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Re: Implicit conversion to boolean in if and while statements

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Date Tue, 17 Jul 2012 00:19:48 -0500
From Andrew Berg <bahamutzero8825@gmail.com>
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Subject Re: Implicit conversion to boolean in if and while statements
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On 7/16/2012 11:39 PM, Steven D'Aprano wrote:
> If you need three (or four, or fifty) 
> distinguishable states, then obviously boolean context will not solve 
> your problem. I never said it would.
That is the impression I got from this statement:

> How you interpret some_variable = None depends on what some_variable 
> represents. If some_variable represents "number of jelly beans in a jar", 
> then that should be 0 if there is no jar.
But I guess you misunderstood (or were just picking at) the example.

Of course I can (and do) explicitly use "if x is not None" when testing
for None, but I don't want a bug being obscured because "if x" accepts
an erroneous value that it interprets as truthy or falsey. I could be
explicit when testing for things other than None, but apparently that's
un-Pythonic.

To put it in duck-typing terms, why should everything have to quack like
True or False? Sure, I can see why 1 quacks like True or [] quacks like
False, but I don't see why say, a Logger or function should quack like
either. Should a Thread object be True if it's been started and False
otherwise?

If it truly is about something vs. nothing, why is a NameError (or
AttributeError) raised when testing with an undefined variable? Being
undefined quacks like nothing, doesn't it?
-- 
CPython 3.3.0b1 | Windows NT 6.1.7601.17803

