Hi Nicolas, Florent and Maarten,
On 13 Sep., 09:36, "Nicolas M. Thiery" <nicolas.thi...@u-psud.fr>
wrote:
> On Tue, Sep 13, 2011 at 09:21:45AM +0200, Nicolas M. Thiery wrote:
> > What does your FastHashMetaclass do precisely?
>
> Oops, I had not read the other thread yet ...
I just created a ticket for it: #11794.
The new metaclass provides a fast hash, and thus can be useful in
applications that frequently work with, say, dictionary keys. However,
there is no free lunch. The fast hash currently comes with a
regression in accessing the other attributes:
{{{
sage: from sage.misc.fast_hash import FastHashMetaclass
sage: F = CombinatorialFreeModule(QQ, ['a','b'])
sage: h = hash(F)
sage: timeit("hash(F)")
625 loops, best of 3: 1.1 µs per loop
sage: D = dir(F)
sage: timeit('for s in D: a = getattr(F,s)', number=10000)
10000 loops, best of 3: 86.8 µs per loop
sage: F.__class__ = FastHashMetaclass(F.__class__)
sage: timeit("hash(F)")
625 loops, best of 3: 440 ns per loop
sage: timeit('for s in D: a = getattr(F,s)', number=10000)
10000 loops, best of 3: 97.3 µs per loop
}}}
To my understanding, the reason is that my metaclass adds a new layer
in the mro, and thus more steps in the mro are needed to find the old
methods. I'll try to find a better solution.
Fortunately, both the speed-up and the regression are temporary:
{{{
sage: F.__class__ = F.__class__.__base__
sage: timeit("hash(F)")
625 loops, best of 3: 1.09 µs per loop
sage: timeit('for s in D: a = getattr(F,s)', number=10000)
10000 loops, best of 3: 86.3 µs per loop
}}}
Hence, I would not suggest to use the FastHashMetaclass by default.
But perhaps it is useful in some situations.
The newly created classes seem to behave well:
{{{
sage: F.__class__ = FastHashMetaclass(F.__class__)
sage: TestSuite(F).run()
}}}
And, concerning dynamic metaclasses: Here we go.
{{{
sage: type(F)
<class
'sage.combinat.free_module.CombinatorialFreeModule_with_category_with_hash'>
sage: type(type(F))
<class 'sage.misc.fast_hash.FastHashAndDynamicClasscallMetaclass'>
sage: type(type(type(F)))
<class 'sage.structure.dynamic_class.DynamicMetaclass'>
}}}
So, the type of F has a metaclass that is a dynamic class and thus has
a metaclass as well.
Best regards,
Simon
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