[Python-ideas] proper naming of Enum members

[Guido van Rossum]

Honestly my own preference would be to use UPPER_CASE, emphasizing the
const-ness. CapWords is really only used for classes, which are
entirely different beasts. And lower_case is for methods and
variables. I think it's useful to emphasize that an enum is neither.

On Mon, Jul 18, 2016 at 8:17 AM, Ethan Furman <ethan at stoneleaf.us> wrote:
> There are currently a few locations in the stdlib, such as http and socket,
> that are now using
> Enums to replace constants; those names are all upper-case -- those aren't
> the names I am
> speaking of.
>
> The names I am speaking of are those in brand-new enumerations where we have
> full control.
>
> As an example:
>
> class FederalHoliday(AutoNumberEnum):
>     NewYear = "First day of the year.", 'absolute', JANUARY, 1
>     MartinLutherKingJr = "Birth of Civil Rights leader.", 'relative',
> JANUARY, MONDAY, 3
>     President = "Birth of George Washington", 'relative', FEBRUARY, MONDAY,
> 3
>     Memorial = "Memory of fallen soldiers", 'relative', MAY, MONDAY, 5
>     Independence = "Declaration of Independence", 'absolute', JULY, 4
>     Labor = "American Labor Movement", 'relative', SEPTEMBER, MONDAY, 1
>     Columbus = "Americas discovered", 'relative', OCTOBER, MONDAY, 2
>     Veterans = "Recognition of Armed Forces service", 'relative', NOVEMBER,
> 11, 1
>     Thanksgiving = "Day of Thanks", 'relative', NOVEMBER, THURSDAY, 4
>     Christmas = "Birth of Jesus Christ", 'absolute', DECEMBER, 25
>
>     def __init__(self, doc, type, month, day, occurance=None):
>         self.__doc__ = doc
>         self.type = type
>         self.month = month
>         self.day = day
>         self.occurance = occurance
>
>     def date(self, year):
>         """
>         returns the observed date of the holiday for `year`
>         """"
>         ...
>
>     @classmethod
>     def next_business_day(cls, date, days=1):
>         """
>         Return the next `days` business day from date.
>         """
>         ...
>     @classmethod
>     def count_business_days(cls, date1, date2):
>         """
>         Return the number of business days between 'date1' and 'date2'.
>         """
>         ...
>     @classmethod
>     def year(cls, year):
>         """
>         Return a list of the actual FederalHoliday dates for `year`.
>         """
>         ...
> Take the name "NewYear":  if it had been a global constant I would have
> named it "NEWYEAR"; if
> it had been a normal class attribute I would have named it "new_year";
> however, being an Enum
> member, it is neither of those things.
>
> <context switch>
> I've written some custom data types as part of my dbf package, and a few of
> them have instances
> that are singletons that are created in the global (okay, module) namespace,
> and for them I
> followed Python's lead in naming singletons:  Python has used Title Case in
> such things as None,
> True, and False, so I followed suit and named mine -- Null, NullDate,
> NullTime, NullDateTime, etc.
> </context switch>
>
> Given my past history with using and creating singleton objects, I followed
> suit when creating
> my own Enum classes.
>
> I was recently queried about my apparent break with PEP 8 for naming Enum
> members, to which I
> replied:
>
>> Considering the strange beast that an Enum is, there is not much precedent
>> for it anywhere.
>>
>> Consider:
>>
>> - Enum is a class
>> -   but it is a container
>> -   and can be iterated over
>> -   and it has a length (which can be zero)
>> -   but it's always True in a boolean sense
>>
>> - Enum members are instances of the Enum class
>> -   but are pre-created
>> -   and new ones cannot be created
>> -   but are available as attributes on the class
>>
>> Given all that I have been using Title case (or CamelCase) to name the
>> members as it helps
>> distinguish an Enum member from an ordinary attribute (which Enum classes
>> can also have).
>
>
> I forgot to include in that reply that I think CamelCase also helps to
> emphasize the special
> singleton nature of Enum members.
>
> My question for the community:  Your thoughts/opinions of my reasoning, and
> if you don't agree
> then which casing choice would you recommend and use, and why?  (Reminder:
> this question does
> not include Enums whose names are replacements for existing constants and so
> the names cannot
> be changed.)
>
> --
> ~Ethan~
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-- 
--Guido van Rossum (python.org/~guido)