should I put old or new style classes in my book?

[Arnaud Delobelle]

Alan Isaac <aisaac at american.edu> writes:

> This thread raises two questions for me.
>
> 1. I take it from this thread that in Python 3 the following are
> equivalent:
>
>        class Test: pass
>
>        class Test(object): pass
>
> Is that correct, and if so, where is it stated explicitly?
> (I know about the "all classes are new style classes" statement.)

I don't know where it is stated, but how could they *not* be
equivalent?

> 2. I take it from this thread that in Python 2.2+ if I put the
> following at the top of a module ::
>
>        __metaclass__ = type
>
> then all the classes defined in that module will be newstyle
> classes.  Is that correct?  Somehow I did not grok that from
>
> <URL:http://docs.python.org/ref/metaclasses.html>
>
> but it seems right.

>From the URL you quote:

    The appropriate metaclass is determined by the following
    precedence rules:

    * If dict['__metaclass__'] exists, it is used.

    * Otherwise, if there is at least one base class, its metaclass is
      used (this looks for a __class__ attribute first and if not
      found, uses its type).

    * Otherwise, if a global variable named __metaclass__ exists, it
      is used.

    * Otherwise, the old-style, classic metaclass (types.ClassType) is
      used.

Look at the third point.

-- 
Arnaud