On Thu, Mar 7, 2019 at 12:59 AM Michael Lee <michael.lee.0...@gmail.com> wrote:
> If your instinct is to assume "+" means "concatenation", then it would be
> natural to assume that {"a": 1, "b": 2} + {"c": 3, "b": 4} would be identical
> to {"a": 1, "b": 2, "c": 3, "b": 4} -- literally concat the key-value pairs
> into a new dict.
>
> But of course, you can't have duplicate keys in Python. So, you would either
> recall or look up how duplicate keys are handled when constructing a dict and
> learn that the rule is that the right-most key wins. So the natural
> conclusion is that "+" would follow this existing rule -- and you end up with
> exactly the behavior described in the PEP.
>
Which, by the way, is also consistent with assignment:
d = {}; d["a"] = 1; d["b"] = 2; d["c"] = 3; d["b"] = 4
Rightmost one wins. It's the most logical behaviour.
ChrisA
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