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Groups > comp.lang.python > #103870
| From | Marko Rauhamaa <marko@pacujo.net> |
|---|---|
| Newsgroups | comp.lang.python |
| Subject | Re: Explaining names vs variables in Python |
| Date | 2016-03-02 16:11 +0200 |
| Organization | A noiseless patient Spider |
| Message-ID | <87povdt1ec.fsf@elektro.pacujo.net> (permalink) |
| References | (2 earlier) <56d6c146$0$1615$c3e8da3$5496439d@news.astraweb.com> <87y4a1t5wj.fsf@elektro.pacujo.net> <mailman.100.1456923030.20602.python-list@python.org> <87twkpt2w7.fsf@elektro.pacujo.net> <mailman.101.1456926519.20602.python-list@python.org> |
Chris Angelico <rosuav@gmail.com>:
> On Thu, Mar 3, 2016 at 12:39 AM, Marko Rauhamaa <marko@pacujo.net> wrote:
>> Chris Angelico <rosuav@gmail.com>:
>>
>>> Python defines that every object has an identity, which can be
>>> represented as an integer. Since this is an intrinsic part of the
>>> object, no two distinct objects can truly have identical
>>> characteristics. Python's objects are like rifles - there are many
>>> like it, but this one is mine.
>>
>> How can you be sure Python isn't returning the same id value for two
>> distinct objects?
>
> The same way I can be sure about anything else in Python. It's a
> language guarantee.
Actually, my question is (intentionally) nonsensical.
The sameness or distinctness of two objects is not directly defined in
Python. The definition is simply:
Two objects X and Y are called identical if
X is Y
evaluates to a true value.
Additionally, we have:
If objects X and Y are identical, it is guaranteed that
id(X) == id(Y)
evaluates to a true value.
Even more strongly, we have:
For any objects X and Y,
id(X) == id(Y) if X is Y else id(X) != id(Y)
evaluates to a true value.
What is missing is the rules that are obeyed by the "is" operator.
Marko
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Explaining names vs variables in Python Salvatore DI DIO <salvatore.didio@gmail.com> - 2016-03-02 00:32 -0800
Re: Explaining names vs variables in Python Jesper K Brogaard <jesper@brogAAaard.eu> - 2016-03-02 10:03 +0100
Re: Explaining names vs variables in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-02 21:32 +1100
Re: Explaining names vs variables in Python Marko Rauhamaa <marko@pacujo.net> - 2016-03-02 14:34 +0200
Re: Explaining names vs variables in Python Chris Angelico <rosuav@gmail.com> - 2016-03-02 23:50 +1100
Re: Explaining names vs variables in Python Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-03-02 15:11 +0200
Re: Explaining names vs variables in Python Marko Rauhamaa <marko@pacujo.net> - 2016-03-02 15:39 +0200
Re: Explaining names vs variables in Python Chris Angelico <rosuav@gmail.com> - 2016-03-03 00:48 +1100
Re: Explaining names vs variables in Python Marko Rauhamaa <marko@pacujo.net> - 2016-03-02 16:11 +0200
Re: Explaining names vs variables in Python Rustom Mody <rustompmody@gmail.com> - 2016-03-02 07:08 -0800
Re: Explaining names vs variables in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-03 04:23 +1100
Re: Explaining names vs variables in Python Rustom Mody <rustompmody@gmail.com> - 2016-03-02 09:28 -0800
Re: Explaining names vs variables in Python Marko Rauhamaa <marko@pacujo.net> - 2016-03-02 20:12 +0200
Re: Explaining names vs variables in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-03 12:52 +1100
Re: Explaining names vs variables in Python Rustom Mody <rustompmody@gmail.com> - 2016-03-03 09:03 -0800
Re: Explaining names vs variables in Python Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-03 12:53 -0700
Re: Explaining names vs variables in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-02 21:49 +0000
Re: Explaining names vs variables in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-03 13:05 +1100
Re: Explaining names vs variables in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-03 16:09 +0000
Re: Explaining names vs variables in Python Chris Angelico <rosuav@gmail.com> - 2016-03-03 08:52 +1100
Re: Explaining names vs variables in Python Rustom Mody <rustompmody@gmail.com> - 2016-03-02 17:23 -0800
Re: Explaining names vs variables in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-02 22:51 +0000
Re: Explaining names vs variables in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-03 04:10 +1100
Re: Explaining names vs variables in Python Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2016-03-02 10:08 +0100
Effects of caching frequently used objects, was Re: Explaining names vs variables in Python Peter Otten <__peter__@web.de> - 2016-03-02 10:12 +0100
Re: Explaining names vs variables in Python Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-03-02 11:35 +0200
Re: Explaining names vs variables in Python Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-02 08:13 -0700
Re: Explaining names vs variables in Python Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-03-02 17:37 +0200
Re: Explaining names vs variables in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-02 21:16 +1100
Re: Explaining names vs variables in Python "ast" <nomail@invalid.com> - 2016-03-02 11:52 +0100
Re: Explaining names vs variables in Python Salvatore DI DIO <salvatore.didio@gmail.com> - 2016-03-02 02:58 -0800
Re: Effects of caching frequently used objects, was Re: Explaining names vs variables in Python Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-03-02 09:16 -0500
Re: Explaining names vs variables in Python Ben Finney <ben+python@benfinney.id.au> - 2016-03-03 04:53 +1100
RE: Effects of caching frequently used objects, was Re: Explaining names vs variables in Python Albert-Jan Roskam <sjeik_appie@hotmail.com> - 2016-03-25 13:03 +0000
Re: Effects of caching frequently used objects, was Re: Explaining names vs variables in Python Chris Angelico <rosuav@gmail.com> - 2016-03-26 00:22 +1100
Re: Effects of caching frequently used objects, was Re: Explaining names vs variables in Python Ethan Furman <ethan@stoneleaf.us> - 2016-03-25 09:45 -0700
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