[Python-ideas] Adding "+" and "+=" operators to dict

[Chris Barker]

On Tue, Feb 17, 2015 at 2:22 PM, C Anthony Risinger <anthony at xtfx.me> wrote:

> The premise taken here is that dicts ARE sets that simply happen to have
> values associated with them... hence all operations are against keys ONLY.
> The fact that values tag along is irrelevant.
>

but dicts DO have values, and that's their entire reason for existence --
if the values were irrelevant, you'd use a set....

And because values are important -- there is no such thing as "works the
same as a set". For instance:

# union (first key winning here... IIRC this is how sets actually work)
> >>> d1 | d2
> {'a': 1, 'b': 2, 'c': 3, 'd': 5, 'e': 6}
>

The fact that sets may, under the hood, keep the first key is an
implementation detail  -- by definition the first and second duplicate keys
are the same. So there is no guidance here whatsoever as to what to do with
with unioning dicts.

Oh, except .update() provides a precedent that has proven to be useful.
Keeping the second value sure feels more natural to me.

Oh, and I'd still prefer + I don't think most users think of merging two
dicts together as a boolean logical operation....

All of the operations support arbitrary iterables as the RHS! This is NICE.
>

not so sure about that -- again, dicts have values, that's why we use them.
Maybe defaultdict could work this way, though.

-Chris


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