On Fri, Mar 15, 2019 at 10:53:31PM +0000, MRAB wrote:
> There was also the suggestion of having both << and >>.
>
> Actually, now that dicts are ordered, that would provide a use-case,
> because you would then be able to choose which values were overwritten
> whilst maintaining the order of the dict on the LHS.
Is that common enough that it needs to be built-in to dict itself?
If it is uncommon, then the conventional solution is to subclass dict,
overriding the merge operator to use first-seen semantics.
The question this PEP is trying to answer is not "can we support every
use-case imaginable for a merge operator?" but "can we support the most
typical use-case?", which I believe is a version of:
new = a.copy()
new.update(b)
# do something with new
--
Steven
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