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Groups > comp.lang.python > #38466
| Date | 2013-02-08 17:14 +0000 |
|---|---|
| From | MRAB <python@mrabarnett.plus.com> |
| Subject | Re: Implicit conversion to boolean in if and while statements |
| References | (2 earlier) <mailman.2141.1342369188.4697.python-list@python.org> <7b027612-a07e-40f9-8ad2-3e95c5440482@googlegroups.com> <f2b3fa89-d977-4ffd-8861-6a49fcbaf66c@g4g2000pbn.googlegroups.com> <67531902-cccc-4966-8278-b9948818dbde@googlegroups.com> <5114a7b5$0$30003$c3e8da3$5496439d@news.astraweb.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.1515.1360343660.2939.python-list@python.org> (permalink) |
On 2013-02-08 07:22, Steven D'Aprano wrote:
> Rick Johnson wrote:
>
>> Why even have a damn bool function if you're never going to use it?
>
> bool is for converting arbitrary objects into a canonical True or False
> flag. E.g. one use-case is if you wish to record in permanent storage a
> flag, and don't want arbitrary (possibly expensive) objects to be recorded.
>
> Most of the time, you shouldn't care whether you have a canonical True/False
> bool, you should only care whether you have something which duck-types as a
> boolean flag: a truthy or falsey value. In Python, all objects duck-type as
> flags. The usual interpretation is whether the object represents something
> or nothing:
>
> "nothing", or falsey values: None, False, 0, 0.0, '', [], {}, set(), etc.
> (essentially, the empty value for whichever type you are considering)
>
> "something", or truthy values: True, 1, 2.5, 'hello world', etc.
> (essentially, non-empty values).
>
Anything that's not falsey is truey.
> Prior to Python 3, the special method __bool__ was spelled __nonempty__,
> which demonstrates Python's philosophy towards duck-typing bools.
>
Incorrect, it was spelled __nonzero__.
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Re: Implicit conversion to boolean in if and while statements Rick Johnson <rantingrickjohnson@gmail.com> - 2013-02-07 21:53 -0800
Re: Implicit conversion to boolean in if and while statements Chris Angelico <rosuav@gmail.com> - 2013-02-08 17:15 +1100
Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-08 18:22 +1100
Re: Implicit conversion to boolean in if and while statements MRAB <python@mrabarnett.plus.com> - 2013-02-08 17:14 +0000
Re: Implicit conversion to boolean in if and while statements Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-09 09:18 +1100
Re: Implicit conversion to boolean in if and while statements Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-08 09:42 +0000
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