On Tue, 28 Dec 2010 13:42:39 +0100, Ulrich Eckhardt wrote:
> Steven D'Aprano wrote:
>>>>> class InternedTuple(tuple):
>> ... _cache = {}
>> ... def __new__(cls, *args):
>> ... t = super().__new__(cls, *args)
>> ... return cls._cache.setdefault(t, t)
>
> That looks good. The only thing that first bothered me is that it
> creates an object and then possibly discards it again. However, there is
> no way around that, since at least the key to the dict must be created
> for lookup. Since key and value are the same here, this is even for
> free.
>
> What I also found was that with the above, I can't provide __eq__ and
> __ne__ that just check for identity. If I do, the lookup in setdefault()
> will never find an existing tuple and I will never save memory for a
> single object.
If all you want is to save memory, you don't need to change the __eq__
method. But if you still want to, try this:
# Untested
class InternedTuple(tuple):
_cache = {}
def __new__(cls, *args):
t = super().__new__(cls, *args)
return cls._cache.setdefault(args, t)
def __eq__(self, other):
return self is other
def __ne__(self, other):
return self is not other
--
Steven
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