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

[George Castillo]

>
> 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?

~ George


On Wed, Feb 27, 2019 at 10:06 AM Guido van Rossum <guido at python.org> wrote:

> On Wed, Feb 27, 2019 at 8:50 AM Rhodri James <rhodri at kynesim.co.uk> wrote:
>
>> On 27/02/2019 16:25, João Matos wrote:
>> > I would like to propose that instead of using this (applies to Py3.5
>> and upwards)
>> > dict_a = {**dict_a, **dict_b}
>> >
>> > we could use
>> > dict_a = dict_a + dict_b
>> >
>> > or even better
>> > dict_a += dict_b
>>
>> While I don't object to the idea of concatenating dictionaries, I feel
>> obliged to point out that this last is currently spelled
>> dict_a.update(dict_b)
>>
>
> This is likely to be controversial. But I like the idea. After all, we
> have `list.extend(x)` ~~ `list += x`. 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`.
>
> --
> --Guido van Rossum (python.org/~guido)
> _______________________________________________
> Python-ideas mailing list
> Python-ideas at python.org
> https://mail.python.org/mailman/listinfo/python-ideas
> Code of Conduct: http://python.org/psf/codeofconduct/
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20190227/d189f322/attachment.html>