[Python-Dev] Add __reversed__ methods for dict

[Victor Stinner]

INADA Naoki asked Rémi Lapeyre in https://bugs.python.org/issue33462
to start a discussion on python-dev.

Victor

2018-05-25 17:48 GMT+02:00 Guido van Rossum <guido at python.org>:
> (Also this probably belongs in python-ideas, unless there's already a
> bugs.python.org issue for it -- but you didn't mention that so I assume it's
> just an idea? How did you reach the line count estimates?)
>
> On Fri, May 25, 2018 at 8:46 AM, Guido van Rossum <guido at python.org> wrote:
>>
>> Please go find some real world code that would benefit from this. Don't
>> make up examples, just show some code in a repository (public if possible,
>> but private is okay, as long as you can quote small amounts of code from it)
>> where te existence of reverse iteration over a dict would have been helpful.
>>
>> On Thu, May 24, 2018 at 5:55 AM, Rémi Lapeyre <remi.lapeyre at vint.fr>
>> wrote:
>>>
>>>
>>> Hi,
>>>
>>> since dict keys are sorted by their insertion order since Python 3.6 and
>>> that
>>> it’s part of Python specs since 3.7 a proposal has been made in bpo-33462
>>> to
>>> add the __reversed__ method to dict and dict views.
>>>
>>> Concerns have been raised in the comments that this feature may add too
>>> much
>>> bloat in the core interpreter and be harmful for other Python
>>> implementations.
>>>
>>> Given the different issues this change creates, I see three
>>> possibilities:
>>>
>>> 1. Accept the proposal has it is for dict and dict views, this would add
>>> about
>>> 300 lines and three new types in dictobject.c
>>>
>>> 2. Accept the proposal only for dict, this would add about 80 lines and
>>> one
>>> new type in dictobject.c while still being useful for some use cases
>>>
>>> 3. Drop the proposal as the whole, while having some use,
>>> reversed(dict(a=1, b=2))
>>> may not be very common and could be done using OrderedDict instead.
>>>
>>> What’s your stance on the issue ?
>>>
>>> Best regards,
>>> Rémi Lapeyre
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>>
>>
>>
>>
>> --
>> --Guido van Rossum (python.org/~guido)
>
>
>
>
> --
> --Guido van Rossum (python.org/~guido)
>
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