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[Python-Dev] Add a "transformdict" to collections

Paul Moore p.f.moore at gmail.com
Tue Sep 10 21:08:56 CEST 2013 
On 10 September 2013 19:31, Antoine Pitrou <solipsis at pitrou.net> wrote:
>> I think it would be a flaw to have this detail implementation-defined.
>> This would be like saying that it is implementation-defined which
>> of A,B,C is returned from "A and B and C" if all are true.
>
> Ok, it seems everyone (except me :-)) agrees that it should return the
> first key value, so that's how it will be.

If you retain the first key value, it's easy enough for the
application to implement "retain the last" semantics:

try:
    del d[k]
finally:
    d[k] = v

If you provide "retain the last", I can't see any obvious way of
implementing "retain the first" in application code without in effect
reimplementing the class.

Paul
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