On Fri, Mar 1, 2019 at 10:10 PM Steven D'Aprano <st...@pearwood.info> wrote:
>
> On Fri, Mar 01, 2019 at 08:59:45PM +0900, INADA Naoki wrote:
> > I dislike adding more operator overload to builtin types.
> >
> > str is not commutative, but it satisfies a in (a+b), and b in (a+b).
> > There are no loss.
>
> Is this an invariant you expect to apply for other classes that support
> the addition operator?
>
> 5 in (5 + 6)
I meant more high level semantics: "no loss". Not only "in".
So my example about set used "<=" operator.
5 + 6 is sum of 5 and 6.
>
> [1, 2, 3] in ([1, 2, 3] + [4, 5, 6])
>
Both of [1,2,3] and [4,5,6] are not lost in result.
>
> Since it doesn't apply for int, float, complex, list or tuple, why do
> you think it must apply to dicts?
>
You misunderstood my "no loss" expectation.
>
> > In case of dict + dict, it not only sum. There may be loss value.
>
> Yes? Why is that a problem?
>
It's enough reason to I dislike.
>
> > {"a":1} + {"a":2} = ?
>
> Would you like to argue that Counter.__add__ is a mistake for the same
> reason?
>
In Counter's case, it's clear. In case of dict, it's unclear.
> Counter(('a', 1)) + Counter(('a', 2)) = ?
>
>
> For the record, what I expected the above to do turned out to be
> *completely wrong* when I tried it. I expected Counter({'a': 3}) but the
> actual results are Counter({'a': 2, 1: 1, 2: 1}).
It just because you misunderstood Counter's initializer argument.
It's not relating to how overload + or | operator.
>
> Every operation is going to be mysterious if you have never
> learned what it does:
>
> from array import array
> a = array('i', [1, 2, 3])
> b = array('i', [10, 20, 30])
> a + b = ?
>
> Without trying it or reading the docs, should that be an
> error, or concatenation, or element-wise addition?
>
I never say every operator must be expected by everyone.
Don't straw man.
--
INADA Naoki <songofaca...@gmail.com>
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