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

Groups > comp.lang.python > #83437

Re: Comparisons and sorting of a numeric class....

Show all headers | View raw

On Fri, Jan 9, 2015 at 11:27 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> Chris Kaynor wrote:
>
>> Lately, I've been doing quite a bit of work in lua, and many times have
>> wished that empty strings, tables, and 0 acted "falsey", but at the same
>> time, previously working in Python, there were plenty of times I wished
>> they acted "truthy". It merely depends on what algorithm I am using at the
>> time...
>
>
> Please do elaborate. I've never found myself in a situation where I have
> wanted empty containers to be truthy, and I can't think of what such a
> situation would be like.

It's a matter of what you're comparing against. If you might have a
thing and might not, the obvious way to arrange things is to have the
thing be true and the non-thing be false. That works nicely if that
"thing" is an object that's always True, and the "non-thing" is None;
for instance, I might have a socket object, and I might not, so I can
use "if not self.socket: self.connect()" to ensure that I have one
(assuming that self.connect() will throw an error if it fails to
establish, blah blah, handwave away the details). This does NOT work
if a socket object might be false, so I'd have to explicitly check "if
self.socket is None:". Similarly, there are times when the user might
have entered a string or might not - say you have an optional
parameter "--name" which, if omitted, defaults to some sort of
arbitrarily-assigned name; to distinguish between "--name=" and not
providing that parameter at all, the logical way is to have name be
either a string or None. Again, "if name" would make good sense as
meaning "if the --name parameter was provided", rather than "if the
--name parameter was provided and not the empty string". If it helps,
think of a "nullable field" in databasing.

Python's truthiness model is pretty consistent (apart from a few
oddities like midnight being false), so I'm not advocating making this
change. I'm just explaining the case where the opposite choice does
make sense.

ChrisA

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

Thread

Re: Comparisons and sorting of a numeric class.... Andrew Robinson <andrew3@r3dsolutions.com> - 2015-01-06 18:01 -0800
  Re: Comparisons and sorting of a numeric class.... Steven D'Aprano <steve@pearwood.info> - 2015-01-07 08:10 +0000
    Re: Comparisons and sorting of a numeric class.... Chris Angelico <rosuav@gmail.com> - 2015-01-07 19:21 +1100
    Re: Comparisons and sorting of a numeric class.... Marko Rauhamaa <marko@pacujo.net> - 2015-01-07 12:01 +0200
      Re: Comparisons and sorting of a numeric class.... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-08 10:46 +1100
        Re: Comparisons and sorting of a numeric class.... Marko Rauhamaa <marko@pacujo.net> - 2015-01-08 08:21 +0200
          Re: Comparisons and sorting of a numeric class.... Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-08 07:57 -0700
            Re: Comparisons and sorting of a numeric class.... Marko Rauhamaa <marko@pacujo.net> - 2015-01-08 21:41 +0200
          Re: Comparisons and sorting of a numeric class.... Chris Kaynor <ckaynor@zindagigames.com> - 2015-01-08 10:44 -0800
            Re: Comparisons and sorting of a numeric class.... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-09 23:27 +1100
              Re: Comparisons and sorting of a numeric class.... Chris Angelico <rosuav@gmail.com> - 2015-01-09 23:43 +1100
                Re: Comparisons and sorting of a numeric class.... Marko Rauhamaa <marko@pacujo.net> - 2015-01-09 16:28 +0200
                Re: Comparisons and sorting of a numeric class.... Paul Rubin <no.email@nospam.invalid> - 2015-01-09 07:06 -0800
                Re: Comparisons and sorting of a numeric class.... Chris Angelico <rosuav@gmail.com> - 2015-01-10 02:14 +1100
                Re: Comparisons and sorting of a numeric class.... Marko Rauhamaa <marko@pacujo.net> - 2015-01-09 17:16 +0200

csiph-web