CONSTRUCT - Adding Functionality to the Overall System

Steve Holden steve at holdenweb.com
Mon Sep 18 14:23:07 CEST 2006


Ilias Lazaridis wrote:
> Damjan wrote:
> 
>>>>I understand that I can use __metaclass__ to create a class which
>>>>modifies the behaviour of another class.
>>>>
>>>>How can I add this metaclass to *all* classes in the system?
>>>>
>>>>(In ruby I would alter the "Class" class)
>>>
>>>You'd have to set
>>>
>>>__metaclass__ = whatever
>>>
>>>at the top of each module whose classes are to get the new behavior.
>>
>>I think '__metaclass__ = whatever' affects only the creation of classes that
>>would otherwise be old-style classes?
> 
> 
> It seems so:
> 
> http://mail.python.org/pipermail/python-list/2003-June/166572.html
> 
> 
>>>You can't alter classes which you don't control or create in your code.
>>
>>I remeber I've seen an implementation of import_with_metaclass somewhere on
>>IBM's developerworks. I didn't quite undersntad it though.
> 
> 
> http://www-128.ibm.com/developerworks/linux/library/l-pymeta.html
> 
> I am not so much interested in old-style, as is start production with
> python 2.4 (possibly even with python 2.5).
> 
The fact remains that you won't be able to affect the built-in classes 
such as int and str - they are hard-coded in C (for CPython, at least), 
and so their metaclass is also implied and cannot be changed.

regards
  Steve
-- 
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