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

[Brandt Bucher]

Here is a working implementation of dictionary addition, for consideration with the PEP:

https://bugs.python.org/issue36144

Brandt

> On Feb 27, 2019, at 16:07, Guido van Rossum <guido at python.org> wrote:
> 
> 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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