On Fri, Jun 29, 2018 at 2:43 PM Guido van Rossum <gu...@python.org> wrote:
> On a quick skim I see nothing particularly objectionable or controversial > in your PEP, except I'm unclear why it needs to be a class method on `dict`. > Since it constructs a basic dict, I thought it belongs best as a dict constructor like dict.fromkeys. It seemed to match other classmethods like datetime.now. > Adding something to a builtin like this is rather heavy-handed. > I included an alternate solution of a new class, collections.Grouping, which has some advantages. In addition to having less of that "heavy-handed" feel to it, the class can have a few utility methods that help handle more use cases. > Is there a really good reason why it can't be a function in `itertools`? > (I don't think that it's relevant that it doesn't return an iterator -- it > takes in an iterator.) > I considered placing it in the itertools module, but decided against because it doesn't return an iterator. I'm open to that if that's the consensus. > Also, your pure-Python implementation appears to be O(N log N) if key is > None but O(N) otherwise; and the version for key is None uses an extra > temporary array of size N. Is that intentional? > Unintentional. I've been drafting pieces of this over the last year and wasn't careful enough with proofreading. I'll fix that momentarily... > Finally, the first example under "Group and Aggregate" is described as a > dict of sets but it actually returns a dict of (sorted) lists. > Doctest complained at the set ordering, so I sorted for printing. You're not the only one to make that point, so I'll use sets for the example and ignore doctest. Thanks for reading! -- Michael PS. I just pushed an update to the GitHub repo, as per these comments. > On Fri, Jun 29, 2018 at 10:54 AM Michael Selik <m...@selik.org> wrote: > >> Hello, >> >> I've drafted a PEP for an easier way to construct groups of elements from >> a sequence. https://github.com/selik/peps/blob/master/pep-9999.rst >> >> As a teacher, I've found that grouping is one of the most awkward tasks >> for beginners to learn in Python. While this proposal requires >> understanding a key-function, in my experience that's easier to teach than >> the nuances of setdefault or defaultdict. Defaultdict requires passing a >> factory function or class, similar to a key-function. Setdefault is >> awkwardly named and requires a discussion of references and mutability. >> Those topics are important and should be covered, but I'd like to let them >> sink in gradually. Grouping often comes up as a question on the first or >> second day, especially for folks transitioning from Excel. >> >> I've tested this proposal on actual students (no students were harmed >> during experimentation) and found that the majority appreciate it. Some are >> even able to guess what it does (would do) without any priming. >> >> Thanks for your time, >> -- Michael >> >> >> >> >> >> >> On Thu, Jun 28, 2018 at 8:38 AM Michael Selik <m...@selik.org> wrote: >> >>> On Thu, Jun 28, 2018 at 8:25 AM Nicolas Rolin <nicolas.ro...@tiime.fr> >>> wrote: >>> >>>> I use list and dict comprehension a lot, and a problem I often have is >>>> to do the equivalent of a group_by operation (to use sql terminology). >>>> >>>> For example if I have a list of tuples (student, school) and I want to >>>> have the list of students by school the only option I'm left with is to >>>> write >>>> >>>> student_by_school = defaultdict(list) >>>> for student, school in student_school_list: >>>> student_by_school[school].append(student) >>>> >>> >>> Thank you for bringing this up. I've been drafting a proposal for a >>> better grouping / group-by operation for a little while. I'm not quite >>> ready to share it, as I'm still researching use cases. >>> >>> I'm +1 that this task needs improvement, but -1 on this particular >>> solution. >>> >>> _______________________________________________ >> Python-ideas mailing list >> Python-ideas@python.org >> https://mail.python.org/mailman/listinfo/python-ideas >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > > > -- > --Guido van Rossum (python.org/~guido) >
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