On 4/23/08, Ivan Illarionov ([EMAIL PROTECTED]) wrote: >On 24 ???, 07:27, Scott SA <[EMAIL PROTECTED]> wrote: >> I'm using the @classemethod decorator for some convenience methods and for > >It would make sense to separate instance-level and class-level >behaviour with additional 'objects' namespace. e.g. >cookie_recipie.get_ingredients() to get ingredients only for cookie >recipie and RecipieClass.objects.get_ingrendients([....]) to get all >the ingredients.
As mentioned in another reply, my example was a poor representation of what I was tryin to ask. With that said, your reply is amazingly helpful in my quest to understand python, Django, etc. Django is the ORM I referred to, so the material you have written helps explain a few things. >The elegant solution (AFAIK used by Django) would be to use metaclass >and the object with custom descriptor for class-object/table level >stuff. > >Something like this: > >class RecipieMetaclass(type): > def __new__(cls, bases, attrs): > new_cls = type.__new__(cls, name, bases, attrs) > new_cls.objects = IngredientsDescriptor(IngredientsManager()) > return new_cls > >class RecipieClass(object): > __metaclass__ = RecipieMetaclass > def get_ingredients(self, recipie_list=None): > return self.do_something_interesting(recipie_list) > >class IngredientsManager(object): > def get_ingredients(self, recipie_list=None): > return do_something_boring(recipie_list) > >class IngredientsDescriptor(object): > def __init__(self, ingredients_manager): > self.ingredients_manager = ingredients_manager > def __get__(self, instance, type=None): > if instance is not None: > raise AttributeError, "Access via %s instances is not >allowed" % type.__name__ > return self.ingredients_manager > >Then, "at another time, wanting to know what all the ingredients would >be to make cookies, cake and bread" you would call: >RecipieClass.objects.get_ingrendients(['cookies','cake','bread']) I'm a little vague on the interaction of the IngredientsDescrptor VS IngredientsManager. I gather the 'Descriptor' class is called via the __get__ which then does the instance check. Could this have been done in the 'Manager' class? >Both Django and Google Apps Engine API use similar concepts and you >can learn much more interesting looking in their source code. I have been learning a lot from the Django code and other applications written within it. Still, some things just don't seem to gel, even after a host of google searches. I've not loked at the Google Apps stuff, but will follow your advice. Thanks, Scott -- http://mail.python.org/mailman/listinfo/python-list
