__lt__ slowing the "in" operator even if not called

[Maric Michaud]

Le Jeudi 15 Juin 2006 14:14, Emanuele Aina a écrit :
> > Every classes that define the __eq__ operator will find quickly the
> > elements if they are at the beginning of the list.
> > If they are at the end, the in oprerator is slower in these classes
> > because of the overhead of function calls (in StateLt there is also an
> > overhead due to
>
>                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> > internal lookup, IMO).
>
>   ^^^^^^^^^^^^^^^
>
> Yes, that was my question! :)
>
> But I hoped in a more exaustive answer: why python has to do this
> lookup when the __lt__ method is not involved at all?

Ah, ok sorry, got your point, I didn't notice it in first time.
There is effectively an overhead when the class defines at less one of __lt__, 
__gt__, __neq__ ... special attributes (comparison attributes), it seems in 
my example that this overhead is a ratio of 1,5x.

It is related to comparison, as the following code show :


import timing

class State(object):
    def __init__(self, value):
        self.v = value

class StateFoo(State) :
    def foo(self) : pass

class StateNew(State) :
    def __nonzero__(self) : return None

class StateGT(State) :
    def __gt__(self) : return None

class StateGTLT(StateGT) :
    def __lt__(self) : return None

def test(cls) :
    print cls
    inst = cls(5)
    timing.start()
    for i in xrange(10**6) : i == inst
    timing.finish()
    print timing.milli()

test(State)
test(StateFoo)
test(StateNew)
test(StateGT)
test(StateGTLT)

for which ouput is : 

<class '__main__.State'>
589
<class '__main__.StateFoo'>
596
<class '__main__.StateNew'>
615
<class '__main__.StateGT'>
815
<class '__main__.StateGTLT'>
836

Can't say more about what in the internals of python produce this non 
negligeable overhead, but looking at the source code of builtin comparison 
(for new style classes as it seems we have not this overhead with old style 
classes) should be the fist step...

-- 
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Maric Michaud
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