ClassName.attribute vs self.__class__.attribute
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....
> 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
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.
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