+1 On Mon, Mar 15, 2021 at 12:48 PM Ethan Furman <et...@stoneleaf.us> wrote:
> On 3/15/21 11:27 AM, Guido van Rossum wrote: > > On Mon, Mar 15, 2021 at 10:53 AM Ethan Furman wrote: > > >> Part of the reason is that there are really two ways to identify an > >> enum -- by name, and by value -- which should `__contains__` work with? > > > > The two sets don't overlap, so we could allow both. (Funny > > interpretations of `__contains__` are not unusual, e.g. > > substring checks are spelled 'abc' in 'fooabcbar'.) > > They could overlap if the Enum is a `str`-subclass -- although having the > name of one member match the value of a different member seems odd. > > >> I think I like your constructor change idea, with a small twist: > >> > >> Color(value=<sentinel>, name=<sentinel>, default=<sentinal>) > >> > >> This would make it possible to search for an enum by value or by name, > >> and also specify a default return value (raising an exception if the > >> default is not set and a member cannot be found). > > > > > > So specifically this would allow (hope my shorthand is clear): > > ``` > > Color['RED'] --> Color.RED or raises > > Color(1) -> Color.RED or raises > > Color(1, default=None) -> Color.RED or None > > Color(name='RED', default=None) -> Color.RED or None > > ``` > > This seems superficially reasonable. I'm not sure what > > Color(value=1, name='RED') would do -- insist that both value and > > name match? Would that have a use case? > > I would enforce that both match, or raise. Also not sure what the > use-case would be. > > > My remaining concern is that it's fairly verbose -- assuming we don't > > really need the name argument, it would be attractive if we could > > write Color(1, None) instead of Color(1, default=None). > > > > Note that instead of Color(name='RED') we can already write this: > > ``` > > getattr(Color, 'RED') -> Color.RED or raises > > getattr(Color, 'RED', None) -> Color.RED or None > > Very good points. > > Everything considered, I think I like allowing `__contains__` to verify > both names and values, adding `default=<sentinel>` to the constructor for > the value-based "gimme an Enum or None" case, and recommending `getattr` > for the name-based "gimme an Enum or None" case. > > -- > ~Ethan~ > _______________________________________________ > 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/UQBSDZQJWBKMOVSUES7HEDJTYR76Y5N2/ > 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/>
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