Add Enum attributes dynamically

Question

First of, I know Enum in Python are immutable.

I'm trying to get an enum that has each month as an attribute and also other enum values, for example:

class SalesFilter(str, enum.Enum): this_month = 'this_month' last_month = 'last_month' this_year = 'this_year' last_year = 'last_year' jan = 'jan' feb = 'feb' mar = 'mar' apr = 'apr' may = 'may' jun = 'jun' jul = 'jul' aug = 'aug' sep = 'sep' oct = 'oct' nov = 'nov' dec = 'dec'

I wonder if there's a way to generate those months dynamically, I'd like to do something like:

import calendar months = [m.lower() for m in list(calendar.month_abbr)[1:]] class SalesFilter(str, enum.Enum): this_month = 'this_month' last_month = 'last_month' this_year = 'this_year' last_year = 'last_year' for m in months: setattr(SalesFilter, f'{m}', m)

Is there a way to do that? Maybe with metaclasses, but I'm not sure where to start.

You can add those month attributes to the SalesFilter class after defining the basic class — i.e. after and outside the class definition. — martineau
– martineau, Commented Apr 9, 2020 at 21:31
Which of those should be enum members and which should be plain attributes? — Ethan Furman
– Ethan Furman, Commented Apr 9, 2020 at 22:32
@martineau That didn't work, cause the attributes are not Enum values so you cannot compare say: ` x = SalesFilter.jan x == SalesFilter.jan # False cause now x is a string ` — igorgue
– igorgue, Commented Apr 9, 2020 at 22:53

Ethan Furman · Accepted Answer · 2020-12-08 19:06:31Z

The most Pythonic way is using Functional API.

import calendar from enum import Enum # Any iterator of (name, value) pairs. Dictionary is one possible example. months = {} for m in list(calendar.month_abbr)[1:]: months[m.lower()] = m.lower() members = { 'this_month': 'this_month', 'last_month': 'last_month', } # Enum Members, maps Names and Values. members.update(months) # The Logic for mix-in. class SalesLogic: def __init__(self, month): # Several values per member are possible. self.month = month # Functional API, joins Logic with Members. SalesFilter = Enum( 'SalesFilter', members, module='your_module', qualname='your_module.SalesFilter', type=SalesLogic) # Tests. print(type(SalesFilter), type(SalesFilter.apr), SalesFilter.apr.name, SalesFilter.apr.value) # <class 'enum.EnumMeta'> <enum 'SalesFilter'> apr apr x = SalesFilter.jan # Test suggested in comments. if x == SalesFilter.jan and x.value == SalesFilter.jan.value and x.month == 'jan' and x.name == 'jan': print('True') # The 4 tests are True.

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