<[EMAIL PROTECTED]> writes:
> 1) New instance has to have a property called 'name'
> 2) When instance is attemped to created, e.g., x=kls(name='myname'), and
> there already exists an instance with obj.name =='myname', that
> pre-existing instance is returned, instead of making new one.
> 3) A class property 'all' for class gives me a list of all the
> instances. So kls.all lets me iterates through all instances.
> 4) When all the hard-link to an instance is deleted, the instance should
> be deleted, just like an instance from any regular class does.
class Meta(type):
all = property(lambda type: type.cache.values())
class kls(object):
__metaclass__ = Meta
cache = weakref.WeakValueDictionary()
def __new__(cls, name):
if name in kls.cache:
return kls.cache[name]
self = object.__new__(cls)
self.name = name
kls.cache[name] = self
return self
>>> x = kls(name='foo')
>>> x
<__main__.kls object at 0xb7d5dc8c>
>>> x is kls(name='foo')
True
>>> x is kls(name='bar')
False
>>> print kls.all # only one instance, 'bar' was short-lived
[<__main__.kls object at 0xb7d5dc8c>]
>>> x = 'somethingelse'
>>> print kls.all
[]
> Assuming that I have to write it on my own, what should I do? I
> tried to implement it using weakref.WeakValueDictionary and
> metaclass, but instance doesn't disappear when I think it should
> disappear. I am also wondering if it is easier to keeping
> {name:id(obj)} would be a better solution.
The problem is that, given just an ID, you have no way to get a hold
of the actual object.
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