[Python-ideas] Where should grouping() live (was: grouping / dict of lists)

[Chris Barker]

On Tue, Jul 3, 2018 at 8:24 AM, Steven D'Aprano <steve at pearwood.info> wrote:

> On Tue, Jul 03, 2018 at 09:23:07AM -0400, David Mertz wrote:
>


> > My problem with the second idea is that *I* find it very wrong to have
> > something in itertools that does not return an iterator.  It wrecks the
> > combinatorial algebra of the module.
>

hmm -- that seems to be a pretty pedantic approach -- practicality beats
purity, after all :-)

I think we should first decide if a grouping() function is a useful
addition to the standard library (after all:  "not every two line function
needs to in the stdlib"), and f so, then we can find a home for it.

personally, I'm wondering if a "dicttools" or something module would make
sense -- I imagine there are all sorts of other handy utilities for working
with dicts that could go there. (though, yeah, we'd want to actually have a
handful of these before creating a new module :-) )

> That said, it's easy to fix... and I believe independently useful.  Just
> > make grouping() a generator function rather than a plain function.  This
> > lets us get an incremental grouping of an iterable.
>
> We already have something which lazily groups an iterable, returning
> groups as they are seen: groupby.
>
> What makes grouping() different from groupby() is that it accumulates
> ALL of the subgroups rather than just consecutive subgroupings.


well, yeah, but it wont actually get you those until you exhaust the
iterator -- so while it's different than itertools.groupby, it is different
than itertools.groupby(sorted(iterable))?

In short, this wouldn't really solve the problems that itertools.groupby
has for this sort of task -- so what's the point?

 > As for where it belongs, perhaps the collections module is the least
worst fit.

That depends some on whether we go with a simple function, in which case
collections is a pretty bad fit (but maybe still the least worse).

Personally I still like the idea of having this be special type of dict,
rather than "just a function" -- and then it's really obvious where to put
it :-)

-CHB


-- 

Christopher Barker, Ph.D.
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