On Mon, Oct 21, 2019, 9:14 AM Rhodri James 
> The plus operation on two dictionaries feels far more natural as a vectorised merge, were it to mean anything.  E.g., I'd expect
>>>> {'a': 5, 'b': 4} + {'a': 3, 'b': 1}
> {'a': 8, 'b': 5}

That's only a natural expectation if you also expect the values in your dict to be addable (in the sense of doing something useful with a "+" operator).  It never occurs to me to make that assumption because a fair amount of the time it isn't true in my code.

I'm not arguing that we SHOULD make '+' mean recursive addition. I'm just saying that if I never read this discussion, then later read `dict1 + dict2` in code, that's what I'd expect.

I think a large percentage of the code I work with would operates insert this hypothetical meaning. Values in my ducts are usually numbers, lists, tuples, or *other dicts*. If that last had this new behavior, things would mostly work.

I don't usually write code with:

d1 = {'purchases': [apples, bananas, pears]}
d2 = {'purchases': 17}

I could, of course. But lots of things I can do raise exceptions. Like `dct[mutable_var] = val` (yes, technically "unhashable"). This one I actually wind up encountering pretty often (or with sets even more).

What is proposed in this PEP is to add a meaning for dct1+dct2 that would be well defined, but that would be DIFFERENT from the "one obvious meaning."