[Python-Dev] performance of {} versus dict()

Mark Adam dreamingforward at gmail.com
Wed Nov 14 19:54:32 CET 2012

On Wed, Nov 14, 2012 at 12:12 PM, Xavier Morel <catch-all at masklinn.net> wrote:
> On 2012-11-14, at 18:10 , Mark Adam wrote:
>> Try the canonical {'x':1}.  Only dict allows the special
>> initialization above.  Other collections require an iterable.
> Other collections don't have a choice, because it would often be
> ambiguous. Dicts do not have that issue.


>>  I'm guessing
>> **kwargs initialization was only used because it is so simple to
>> implement, but that's not necessarily a heuristic for good language design.
> In this case it very much is, it permits easily merging two dicts in a
> single expression or cloning-with-replacement. It also mirrors the
> signature of dict.update which I think is a Good Thing.

Merging of two dicts is done with dict.update.   How do you do it on
initialization?  This doesn't make sense.


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