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

Groups > comp.lang.python > #73008

Re: Uniform Function Call Syntax (UFCS)

Path csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From Marko Rauhamaa <marko@pacujo.net>
Newsgroups comp.lang.python
Subject Re: Uniform Function Call Syntax (UFCS)
Date Mon, 09 Jun 2014 09:25:33 +0300
Organization A noiseless patient Spider
Lines 42
Message-ID <874mzu1twi.fsf@elektro.pacujo.net> (permalink)
References <8b96ae27-20fa-4df9-807e-c806fed983c0@googlegroups.com> <mailman.10859.1402169265.18130.python-list@python.org> <bvhsgeF2on9U2@mid.individual.net> <38058e64-0113-457c-ae63-cc66e8b569cd@googlegroups.com> <mailman.10876.1402229177.18130.python-list@python.org> <8738ff2y4g.fsf@elektro.pacujo.net> <53953912$0$29988$c3e8da3$5496439d@news.astraweb.com>
Mime-Version 1.0
Content-Type text/plain; charset=us-ascii
Injection-Info mx05.eternal-september.org; posting-host="ff5cf27ef3d5b31f034d3b72bdc27a41"; logging-data="29550"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19Rtp4bGYeNFBUlnnDpyxOR"
User-Agent Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux)
Cancel-Lock sha1:KGX15yw0xig4IrLz4u3uM86WAsc= sha1:zaMxtx0hil+3w3ztu7Y8j8DcrwY=
Xref csiph.com comp.lang.python:73008

Show key headers only | View raw

Steven D'Aprano <steve+comp.lang.python@pearwood.info>:

> On Sun, 08 Jun 2014 18:56:47 +0300, Marko Rauhamaa wrote:
>> In fact, what's the point of having the duality?
>>    x < y <==> x.__lt__(y)
>
> [...]
>
> Consider x + y. What happens?
>
> #1 First, Python checks whether y is an instance of a *subclass* of x. If 
> so, y gets priority, otherwise x gets priority.
>
> #2 If y gets priority, y.__radd__(x) is called, if it exists. If it 
> returns something other than NotImplemented, we are done.
>
> #3 However if y.__radd__ doesn't exist, or it returns NotImplemented, 
> then Python continues as if x had priority.
>
> #3 If x has priority, then x.__add__(y) is called, if it exists. If it 
> returns something other than NotImplemented, we are done. 
>
> #4 However if it doesn't exist, or it returns NotImplemented, then 
> y.__radd__(x) is called, provided it wasn't already tried in step #2.
>
> #5 Finally, if neither object has __add__ or __radd__, or both return 
> NotImplemented, then Python raises TypeError.

In a word, Python has predefined a handful of *generic
functions/methods*, which are general and standard in GOOPS (Guile's
object system):

   (define-method (+ (x <string>) (y <string)) ...)
   (define-method (+ (x <matrix>) (y <matrix>)) ...)
   (define-method (+ (f <fish>) (b <bicycle>)) ...)
   (define-method (+ (a <foo>) (b <bar>) (c <baz>)) ...)

   <URL: http://www.gnu.org/software/guile/manual/html_node/
   Methods-and-Generic-Functions.html>


Marko

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

Thread

Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-06 23:45 -0700
  Re: Uniform Function Call Syntax (UFCS) Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-07 13:20 -0600
    Re: Uniform Function Call Syntax (UFCS) Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-06-08 13:27 +1200
      Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-08 01:26 -0700
        Re: Uniform Function Call Syntax (UFCS) Paul Sokolovsky <pmiscml@gmail.com> - 2014-06-08 15:06 +0300
          Re: Uniform Function Call Syntax (UFCS) Marko Rauhamaa <marko@pacujo.net> - 2014-06-08 18:56 +0300
            Re: Uniform Function Call Syntax (UFCS) Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-08 10:38 -0600
            Re: Uniform Function Call Syntax (UFCS) Paul Sokolovsky <pmiscml@gmail.com> - 2014-06-08 19:40 +0300
            Re: Uniform Function Call Syntax (UFCS) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-09 04:33 +0000
              Re: Uniform Function Call Syntax (UFCS) Marko Rauhamaa <marko@pacujo.net> - 2014-06-09 09:25 +0300
                Re: Uniform Function Call Syntax (UFCS) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-09 09:09 +0000
                Re: Uniform Function Call Syntax (UFCS) Chris Angelico <rosuav@gmail.com> - 2014-06-09 19:13 +1000
                Re: Uniform Function Call Syntax (UFCS) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-09 13:37 +0000
                Re: Uniform Function Call Syntax (UFCS) Chris Angelico <rosuav@gmail.com> - 2014-06-10 01:08 +1000
          Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-08 09:24 -0700
            Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-08 09:34 -0700
            Re: Uniform Function Call Syntax (UFCS) Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-08 10:54 -0600
            Re: Uniform Function Call Syntax (UFCS) Chris Angelico <rosuav@gmail.com> - 2014-06-09 03:10 +1000
              Re: Uniform Function Call Syntax (UFCS) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-09 03:20 +0000
                Re: Uniform Function Call Syntax (UFCS) Chris Angelico <rosuav@gmail.com> - 2014-06-09 13:44 +1000
                Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-08 23:38 -0700
                Re: Uniform Function Call Syntax (UFCS) Roy Smith <roy@panix.com> - 2014-06-08 23:45 -0400
      Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-08 02:25 -0700
        Re: Uniform Function Call Syntax (UFCS) Roy Smith <roy@panix.com> - 2014-06-08 10:59 -0400
          Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-08 08:39 -0700
            Re: Uniform Function Call Syntax (UFCS) Chris Angelico <rosuav@gmail.com> - 2014-06-09 02:48 +1000
              Re: Uniform Function Call Syntax (UFCS) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-09 03:53 +0000
                Re: Uniform Function Call Syntax (UFCS) Chris Angelico <rosuav@gmail.com> - 2014-06-09 14:53 +1000
                Re: Uniform Function Call Syntax (UFCS) Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-09 08:24 -0600
                Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-09 23:43 -0700
            Re: Uniform Function Call Syntax (UFCS) Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-08 11:08 -0600
            Re: Uniform Function Call Syntax (UFCS) Chris Angelico <rosuav@gmail.com> - 2014-06-09 03:13 +1000
            Re: Uniform Function Call Syntax (UFCS) Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-08 11:24 -0600
              Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-08 13:35 -0700
    Re: Uniform Function Call Syntax (UFCS) jongiddy <jongiddy@gmail.com> - 2014-06-08 01:15 -0700
      Re: Uniform Function Call Syntax (UFCS) Paul Sokolovsky <pmiscml@gmail.com> - 2014-06-08 14:52 +0300
      Re: Uniform Function Call Syntax (UFCS) Ian Kelly <ian.g.kelly@gmail.com> - 2014-06-08 11:00 -0600

csiph-web