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

[Alexander Heger]

>> I had started a previous thread on this, asking why there was no
>> addition defined for dictionaries, along the line of what Peter argued
>> a novice would naively expect.
> [...]
> I don't think that "novices would naively expect this" is correct, and
> even if it were, I don't think the language should be designed around
> what novices naively expect.

well, I had at least hoped this to work while not being a novice.
Because it would be nice.

> As far as I was, and still am, concerned, & is the obvious and most
> natural operator for concatenation. [1, 2]+[3, 4] should return [4, 6],
> and sum(bunch of lists) should be a meaningless operation, like
> sum(bunch of HTTP servers). Or sum(bunch of dicts).

This only works if the items *can* be added.  Dics should not make
such an assumption. & is not a more natural operator, because, why
would you then not just expect that [1, 2] & [3, 4] returns [1 & 2, 3
& 4] == [0 , 0] ?  the same would be true for any operator you pick.

You just define that combination of dics, + or whatever operator is
used, combines dicts using the update operation.  This is how dicts
behave.

> No, that's not the argument. The argument is not that "we used the +
> operator to merge two dicts, so merging should + the values". The
> argument is that in the event of a duplicate key, adding the values
> is sometimes a common and useful thing to do.

... and sometimes it is not; in general it will fail.  Replacing always works.

-Alexander