madpython wrote:
> For the pure theory sake and mind expansion i got a question.
> Experimenting with __new__ i found out how to create a singleton.
> class SingleStr(object):
> def __new__(cls,*args,**kwargs):
> instance=cls.__dict__.get('instance')
> if instance:
> return instance
> cls.instance=object.__new__(cls,*args,**kwargs)
> return cls.instance
>
> What if i need to create no more than 5 (for example) instances of a
> class. I guess that would be not much of a problema but there is a
> complication. If one of the instances is garbagecollected I want to be
> able to spawn another instance....
This should help. You didn't really say how to pick the result
if there are duplicates, so I just decided for myself. Read up
on the weakref module, it is your friend in this kind of problem.
import weakref, random
class Limited(any_new_style_class):
_held_instances = weakref.WeakValueDictionary()
_held_limit = 5
def __new__(class_, *args, **kwargs):
if len(class_._held_instances) < class_._held_limit:
# You could go over here if threading is an issue
instance = super(class_, Limited).__new__(
class_, *args, **kwargs)
class_._held_instances[id(instance)] = instance
return instance
return random.choice(class_._held_instances.values())
--Scott David Daniels
[EMAIL PROTECTED]
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