Thanks very much for the survey (which actually surprised me somewhat). Regarding the suggested update for the PEP, I'll make a PR to change that -- I agree it's worth saying it.
On Sat, Nov 21, 2020 at 5:00 PM David Foster <davidf...@gmail.com> wrote: > On 11/19/20 10:08 PM, David Foster wrote: > > I've completed my survey of how other languages use pattern matching to > > match Mapping-like and dict-like types, especially focusing on whether > > they ignore (𝔸) or disallow (𝔹) extra keys by default. [...] > > To close the loop on this thread: > > * Based on (1) the explanation from PEP 622 and Guido RE that "mappings > [...] have natural structural sub-typing behavior, i.e., passing a > dictionary with extra keys somewhere will likely just work" and (2) the > survey results, I'm now personally fine (+0) with keys being ignored by > default when matching against mappings. > > > * I do think it might be illustrative to copy the following explanatory > sentences from the "Mapping Patterns" section of the older PEP 622 to > the same section of PEP 635 (Structural Pattern Matching: Motivation and > Rationale): > > > Extra keys in the subject are ignored even if **rest is not present. > This is different from sequence pattern, where extra items will cause a > match to fail. But mappings are actually different from sequences: they > have natural structural sub-typing behavior, i.e., passing a dictionary > with extra keys somewhere will likely just work. > > Specifically the above might replace the following sentence in PEP 635, > which doesn't really give a rationale: > > > Moreover, the mapping pattern does not check for the presence of > additional keys. > > > * I still have an interest in strictly matching dictionaries that are > destined to become TypedDicts, but I can take that conversation to a > different thread. > > -- > David Foster | Seattle, WA, USA > Contributor to TypedDict support for mypy > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/K5BUKMOCIBUQIITBUQNX6KEHOB4WB5BC/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
_______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/4VCATZRVSNIZM4YUJJHCIDE6ARKO6LE6/ Code of Conduct: http://python.org/psf/codeofconduct/