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Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-15 03:34 -0500
  Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-15 10:56 +0000
    Re: Implicit conversion to boolean in if and while statements Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-15 10:19 -0600
      Re: Implicit conversion to boolean in if and while statements Rick Johnson <rantingrickjohnson@gmail.com> - 2012-07-15 09:50 -0700
        Re: Implicit conversion to boolean in if and while statements Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-15 12:01 -0600
          Re: Implicit conversion to boolean in if and while statements Rick Johnson <rantingrickjohnson@gmail.com> - 2012-07-15 11:56 -0700
            Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-16 07:53 +1000
              Re: Implicit conversion to boolean in if and while statements Ranting Rick <rantingrickjohnson@gmail.com> - 2012-07-15 18:21 -0700
                Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-16 11:51 +1000
                Re: Implicit conversion to boolean in if and while statements Ranting Rick <rantingrickjohnson@gmail.com> - 2012-07-15 19:31 -0700
                Re: Implicit conversion to boolean in if and while statements Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-16 17:57 +0000
                Re: Implicit conversion to boolean in if and while statements Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-17 00:44 -0400
                Re: Implicit conversion to boolean in if and while statements Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-15 22:15 -0400
                Re: Implicit conversion to boolean in if and while statements Ranting Rick <rantingrickjohnson@gmail.com> - 2012-07-15 19:58 -0700
                Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-16 04:03 +0000
                Re: Implicit conversion to boolean in if and while statements Ranting Rick <rantingrickjohnson@gmail.com> - 2012-07-15 21:53 -0700
                Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-16 15:57 +1000
                Re: Implicit conversion to boolean in if and while statements alex23 <wuwei23@gmail.com> - 2012-07-16 00:21 -0700
                Re: Implicit conversion to boolean in if and while statements Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-17 00:18 -0400
                Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 06:25 +0000
                Re: Implicit conversion to boolean in if and while statements Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-17 05:38 -0400
                Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-16 02:58 +0000
                Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-16 13:05 +1000
                Re: Implicit conversion to boolean in if and while statements Ranting Rick <rantingrickjohnson@gmail.com> - 2012-07-15 20:21 -0700
                Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-16 04:20 +0000
                Re: Implicit conversion to boolean in if and while statements Ranting Rick <rantingrickjohnson@gmail.com> - 2012-07-15 22:03 -0700
                Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-16 16:00 +1000
                Re: Implicit conversion to boolean in if and while statements alex23 <wuwei23@gmail.com> - 2012-07-16 00:27 -0700
                Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-16 07:52 +0000
                Re: Implicit conversion to boolean in if and while statements Laszlo Nagy <gandalf@shopzeus.com> - 2012-07-16 23:26 +0200
                Re: Implicit conversion to boolean in if and while statements Laszlo Nagy <gandalf@shopzeus.com> - 2012-07-16 23:17 +0200
                Re: Implicit conversion to boolean in if and while statements Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-16 07:30 +0100
                Re: Implicit conversion to boolean in if and while statements Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-16 18:03 +0000
          Re: Implicit conversion to boolean in if and while statements Rick Johnson <rantingrickjohnson@gmail.com> - 2012-07-15 11:56 -0700
        Re: Implicit conversion to boolean in if and while statements Serhiy Storchaka <storchaka@gmail.com> - 2012-07-16 16:01 +0300
        Re: Implicit conversion to boolean in if and while statements rusi <rustompmody@gmail.com> - 2012-07-16 18:45 -0700
      Re: Implicit conversion to boolean in if and while statements Rick Johnson <rantingrickjohnson@gmail.com> - 2012-07-15 09:50 -0700
      Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-16 02:13 +0000
        Re: Implicit conversion to boolean in if and while statements Ranting Rick <rantingrickjohnson@gmail.com> - 2012-07-15 19:41 -0700
          Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-16 12:58 +1000
          Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-16 08:05 +0000
        Re: Implicit conversion to boolean in if and while statements Ethan Furman <ethan@stoneleaf.us> - 2012-07-16 11:13 -0700
          Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 06:14 +0000
    Re: Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-15 12:02 -0500
      Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-16 02:38 +0000
        Re: Implicit conversion to boolean in if and while statements Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-16 13:28 -0400
          Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 01:12 +0000
            Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 01:13 +0000
        Re: Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-16 15:33 -0500
        Re: Implicit conversion to boolean in if and while statements Ethan Furman <ethan@stoneleaf.us> - 2012-07-16 13:54 -0700
          Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 00:43 +0000
            Re: Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-16 20:57 -0500
              Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 04:39 +0000
                Re: Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-17 00:19 -0500
                Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 07:08 +0000
                Re: Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-17 03:23 -0500
                Re: Implicit conversion to boolean in if and while statements alex23 <wuwei23@gmail.com> - 2012-07-17 18:35 -0700
                Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-17 18:32 +1000
                Re: Implicit conversion to boolean in if and while statements Laszlo Nagy <gandalf@shopzeus.com> - 2012-07-17 14:43 +0200
                Re: Implicit conversion to boolean in if and while statements Laszlo Nagy <gandalf@shopzeus.com> - 2012-07-17 14:59 +0200
                Re: Implicit conversion to boolean in if and while statements Terry Reedy <tjreedy@udel.edu> - 2012-07-17 13:57 -0400
                Re: Implicit conversion to boolean in if and while statements Ethan Furman <ethan@stoneleaf.us> - 2012-07-17 05:35 -0700
            Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-17 12:13 +1000
    Re: Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-15 12:16 -0500
    Re: Implicit conversion to boolean in if and while statements Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-15 11:45 -0600
    Re: Implicit conversion to boolean in if and while statements Terry Reedy <tjreedy@udel.edu> - 2012-07-15 16:09 -0400
    Re: Implicit conversion to boolean in if and while statements Terry Reedy <tjreedy@udel.edu> - 2012-07-15 16:28 -0400
    Re: Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-16 20:22 -0500
      Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 04:11 +0000
        Re: Implicit conversion to boolean in if and while statements Ranting Rick <rantingrickjohnson@gmail.com> - 2012-07-16 21:18 -0700
          Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2012-07-17 14:24 +1000
        Re: Implicit conversion to boolean in if and while statements Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-16 23:44 -0500
    Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-17 04:47 +0000
  Re: Implicit conversion to boolean in if and while statements John Nagle <nagle@animats.com> - 2012-07-17 00:26 -0700

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