[Python-ideas] proper naming of Enum members

Ethan Furman ethan at stoneleaf.us
Mon Jul 18 11:17:42 EDT 2016

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`

     def next_business_day(cls, date, days=1):
         Return the next `days` business day from date.
     def count_business_days(cls, date1, date2):
         Return the number of business days between 'date1' and 'date2'.
     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

> 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.)


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