides the vocabulary
>      needed to assign values to boolean expressions: 3<4 is a
>      way for writing true, 3>4 is a way for writing false,
>      whereas the value of x>0 depends on the value of x ...
>      [end quote]
>
>
> In Python, [1, 2, 3] is another way of writing true, and [] is another
> way of writing false. Similarly with any other arbitrary objects.

Another way to look at it is that Python automatically calls bool() on 
every expression in its two boolean or conditional contexts: 'if e:' and 
'while e'. This is a boilerplate-removing, labor-saving convenience. 
Python has many such conveniences.

-- 
Terry Jan Reedy

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checking if a list is empty Jabba Laci <jabba.laci@gmail.com> - 2011-05-06 02:36 -0400
  Re: checking if a list is empty Richard Thomas <chardster@gmail.com> - 2011-05-06 03:34 -0700
  Re: checking if a list is empty scattered <tooscattered@gmail.com> - 2011-05-06 14:57 -0700
    Re: checking if a list is empty Philip Semanchuk <philip@semanchuk.com> - 2011-05-06 18:21 -0400
    Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-06 17:51 -0600
      Re: checking if a list is empty Jon Clements <joncle@googlemail.com> - 2011-05-06 17:43 -0700
        Re: checking if a list is empty Hans Mulder <hansmu@xs4all.nl> - 2011-05-14 10:52 +0200
    Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-07 02:51 +0000
      Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 10:02 +0100
        Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 12:14 +0000
          Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 15:05 +0100
            Re: checking if a list is empty "D'Arcy J.M. Cain" <darcy@druid.net> - 2011-05-11 10:27 -0400
              Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 18:59 +0100
                Re: checking if a list is empty alex23 <wuwei23@gmail.com> - 2011-05-11 20:16 -0700
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 06:20 +0100
            Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 15:50 +0000
              Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 02:05 +1000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 18:56 +0100
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 16:13 -0500
          RE: checking if a list is empty "Prasad, Ramit" <ramit.prasad@jpmchase.com> - 2011-05-11 13:39 -0400
        Re: checking if a list is empty Roy Smith <roy@panix.com> - 2011-05-11 08:26 -0400
          Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 13:29 +0000
          Re: checking if a list is empty Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-12 17:44 +1200
            Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 07:06 +0100
            Re: checking if a list is empty Roy Smith <roy@panix.com> - 2011-05-12 07:36 -0400
              Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-13 00:16 +0000
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-12 23:46 -0700
                Re: checking if a list is empty Chris Rebert <clp2@rebertia.com> - 2011-05-13 01:02 -0700
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-13 03:58 -0700
                Re: checking if a list is empty Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-14 14:34 +1200
                Re: checking if a list is empty David Robinow <drobinow@gmail.com> - 2011-05-14 10:28 -0400
                Re: checking if a list is empty Roy Smith <roy@panix.com> - 2011-05-14 11:04 -0400
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-14 07:39 +0000
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-14 00:45 -0700
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-14 23:42 +1000
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-14 08:47 -0700
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-15 01:55 +1000
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-14 10:43 -0700
                Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-14 17:29 -0400
                Re: checking if a list is empty Ben Finney <ben+python@benfinney.id.au> - 2011-05-15 09:26 +1000
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-14 19:41 -0700
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-15 05:07 +0000
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-15 10:33 -0700
                Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-15 17:36 -0400
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-15 22:56 -0700
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-16 00:36 +0000
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-15 20:59 -0500
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-15 22:40 -0700
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-15 20:25 -0500
                Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-15 21:57 -0400
                Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-14 16:59 -0400
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-15 05:00 +0000
                Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-14 16:53 -0400
          Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-12 15:37 -0400
          Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-12 18:00 -0400
  Re: checking if a list is empty Raymond Hettinger <python@rcn.com> - 2011-05-06 15:52 -0700

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