[Python-Dev] Enumeration items: type(EnumClass.item) is EnumClass ? (original) (raw)

Guido van Rossum guido at python.org
Mon Apr 29 17:39:41 CEST 2013

Indeed, the "type(Color.red) is Color" claim was meant for the situation where red is defined directly in Color, and I used type() instead of isinstance() because Barry was proposing to overload isinstance() to make this true without equating the classes. But for the subclass case, I want MoreColor.red is Color.red and isinstance(MoreColor.red, Color), but not isinstance(Color.red, MoreColor). If you can't live with that, don't subclass enums.

On Mon, Apr 29, 2013 at 6:32 AM, Ethan Furman <ethan at stoneleaf.us> wrote:

[creating new thread]

On 04/29/2013 01:30 AM, Steven D'Aprano wrote:

On Sun, Apr 28, 2013 at 11:50:16PM -0700, Ethan Furman wrote:

In other words, currently:

class Color(Enum): red = 1 green = 2 blue = 3 class MoreColor(Color): cyan = 4 magenta = 5 yellow = 6 black = 7 MoreColor.red is Color.red # True Correct.

But as soon as: type(Color.red) is Color # True type(MoreColor.red) is MoreColor # True I don't believe this is correct. As I understand it, the proposal is the weaker guarantee: isinstance(Color.red, Color) # True, possibly using instancecheck Words from Guido: On 04/23/2013 08:11 AM, Guido van Rossum wrote: I gotta say, I'm with Antoine here. It's pretty natural (also coming from other languages) to assume that the class used to define the enums is also the type of the enum values. Certainly this is how it works in Java and C++, and I would say it's the same in Pascal and probably most other languages. On 04/25/2013 02:54 PM, Guido van Rossum wrote: I don't know what's going on, but it feels like we had this same discussion a week ago, and I still disagree. Disregarding, the C[i] notation, I feel quite strongly that in the following example: class Color(Enum): red = 1 white = 2 blue = 3 orange = 4 the values Color.red etc. should be instances of Color. This is how things work in all other languages that I am aware of that let you define enums. On 04/25/2013 03:19 PM, Guido van Rossum wrote: I suppose you were going to propose to use isinstance() overloading, but I honestly think that Color.red.class should be the same object as Color. On 04/25/2013 03:37 PM, Guido van Rossum wrote: TBH I had a hard time getting over the fact that even though the class said "a = 1", C.a is not the integer 1. But I did get over it. Hopefully you can get over this weirdness. [and from the summary thread] On 04/28/2013 01:02 PM, Guido van Rossum wrote: On Sun, Apr 28, 2013 at 12:32 PM, Ethan Furman wrote:

- should enum items be of the type of the Enum class? (i.e. type(SPRING) is Seasons) IMO Yes.

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-- --Guido van Rossum (python.org/~guido)

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