[Python-ideas] dict(default=int)

[Neil Girdhar]

On Mon, May 29, 2017 at 5:06 PM Matt Gilson <matt at getpattern.com> wrote:

> On Mon, May 29, 2017 at 11:59 AM, Neil Girdhar <mistersheik at gmail.com>
> wrote:
>
>> A long time ago, I proposed that the dict variants (sorteddict,
>> defaultdict, weakkeydict, etc.) be made more discoverable by having them
>> specified as keyword arguments and I got the same feedback that the poster
>> here is getting.  Now, instead of moving these classes into dict, why not
>> have a factory like
>>
>> dict.factory(values=None, *, ordered=True, sorted=False,
>> has_default=False, weak_keys=False, weak_values=False, …)
>>
>
> Hmm ... I don't think that I like this.  For one, it greatly increases the
> amount of surface area that needs to be maintained in the standard
> library.  As far as I know, we don't currently have a
> OrderedWeakKeyDictionary with defaultdict behavior.  If this was to be
> added, then each of the combinations of input keyword arguments would need
> to be supported.  Many of them probably don't have very compelling
> use-cases or they might not have semantics that would be easy to agree upon
> a "preferred behavior" (Assuming that a mythological SortedDict pops into
> existence in the standard lib, what happens if you call
> `dict.factory(sorted=True, ordered=True)`?).  Of course, this sets a
> precedence that future dict subclasses need to be added to the
> `dict.factory` constructor as well which risks a very bloated signature
> (or, someone has to make the decision about which subclasses should be
> available and which should be left off ...).  This last argument can
> repurposed against providing easy access to builtin dict subclasses via
> their own methods (`dict.defaultdict(...)`).
>

You can just raise NotImplementedError for the bad combinations and the
reasonable combinations that aren't implemented yet.

>
> I don't find very cumbersome to import the dict subclasses that I need
> from the locations where they live.  I like that it forces me to be
> explicit and I think that it generally makes reading the code easier in the
> normal cases (`defaultdict(in)` vs. `dict.factory(default=int)`).  Of
> course, if someone finds this idea particularly interesting, they could
> definitely explore the idea more by creating a package on pypi that
> attempts to provide this factory function.  If it got usage, that might go
> a long way to convincing us nay-sayers that this idea has legs :-).
>

Fair enough.  The reason I had proposed it was to make the various dict
incantations more discoverable.  Also, I was using a lot of weak-key
dictionaries and it was odd to me that there was no ordered version of weak
key dictionaries, etc.

>
>
>
>
>>
>> If prefers the keyword-argument as options to the keyword-argument as
>> initializer magic, they can set:
>>
>> dict = dict.factory
>>
>> Best,
>>
>> Neil
>>
>> On Thursday, March 9, 2017 at 5:58:43 PM UTC-5, Chris Barker wrote:
>>>
>>>
>>>
>>> >If we really want to make defaultdict feel more "builtin" (and I don't
>>>> see
>>>> >any reason to do so), I'd suggest adding a factory function:
>>>> >
>>>> >dict.defaultdict(int)
>>>>
>>>
>>>
>>>> Nice.
>>>>
>>>
>>> I agree -- what about:
>>>
>>> dict.sorteddict() ??
>>>
>>> make easy access to various built-in dict variations...
>>>
>>> -CHB
>>>
>>>
>>> --
>>>
>>> Christopher Barker, Ph.D.
>>> Oceanographer
>>>
>>> Emergency Response Division
>>> NOAA/NOS/OR&R            (206) 526-6959   voice
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>>>
>>> Chris.... at noaa.gov
>>>
>>
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>>
>
>
> --
>
> Matt Gilson | Pattern
>
> Software Engineer
> getpattern.com
> <https://www.getpattern.com?utm_source=email&utm_medium=email&utm_campaign=signature-matt>
>
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