Rémi Lapeyre schrieb am 01.03.19 um 16:44:

Le 1 mars 2019 à 16:04:47, Stefan Behnel a écrit:

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I think the behaviour makes sense when you know how it's implemented (keys are stored separately from values).

Is a Python user expected to know the implementation details of all mappings thought?

No, it just helps _me_ in explaining the behaviour to myself. Feel free to look it up in the documentation if you prefer.

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I would have been less surprised if the keys had also been reordered, but well, this is how it is now in Py3.6+, so this is how it's going to work also for the operator.

No *additional* surprises here. ;)

There is never any surprises left once all details have been carefully worked out but having `+` for mappings make it looks like an easy operation whose meaning is non ambiguous and obvious.

I’m still not convinced that it the meaning is obvious, and gave an example in my other message where I think it could be ambiguous.

What I meant was that it's obvious in the sense that it is no new behaviour at all. It just provides an operator for behaviour that is already there. We are not discussing the current behaviour here. That ship has long sailed with the release of Python 3.6 beta 1 back in September 2016. The proposal that is being discussed here is the new operator. Stefan