What is the semantics meaning of 'object'?

[Adam Jiang]

> * 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