On Jul 25, 2019, at 09:46, Batuhan Taskaya <isidenti...@gmail.com> wrote:
>
> I think it looks very fine when you type {1, 2, 3} * {"a", "b", "c"} and get
> set(itertools.product({1, 2, 3}, {"a", "b", "c"})). So i am proposing set
> multiplication implementation as cartesian product.
I think it might make more sense to reopen the discussion of using @ for
cartesian product for all containers, for a few reasons.
* The * operator means repeat on lists, tuples, and strings. While there are
already some operator differences between sets and other containers, but it’s
generally the types supporting different operators (like sets having | and &,
and not having +) rather than giving different meanings to the same operators.
Plus, tuples are frequently used for small things that are conceptually sets or
set-like; this is even enshrined in APIs like str.endswith and isinstance.
* (Ordered) Cartesian product for lists, tuples, iterators, etc. makes just as
much sense even when they’re not being used as pseudo-sets, ordered sets, or
multisets, and might even be more common in code in practice (which is
presumably why there’s a function for that in the stdlib). So, why only allow
it for sets?
* Cartesian product feels more like matrix multiplication than like scalar or
elementwise multiplication or repetition, doesn’t it?
* Adding @ to the builtin containers was already raised during the @
discussion and tabled for the future. I believe this is because the NumPy
community wanted the proposal to be as minimal as possible so they could be
sure of getting it, and get it ASAP, not because anyone had or anticipated
objections beyond “is it common enough of a need to be worth it?”
I don’t think this discussion would need to include other ideas deferred at the
same time, like @ for composition on functions. (Although @ on iterators might
be worth bringing up, if only to reject it. We don’t allow + between arbitrary
iterables defaulting to chain but meaning type(lhs)(chain(…)) on some types, so
why do the equivalent with @?)
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