Tuesday 12 April 2005 17:00 pm Michele Simionato wrote:
> I did not put memoize on __new__. I put it on the metaclass __call__.
> Here is my memoize:
>
> def memoize(func):
> memoize_dic = {}
> def wrapped_func(*args):
> if args in memoize_dic:
> return memoize_dic[args]
> else:
> result = func(*args)
> memoize_dic[args] = result
> return result
> wrapped_func.__name__ = func.__name__
> wrapped_func.__doc__ = func.__doc__
> wrapped_func.__dict__ = func.__dict__
> return wrapped_func
>
> class Memoize(type): # Singleton is a special case of Memoize
> @memoize
> def __call__(cls, *args):
> return super(Memoize, cls).__call__(*args)
I tried it out and found the following "inconsistency":
>>> class Foobar(object):
... __metaclass__ = Memoize
... def __init__(self, *args): pass
...
>>> Foobar(1)
<__main__.Foobar object at 0x4006f7ec>
>>> Foobar(2)
<__main__.Foobar object at 0x4006f7cc>
>>> Foobar(3)
<__main__.Foobar object at 0x4006f82c>
Unless I'm using it incorrectly (I haven't done much metaclass programming
yet) this is the same problem was with using @memoize on __new__ and
__init__.
Talking so much about singletons I'm not even sure what the definition on
calling a singleton with different constructor parameter values is.
Anyways, a fix for that could be:
class SingletonFactory(type):
single = {}
def __call__(cls, *args):
if (cls not in SingletonFactory.single):
SingletonFactory.single[cls] = super(SingletonFactory,
cls).__call__(*args)
return SingletonFactory.single[cls]
i.e. not caching the parameter values or types.
Uwe
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