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~