[Python-Dev] PEP 435 -- Adding an Enum type to the Python standard library (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Sun Apr 21 07:33:52 CEST 2013

On Sun, Apr 21, 2013 at 11:29 AM, Steven D'Aprano <steve at pearwood.info> wrote:

I would argue that it is the responsibility of enums to start with the least restrictions as is reasonable, and leave additional restrictions up to subclasses, rather than the other way around. (I'll just quietly mention the Liskov Substitution Principle here...) If some people need enums to have unique values, then enforcing that should be their responsibility, and not forced on all users whether they need that restriction or not.

If there is enough demand for that, then perhaps the enum module could provide a standard mechanism for enforcing unique values, via a flag, or a subclass, say.

The PEP is fine, as it already allows duplicate names without encouraging them:

class Insect(Enum):
    wasp = 1  # Preferred. Use this in new code.
    bee = 2
    ant = 3
# Backwards compatibility aliases
Insect.wsap = Insect.wasp

If you have a lot of such aliases:

aliases = { "wasp": ["wsap"], ... } for attr, names in aliases.items(): for name in names: setattr(Insect, name, getattr(Insect, attr))

A more concise syntax for handling duplicates may prove desirable at some point in the future, but this is a case where encouraging correctness by default is a good idea.

Cheers, Nick.

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

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