Interning own classes like strings for speed and size?

[Steven D'Aprano]

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