[Python-Dev] __contains__ hook

[M.-A. Lemburg]

Guido van Rossum wrote:
> 
> > Shouldn't 'in' be a slot of the sequence methods ? I'd suggest
> > creating a new tp_flag bit and then extending tp_as_sequence
> > with:
> >
> >       binaryfunc sq_contains;
> >
> > plus of course add an abstract function to abstract.c:
> >
> >       PySequence_Contain(PyObject *container, PyObject *element)
> 
> That function already exists, spelled "PySequence_Contains" (currently
> it does the C equivalent of
> 
>    for i in container:
>        if element == i: return 1
>    return 0

Hmm, I must have overseen that one... the above only works
for sequences, while 'in'ness only need an unordered set
to work. Perhaps we do need an abstraction for unordered
object containers after all, just like Moshe suggested.

I don't think it's top-priority, though...

> I'm not entirely sure whether the 'contains' slot should be part of
> the as_sequence struct, but I suppose it makes sense historically.
> (The as_number, as_sequece, as_mapping structs don't make sense at all
> in the grand scheme of things, but we're stuck with them for the time
> being.)

Doens't really matter where we put it -- the type object is
a mess already ;-)

-- 
Marc-Andre Lemburg
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