[Python-ideas] Dict joining using + and +=

[INADA Naoki]

On Fri, Mar 1, 2019 at 9:47 PM Chris Angelico <rosuav at gmail.com> wrote:
>
> On Fri, Mar 1, 2019 at 11:00 PM INADA Naoki <songofacandy at gmail.com> 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.
> >
> > In case of dict + dict, it not only sum.  There may be loss value.
> >
> >    {"a":1} + {"a":2} = ?
> >
> > In case of a.update(b), it's clear that b wins.
> > In case of a + b, "which wins" or "exception raised on duplicated key?" is unclear to me.
>
> Picking semantics can be done as part of the PEP discussion, and
> needn't be a reason for rejecting the proposal before it's even made.

Yes.  I say just no semantics seems clear to me.  I don't discuss
which one is best.
And I say only I dislike it.  It must be free to express like or dislike, no?

> We have at least one other precedent to consider:
>
> >>> {1} | {1.0}
> {1}
> >>> {1.0} | {1}
> {1.0}

It is just because of behavior of int and float.  It is not caused by
set behavior.
Set keeps "no loss" semantics when view of equality.

>>> {1} <= ({1} | {1.0})
True
>>> {1.0} <= ({1} | {1.0})
True

So dict + dict is totally different than set | set.
dict + dict has los at equality level.

-- 
INADA Naoki  <songofacandy at gmail.com>