marduk wrote:
> On Wed, 2005-10-05 at 12:56 -0400, Jonathan LaCour wrote:
>> > class Spam(object):
>> > cache = {}
>> > def __new__(cls, x):
>> > if cls.cache.has_key(x):
>> > return cls.cache[x]
>> > def __init__(self, x):
>> > self.x = x
>> > self.cache[x] = self
>> >
>> > a = Spam('foo')
>> > b = Spam('foo')
>> >
>> > Well, in this case a and b are identical... to None! I assume this is
>> > because the test in __new__ fails so it returns None, I need to then
>> > create a new Spam.. but how do I do that without calling __new__
>> > again?
>> > I can't call __init__ because there's no self...
>> >
>> >
>>
>> Oops, you forgot to return object.__new__(cls, x) in the case the
>> object isn't in the cache. That should fix it.
>
> Okay, one more question... say I then
>
> c = Spam('bar')
> del a
> del b
>
> I've removed all references to the object, except for the cache. Do I
> have to implement my own garbage collecting is or there some "magical"
> way of doing this within Python? I pretty much want to get rid of the
> cache as soon as there are no other references (other than the cache).
Use a weakref.WeakValueDictionary as the cache instead of a normal dict.
Peter
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