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`. Adding something to a builtin like this is rather heavy-handed. 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.)
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? Finally, the first example under "Group and Aggregate" is described as a dict of sets but it actually returns a dict of (sorted) lists. 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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