Re: Equivalent code to the bool() built-in function

From	Duncan Booth <duncan.booth@invalid.invalid>
Newsgroups	comp.lang.python
Subject	Re: Equivalent code to the bool() built-in function
Date	2011-04-18 10:01 +0000
Message-ID	<Xns9ECB701D0C11Fduncanbooth@127.0.0.1> (permalink)
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Steven D'Aprano <steve+comp.lang.python@pearwood.info> wrote:

> So in Python 2.2, Python introduced two new built-in names, True and 
> False, with values 1 and 0 respectively:
> 
> [steve@sylar ~]$ python2.2
> Python 2.2.3 (#1, Aug 12 2010, 01:08:27)
> [GCC 4.1.2 20070925 (Red Hat 4.1.2-27)] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>>>> True, False
> (1, 0)
>>>> type(True)
><type 'int'>
> 

Also in Python 2.2 (and I think earlier but I don't have anything 
earlier to check) there was an interesting property that while all other 
integers from -1 to 99 were optimised to share a single instance, there 
were actually 2 instances of 0 and 1:

Python 2.2.3 (#1, Sep 26 2006, 18:12:26)
[GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-56)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 2-1 is 1
1
>>> True is 1
0
>>> (True is 1) is 0
0
>>> (True is 1) is False
1

The code for the win32api made use of this fact to determine whether to 
pass int or bool types through to COM methods.

-- 
Duncan Booth http://kupuguy.blogspot.com

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Equivalent code to the bool() built-in function candide <candide@free.invalid> - 2011-04-16 22:24 +0200
  Re: Equivalent code to the bool() built-in function Chris Rebert <clp2@rebertia.com> - 2011-04-16 13:58 -0700
    Re: Equivalent code to the bool() built-in function Ben Finney <ben+python@benfinney.id.au> - 2011-04-17 07:38 +1000
      Re: Equivalent code to the bool() built-in function candide <candide@free.invalid> - 2011-04-17 01:51 +0200
        Re: Equivalent code to the bool() built-in function Chris Rebert <clp2@rebertia.com> - 2011-04-16 17:16 -0700
        Re: Equivalent code to the bool() built-in function Ben Finney <ben+python@benfinney.id.au> - 2011-04-17 12:39 +1000
          Re: Equivalent code to the bool() built-in function candide <candide@free.invalid> - 2011-04-17 10:38 +0200
            Re: Equivalent code to the bool() built-in function Chris Angelico <rosuav@gmail.com> - 2011-04-17 18:46 +1000
              Re: Equivalent code to the bool() built-in function Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-04-18 12:12 +1200
                Re: Equivalent code to the bool() built-in function John Nagle <nagle@animats.com> - 2011-04-18 12:58 -0700
                Re: Equivalent code to the bool() built-in function Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-04-19 12:18 +1200
                Re: Equivalent code to the bool() built-in function Christian Heimes <lists@cheimes.de> - 2011-04-19 03:39 +0200
                Re: Equivalent code to the bool() built-in function Kushal Kumaran <kushal.kumaran+python@gmail.com> - 2011-04-19 11:53 +0530
                Re: Equivalent code to the bool() built-in function Grant Edwards <invalid@invalid.invalid> - 2011-04-19 14:23 +0000
                Re: Equivalent code to the bool() built-in function Jean-Paul Calderone <calderone.jeanpaul@gmail.com> - 2011-04-19 08:43 -0700
                Re: Equivalent code to the bool() built-in function Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-04-20 11:59 +1200
                Re: Equivalent code to the bool() built-in function Chris Angelico <rosuav@gmail.com> - 2011-04-19 16:26 +1000
                Re: Equivalent code to the bool() built-in function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-19 08:43 +0000
                Re: Equivalent code to the bool() built-in function Chris Angelico <rosuav@gmail.com> - 2011-04-19 19:00 +1000
                Re: Equivalent code to the bool() built-in function Westley Martínez <anikom15@gmail.com> - 2011-04-19 06:43 -0700
            Re: Equivalent code to the bool() built-in function Ben Finney <ben+python@benfinney.id.au> - 2011-04-17 19:46 +1000
              Re: Equivalent code to the bool() built-in function candide <candide@free.invalid> - 2011-04-18 01:22 +0200
                Re: Equivalent code to the bool() built-in function Ben Finney <ben+python@benfinney.id.au> - 2011-04-18 09:46 +1000
                Re: Equivalent code to the bool() built-in function Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-04-18 12:08 +1200
                Re: Equivalent code to the bool() built-in function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-18 00:22 +0000
                Re: Equivalent code to the bool() built-in function Chris Angelico <rosuav@gmail.com> - 2011-04-18 10:52 +1000
                Re: Equivalent code to the bool() built-in function Duncan Booth <duncan.booth@invalid.invalid> - 2011-04-18 10:01 +0000
            Re: Equivalent code to the bool() built-in function Daniel Kluev <dan.kluev@gmail.com> - 2011-04-17 21:11 +1100
      Re: Equivalent code to the bool() built-in function Daniel Kluev <dan.kluev@gmail.com> - 2011-04-18 10:45 +1100
        Re: Equivalent code to the bool() built-in function Ben Finney <ben+python@benfinney.id.au> - 2011-04-18 10:36 +1000
      Re: Re: Equivalent code to the bool() built-in function Chris Angelico <rosuav@gmail.com> - 2011-04-18 11:52 +1000
      Re: Re: Equivalent code to the bool() built-in function Dave Angel <davea@ieee.org> - 2011-04-17 21:46 -0400
      Re: Re: Equivalent code to the bool() built-in function Daniel Kluev <dan.kluev@gmail.com> - 2011-04-18 14:16 +1100
      Re: Equivalent code to the bool() built-in function Ned Deily <nad@acm.org> - 2011-04-17 21:40 -0700
      Re: Equivalent code to the bool() built-in function Chris Angelico <rosuav@gmail.com> - 2011-04-18 14:53 +1000
        Re: Equivalent code to the bool() built-in function Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-04-19 12:22 +1200
      Re: Equivalent code to the bool() built-in function Chris Rebert <clp2@rebertia.com> - 2011-04-17 22:49 -0700
        Re: Equivalent code to the bool() built-in function Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-18 06:14 +0000
      Re: Equivalent code to the bool() built-in function Chris Angelico <rosuav@gmail.com> - 2011-04-18 16:03 +1000
  Re: Equivalent code to the bool() built-in function Ben Finney <ben+python@benfinney.id.au> - 2011-04-17 07:13 +1000
    Re: Equivalent code to the bool() built-in function candide <candide@free.invalid> - 2011-04-17 01:51 +0200
  Re: Equivalent code to the bool() built-in function Raymond Hettinger <python@rcn.com> - 2011-04-18 01:33 -0700
    Re: Equivalent code to the bool() built-in function candide <candide@free.invalid> - 2011-04-18 11:19 +0200

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