Need help subclassing Borg

[Steven D'Aprano]

On Sat, 07 May 2005 08:35:21 -0700, wittempj at hotmail.com wrote:

> See mr Martellis comment of 2001/09/06 in mentiond recipe, you then get
> something like this
> 
> -#!/usr/bin/env python
> -class Borg(object):
> -    _shared_state = {}
> -    def __init__(self):
> -        self.__dict__ = self._shared_state
> -
> -class Duck(Borg):
> -    def __init__(self):
> -        super(Duck, self).__init__()
> -        self.__covering = "feathers" # all ducks are feathered

What version of Python are you using? I'm using 2.3.3 and I get this:

py> donald = Duck()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 3, in __init__
TypeError: super() argument 1 must be type, not classobj



>-        self.__covering = "feathers" # all ducks are feathered
>-    def covering(self):
>-        return self.__covering
>-
>-class Rabbit(Borg):
>-    def __init__(self):
>-        super(Rabbit, self).__init__()
>-        self.__covering = "fur" # all rabbits are furry
> -    def covering(self):
> -        return self.__covering

Hmmm... I hate to be ungrateful, but apart from being inelegant, it means
having to write get_attribute() and set_attribute() methods for every
attribute the caller might conceivably use. I'm sure to miss at least one.
*wink*

Either that or muck around with __getattr__ and __setattr__, which is
getting uglier by the minute.

I'm thinking what I might need is a function that generates a Borg-like
class. So I would do something like:

Rabbit = MakeBorgClass()
# Rabbit is now a class implementing shared state
# all instances of Rabbit share the same state
Duck = MakeBorgClass()
# Duck is now a class implementing shared state
# all instances of Duck share the same state
# but instances of Duck do not share state with instances of Rabbit

Problem is, I haven't got the foggiest idea how to implement something
like that. Am I on the right track? Where do I go from here?



Thanks,


Steven.