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
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