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

[Guido van Rossum]

OK, you're it. Please write a PEP for this.

On Wed, Feb 27, 2019 at 3:53 PM Steven D'Aprano <steve at pearwood.info> wrote:

> On Wed, Feb 27, 2019 at 10:34:43AM -0700, George Castillo wrote:
> > >
> > > The key conundrum that needs to be solved is what to do for `d1 + d2`
> when
> > > there are overlapping keys. I propose to make d2 win in this case,
> which is
> > > what happens in `d1.update(d2)` anyways. If you want it the other way,
> > > simply write `d2 + d1`.
> >
> >
> > This would mean that addition, at least in this particular instance, is
> not
> > a commutative operation.  Are there other places in Python where this is
> > the case?
>
> Strings, bytes, lists, tuples.
>
> In this case, I wouldn't call it dict addition, I would call it a union
> operator. That suggests that maybe we match sets and use | for union.
>
> That also suggests d1 & d2 for the intersection between two dicts, but
> which value should win?
>
> More useful than intersection is, I think, dict subtraction: d1 - d2
> being a new dict with the keys/values from d1 which aren't in d2.
>
>
>
> --
> Steven
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-- 
--Guido van Rossum (python.org/~guido)
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