[Python-Dev] Ordering keyword dicts (original) (raw)

Barry Warsaw barry at python.org
Mon May 20 15:39:45 CEST 2013

On May 20, 2013, at 02:30 PM, Armin Rigo wrote:

Just checking: in view of Raymond's proposal, is there a good reason against having all dicts be systematically ordered? It would definitely improve the debugging experience, by making multiple runs of the same program more like each other, instead of depending on the random address-based ordering. (Performance-wise, I guess it might be a little bit slower or faster depending on cache issues and so on, but the emphasis I'd put is on the "little bit".)

I'm ambivalent on the proposal -- I could get behind it if it was demonstrably not a performance hit (I'm already fighting enough "Python is too slow" battles).

However, if such a change were made, I think it must be adopted as a change to the language specification. Meaning, if dicts (or even just keyword arguments) are to be ordered, it can't be as a side-effect of the implementation. We've had a lot of churn getting code and tests to the point where most libraries have adjusted to the undefined order of dictionary iteration. I don't want to go back to the situation where lots of implicit ordering assumptions caused broken code when run in one implementation or another.

Or in other words, if dicts are to be ordered, let's make it an explicit language feature that we can measure compliance against.

-Barry

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