On Sep 7, 10:27 am, Carsten Haese <[EMAIL PROTECTED]> wrote:
> On Fri, 2007-09-07 at 12:31 +0000, André wrote:
> > In my application, I make use of the Borg idiom, invented by Alex
> > Martelli.
>
> > class Borg(object):
> > '''Borg Idiom, from the Python Cookbook, 2nd Edition, p:273
>
> > Derive a class form this; all instances of that class will share
> > the
> > same state, provided that they don't override __new__; otherwise,
> > remember to use Borg.__new__ within the overriden class.
> > '''
> > _shared_state = {}
> > def __new__(cls, *a, **k):
> > obj = object.__new__(cls, *a, **k)
> > obj.__dict__ = cls._shared_state
> > return obj
>
> > ----
> > This has worked very well so far, but is starting to impose some
> > unwanted constraints on my program design.
>
> > What I would like to do is, to put it figuratively, create a Borg
> > rebellion with various splinter groups. In concrete Python terms, I
> > would like to have
>
> > class MyClass(Borg, ...):
> > ...
>
> > seven_of_nine = MyClass(...) # part of group "BORG"
> > two_of_nine = MyClass(...)
>
> > splinter1 = MyClass(..., group='splinter')
> > splinter2 = MyClass(..., group='splinter')
>
> > and have splinter 1 and splinter2 share the same state, but a
> > different state than the one shared by members of the BORG collective.
>
> > Any suggestions from the metaclass experts?
>
> You don't need a metaclass. Just turn _shared_state into a dictionary of
> shared states, keyed by the group name:
>
> class SplinterBorg(object):
> _shared_states = {}
> def __new__(cls, *a, **k):
> group = k.pop("group","BORG")
> obj = object.__new__(cls, *a, **k)
> obj.__dict__ = cls._shared_states.setdefault(group,{})
> return obj
>
> HTH,
>
> --
> Carsten Haesehttp://informixdb.sourceforge.net
Unfortunately, it fails. Here's what I tried, followed by the
traceback
class SplinterBorg(object):
_shared_states = {}
def __new__(cls, *a, **k):
group = k.pop("group","BORG")
obj = object.__new__(cls, *a, **k)
obj.__dict__ = cls._shared_states.setdefault(group,{})
return obj
class MyClass(SplinterBorg):
def __init__(self, name):
self.name = name
a1 = MyClass('a')
a2 = MyClass('aa')
b1 = MyClass('b', group="B")
Traceback (most recent call last):
File "test.py", line 15, in <module>
b1 = MyClass('b', group="B")
TypeError: __init__() got an unexpected keyword argument 'group'
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