[Python-Dev] PEP 455: TransformDict (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Wed Oct 9 23:34:11 CEST 2013

On 9 Oct 2013 01:07, "Antoine Pitrou" <solipsis at pitrou.net> wrote:

Le Tue, 8 Oct 2013 22:49:28 +1000, Nick Coghlan <ncoghlan at gmail.com> a écrit : > > Well, you could ask the same question about OrderedDict, > > defaultdict or Weak*Dictionary since neither of them use > > composition :-) > > We did ask the same question about those (except the Weak* variants, > simply due to age). > > Each time, the point that each new dict variant would be used to > justify yet more variants was a cause for concern. Could you explain? I don't understand.

Just that the comment I replied to is getting very close to the argument "we have so many non-composable mapping variants already, what's the harm in adding one more?". I believe potentially enabling that argument in the future was cited as a downside for all of defaultdict, OrderedDict and Counter.

> "Composition doesn't work with some mappings" isn't an adequate > answer to the criticism that a composition based design could work > with more mappings than just the builtin dict.

Fair enough. Regards Antoine.

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