[Python-Dev] a Constant addition to enum (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Wed Aug 7 07:05:26 CEST 2013

On 7 August 2013 07:36, Eli Bendersky <eliben at gmail.com> wrote:

On Tue, Aug 6, 2013 at 1:42 PM, Ethan Furman <ethan at stoneleaf.us> wrote:

A question came up on stackoverflow asking about the Planet example and the need to have the constant G defined in the method instead of at the class level: http://stackoverflow.com/q/17911188/208880 Since methods and descriptors are immune to enumeration my proposed solution created a Constant descriptor that could be used to keep class level constants at the class level. It's not complex, only about 7 lines. Should we have something like that included in the enum module? If we do include something like that, should it be constant, or should it be more like property? (The important differences from property being that class access still returns the value, not the property itself, and setting the class-level value changes the value but doesn't replace the property.) Personally, I dislike all non-simple uses of Enums. One such use is adding behavior to them. This can always be split to separate behavior from the Enum itself, and I would prefer that. We went to great lengths to ensure that things work in expected ways, but heaping additional features (even as separate decorators) is just aggravating thiings. So -1 from me. Finally, I suggest we exercise restraint in adding more capabilities to enums in 3.4; enums are a new creature for Python and it will be extremely useful to see them used in the wild for a while first. We can enhance them in 3.5, but premature enhancement is IMHO much more likely to do harm than good.

Agreed. I wouldn't be averse to taking those advanced examples out of the docs, too.

Like metaclasses, you can do crazy things with enums. "Can" doesn't mean "should", however. We've had a lot of success with metaclasses by soft-pedalling them in the standard library, so people only explore them when they really need them. I think we'd be well advised to pursue a similar path with advanced Enum tricks.

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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