Diez B. Roggisch wrote:
>>>
>>> I think '__metaclass__ = whatever' affects only the creation of
>>> classes that
>>> would otherwise be old-style classes?
>>
>> Wrong.
>>
>> If you set __metaclass__ = type, every class in that module will be
>> new-style.
>>
>> If you set __metaclass__ = MyClass, and MyClass inherits from <type>, every
>> class in that module will be new-style and have MyClass as a metaclass.
>>
>> The usual way to create new-style classes, inheriting from object or
>> another
>> new-style class, works because if no __metaclass__ is defined, the first
>> base class's class is taken as the metaclass.
>
>
> I was under that impression, too. But this behaves different (py2.4):
[...]
> deets$ python2.4 /tmp/test.py
> (<class '__main__.meta'>, 'OldStyle', (), {'__module__': '__main__'})
> deets$
>
> I was astonished to see that. Any explanation?
Yes. I was wrong, the order of lookup is reversed. This first base class's
class is used before the global __metaclass__.
So what Damjan said is correct: global __metaclass__ is only usable for
classes that don't have bases.
Whether this is desirable is another question...
Georg
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