On Mon, Mar 4, 2019, 11:45 AM Steven D'Aprano <st...@pearwood.info> wrote:
> > Like other folks in the thread, I also want to merge dicts three times > per > > year. > > I'm impressed that you have counted it with that level of accuracy. Is it > on the same three days each year, or do they move about? *wink* > To be respectful, I always merge dicts on Eid al-Fitr, Diwali, and Lent. I was speaking approximate since those do not appears line up with the same Gregorian year. > And every one of those times, itertools.ChainMap is the right way to do > that non-destructively, and without copying. > > Can you elaborate on why ChainMap is the right way to merge multiple dicts > into a single, new dict? > Zero-copy. > ChainMap also seems to implement the opposite behaviour to that usually > desired: first value seen wins, instead of last: > True, the semantics are different, but equivalent, to the proposed dict addition. I put the key I want to "win" first rather than last. If you know ahead of time which order you want, you can simply reverse it: > This seems nonsensical. If I write, at some future time, 'dict1+dict2+dict3' I need exactly as much to know "ahead of time" which keys I intend to win.
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