Interning own classes like strings for speed and size?

[Steven D'Aprano]

On Mon, 27 Dec 2010 12:05:10 +0100, Ulrich Eckhardt wrote:

> What I'm now considering is to only allow a single instance of these
> objects for each set of values, similar to interned strings. What I
> would gain is that I could safely compare objects for identity instead
> of equality. What I'm not yet sure is how much overhead that would give
> me and/or how to keep it low. The idea is to store each instance in a
> set and after creating a new object I would first look up an equal
> object in the global set and return that instead, otherwise add the new
> one.

Try this technique:

>>> class InternedTuple(tuple):
...     _cache = {}
...     def __new__(cls, *args):
...             t = super().__new__(cls, *args)
...             return cls._cache.setdefault(t, t)
... 
>>> 
>>> 
>>> t1 = InternedTuple((1.0, 2.0))
>>> t2 = InternedTuple((0.0, 0.0))
>>> t3 = InternedTuple((1.0, 2.0))
>>> 
>>> t1 is t2
False
>>> t1 is t3
True
>>> t1 == t2
False
>>> t1 == t3
True



-- 
Steven