> * 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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