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

MRAB python at mrabarnett.plus.com
Tue Apr 30 01:22:49 CEST 2013

On 29/04/2013 21:00, Steven D'Aprano wrote:

On 30/04/13 05:02, MRAB wrote:

Why is that backwards? MoreColor is a subclass of Color, so instances of MoreColor are instances of Color, but instances of Color are not instances of MoreColor. That's normal behaviour for subclasses. (All cats are mammals, but not all mammals are cats.)

Let's say that Color is red, green, or blue. Let's also say that MoreColor is superset of Color, in other words, any of Color, plus cyan, magenta, or yellow. Red is a Color and a MoreColor (member of Color and MoreColor). Yellow is a MoreColor, but not a Color (member of MoreColor but not Color). That's the opposite of the rules of inheritance. Membership != inheritance, you are conflating two independent concepts. I would expect that for membership testing, you should say "value in MoreColor", not isinstance(value, MoreColor). I do know the difference, but it's not helpful that you're creating the enum with a "class" statement!

flufl.enum has been in use for Mailman for many years, and I would like to hear Barry's opinion on this.

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