[Python-Dev] Enum Eccentricities

[Guido van Rossum]

On Mon, Sep 23, 2013 at 8:17 AM, Zero Piraeus <z at etiol.net> wrote:

> On Mon, Sep 23, 2013 at 09:45:46AM -0400, Chris Lambacher wrote:
> > [...] The exact use case is in Django templates where a value comes
> > from the database. If you want to compare you either have to use
> > __class__ which I would say is a code smell, or you have
> > to provide the Enum class.
>
> I'm having a hard time seeing why the latter is problematic, I must
> admit (certainly no more so than the "Alice in Wonderland" side effects
> previously described).
>
> > [...] An example of how this will be used in practice is:
> >
> >     {% if object.state == object.state.completed %}
> >       some html
> >     {% endif %}
>
> The names used slightly obscure the weirdness of it, but what you're
> really saying there is:
>
>     if my_state == my_state.another_state
>
> ... which feels more like a code smell to me than
>
>      {% if object.state == State.completed %}
>        some html
>      {% endif %}
>
> That's quite intelligible, and doesn't require anyone to know that an
> Enum member's siblings can, in your proposal, be accessed directly via
> dot notation (an unintuitive state of affairs, to me at least).
>

Right. The OP is just concerned that (because these are Django templates)
he will have to pass in the 'State' class as a separate template parameter
for this to work. But to me that's a problem with Django, and not something
for which the Enum type should bend over backwards to cover up for. Given
that it's a Djano weakness, IMO the __class__ solution is reasonable
enough, although in theory it would allow having object.state be something
of the wrong class that happens to have a 'completed' attribute -- that
would be a bug of a different color, though. :-)

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