ClassName.attribute vs self.__class__.attribute

Gabriel Rossetti gabriel.rossetti at arimaz.com
Fri Jun 6 12:19:39 CEST 2008


Larry Bates wrote:
> Gabriel Rossetti wrote:
>> Hello everyone,
>>
>> I had read somewhere that it is preferred to use 
>> self.__class__.attribute over ClassName.attribute to access class 
>> (aka static) attributes. I had done this and it seamed to work, until 
>> I subclassed a class using this technique and from there on things 
>> started screwing up. I finally tracked it down to 
>> self.__class__.attribute! What was happening is that the child 
>> classes each over-rode the class attribute at their level, and the 
>> parent's was never set, so while I was thinking that I had indeed a 
>> class attribute set in the parent, it was the child's that was set, 
>> and every child had it's own instance! Since it was a locking 
>> mechanism, lots of fun to debug... So, I suggest never using 
>> self.__class__.attribute, unless you don't mind it's children 
>> overriding it, but if you want a truly top-level class attribute, use 
>> ClassName.attribute everywhere!
>>
>> I wish books and tutorials mentioned this explicitly....
>>
>> Gabriel
>
> If you define a class instance variable with the same name as the 
> class attribute, how would Python be able to distinguish the two?  
> That is a feature not a problem.  Getter looks for instance attribute, 
> if one is not found it looks for a class attribute, and upwards.  This 
> behavior is used by Zope to do all sorts of neat stuff.
>
> -Larry Bates
> -- 
> http://mail.python.org/mailman/listinfo/python-list
>
>
A class instance variable, you must mean an instance attribute no? If 
that is so, then with just self.attribute? Maybe there is a concept that 
I don't know about, I've studied class/static attributes and instance 
attributes in my OOP classes.

Gabriel



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