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Re: What is the semantics meaning of 'object'?

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Date Sun, 23 Jun 2013 22:35:46 +0900
From Adam Jiang <jiang.adam@gmail.com>
To python-list@python.org
Subject Re: What is the semantics meaning of 'object'?
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Xref csiph.com comp.lang.python:48980

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> * property only works in "new-style" classes that inherit from object;
> 
> * likewise for super;

Another question raised here is that what is the proper way to refer
to parent class? For example,

class A(object):
        def __init__(self, arg):
                print "A"

class B(A):
        def __init__(self, arg):
                super(B, self).__init__(arg)

Is this correct? As the result, whenever you wanted to refer to a
method in parent class, super() functions has to be called. This seems
inefficient.

How to refer to a field defined in parent class?

Thanks,
/Adam

>On Sun, Jun 23, 2013 at 03:20:02AM +0000, Steven D'Aprano wrote:
> On Sat, 22 Jun 2013 19:58:38 -0700, Adam wrote:
> 
> > class FooBar(object):
> >     def __init__(self):
> >         ...
> > 
> > Inheritance usually takes a class name to indicate which class is the
> > 'parent' class. However, in the previous example, from a django book,
> > the class actually takes an 'object' like parameter, doesn't it? What is
> > the semantics meaning of such kind of notation?
> 
> It's not merely notation, "object" is the name of a class. If you type it 
> (without quotes) at the interactive interpreter, you will see it is a 
> built-in class:
> 
> py> object
> <class 'object'>
> 
> 
> In Python 3, the use of object as base class is optional, but in Python 2 
> there is a subtle difference between classes that inherit from object and 
> those that don't. The reason for this difference is buried in the mists 
> of time, going back to Python 2.2. If you are interested, google on 
> "Python unifying types and classes":
> 
> https://duckduckgo.com/html/?q=Python+unifying+types+and+classes
> 
> 
> As a general rule, unless you actually want "old-style class" behaviour, 
> you should always inherit from object (or some other built-in type) in 
> Python 2. In Python 3, it doesn't matter.
> 
> The differences include:
> 
> * property only works in "new-style" classes that inherit from object;
> 
> * likewise for super;
> 
> * multiple inheritance with old-style classes can be buggy;
> 
> * new-style classes may be slightly faster in general;
> 
> * on the down side, automatic delegation of special double-underscore 
> methods like __getitem__ and __str__ doesn't work with new-style classes.
> 
> 
> If none of this means anything to you, be glad, and just inherit from 
> object or some other built-in type in all your classes, and all will be 
> good.
> 
> 
> 
> 
> -- 
> Steven
> -- 
> http://mail.python.org/mailman/listinfo/python-list

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Thread

What is the semantics meaning of 'object'? Adam <jiang.adam@gmail.com> - 2013-06-22 19:58 -0700
  Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-23 03:20 +0000
    Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-22 22:27 -0600
      Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-23 05:23 +0000
        Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-22 23:40 -0600
          Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-23 17:29 +0000
            Re: What is the semantics meaning of 'object'? Rotwang <sg552@hotmail.co.uk> - 2013-06-24 02:53 +0100
              Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-24 06:31 +0000
                Re: What is the semantics meaning of 'object'? Rotwang <sg552@hotmail.co.uk> - 2013-06-24 16:00 +0100
                Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-24 11:23 -0600
    Re: What is the semantics meaning of 'object'? Adam Jiang <jiang.adam@gmail.com> - 2013-06-23 22:35 +0900
    Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-23 10:15 -0600
      Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-23 16:35 +0000
        Re: What is the semantics meaning of 'object'? Roy Smith <roy@panix.com> - 2013-06-23 12:49 -0400
          Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-23 11:08 -0600
            Re: What is the semantics meaning of 'object'? Roy Smith <roy@panix.com> - 2013-06-23 14:14 -0400
          Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-23 11:18 -0600
            Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-23 17:36 +0000
              Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-23 12:04 -0600
                Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-23 18:50 +0000
                Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-23 13:09 -0600
                Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-24 01:12 +0000
                Re: What is the semantics meaning of 'object'? Roy Smith <roy@panix.com> - 2013-06-23 15:24 -0400
                Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-24 01:27 +0000
                Re: What is the semantics meaning of 'object'? Roy Smith <roy@panix.com> - 2013-06-23 21:38 -0400
                Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-24 08:06 +0000
                Re: What is the semantics meaning of 'object'? Roy Smith <roy@panix.com> - 2013-06-24 08:41 -0400
                Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-24 08:58 -0700
                Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-24 23:51 +0000
                Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-24 11:26 -0600
                Re: What is the semantics meaning of 'object'? Ethan Furman <ethan@stoneleaf.us> - 2013-06-26 13:14 -0700
                Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-26 23:54 +0000
                Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-26 19:03 -0600
                Re: What is the semantics meaning of 'object'? Ethan Furman <ethan@stoneleaf.us> - 2013-06-26 17:38 -0700
          Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-23 18:46 +0000
            Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-23 13:05 -0600
            Re: What is the semantics meaning of 'object'? Ethan Furman <ethan@stoneleaf.us> - 2013-06-26 13:37 -0700
          Re: What is the semantics meaning of 'object'? Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-23 13:33 -0700
        Re: What is the semantics meaning of 'object'? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-06-23 21:33 +0200
        Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-25 11:44 -0600
        Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-25 14:58 -0700
        Re: What is the semantics meaning of 'object'? Chris Angelico <rosuav@gmail.com> - 2013-06-26 08:17 +1000
        Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-25 16:21 -0600
        Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-25 16:25 -0600
        Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-25 15:29 -0700
        Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-25 15:27 -0700
        Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-25 15:38 -0700
        Re: What is the semantics meaning of 'object'? Chris Angelico <rosuav@gmail.com> - 2013-06-26 08:39 +1000
        Re: What is the semantics meaning of 'object'? Chris Angelico <rosuav@gmail.com> - 2013-06-26 08:47 +1000
        Re: What is the semantics meaning of 'object'? Chris Angelico <rosuav@gmail.com> - 2013-06-26 08:57 +1000
          Re: What is the semantics meaning of 'object'? Rotwang <sg552@hotmail.co.uk> - 2013-06-26 16:16 +0100
            Re: What is the semantics meaning of 'object'? Chris Angelico <rosuav@gmail.com> - 2013-06-27 01:23 +1000
        Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-25 17:07 -0600
        Re: What is the semantics meaning of 'object'? Chris Angelico <rosuav@gmail.com> - 2013-06-26 09:08 +1000
        Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-25 17:10 -0600
        Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-25 16:19 -0700
          Re: What is the semantics meaning of 'object'? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-26 08:36 +0000
          Re: What is the semantics meaning of 'object'? alex23 <wuwei23@gmail.com> - 2013-06-28 10:19 +1000
            Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-28 11:55 -0700
        Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-25 16:00 -0700
        Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-25 18:19 -0600
        Re: What is the semantics meaning of 'object'? Mark Janssen <dreamingforward@gmail.com> - 2013-06-25 18:07 -0700
        Re: What is the semantics meaning of 'object'? Chris Angelico <rosuav@gmail.com> - 2013-06-26 17:25 +1000
        Re: What is the semantics meaning of 'object'? Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-26 02:53 -0600
        Re: What is the semantics meaning of 'object'? Chris Angelico <rosuav@gmail.com> - 2013-06-26 09:54 +1000
        Re: What is the semantics meaning of 'object'? Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-06-26 12:56 +0200
      Re: What is the semantics meaning of 'object'? Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-23 13:12 -0700

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