I saw this thread so wanted to share a bit of a gotcha we had with enums
internally for anyone trying to handle this stuff
Internally, we have a wrapper around CharField to work with enums (we go
further than just choices and actually have the values be enums), but
there's unfortunately still a good amount of issues in certain use cases
that make it not a great fit to be put into general usage for Django. I do
think it's possible to get things right, but you have to establish certain
rules because the way enums work in Django can sometimes be surprising.
We notably had an issue with translations, and I believe the problem would
occur with other context-sensitive values. Because database operations will
often copy values before using them to save to the database, you're
beholden to (what I believe to be) slightly busted semantics on `copy.copy`
for enums. Probably defining a django-y enum subclass that requires
identity/lookup helpers would make this more usable for the general public
(much like what other people have said).
In [10]: from enum import Enum
In [11]: from django.utils.translation import ugettext_lazy, override
In [12]: class C(Enum):
...: a = ugettext_lazy("Some Word")
In [13]: with override('en'):
...: elt = C.a
...: with override('ja'):
...: copy.copy(elt)
...:
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-13-9c36cbd82121> in <module>
2 elt = C.a
3 with override('ja'):
----> 4 copy.copy(elt)
5
/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/copy.py
in copy(x)
104 if isinstance(rv, str):
105 return x
--> 106 return _reconstruct(x, None, *rv)
107
108
/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/copy.py
in _reconstruct(x, memo, func, args, state, listiter, dictiter, deepcopy)
272 if deep and args:
273 args = (deepcopy(arg, memo) for arg in args)
--> 274 y = func(*args)
275 if deep:
276 memo[id(x)] = y
/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/enum.py
in __call__(cls, value, names, module, qualname, type, start)
289 """
290 if names is None: # simple value lookup
--> 291 return cls.__new__(cls, value)
292 # otherwise, functional API: we're creating a new Enum type
293 return cls._create_(value, names, module=module,
qualname=qualname, type=type, start=start)
/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/enum.py
in __new__(cls, value)
531 return member
532 # still not found -- try _missing_ hook
--> 533 return cls._missing_(value)
534
535 def _generate_next_value_(name, start, count, last_values):
/usr/local/Cellar/python3/3.6.0/Frameworks/Python.framework/Versions/3.6/lib/python3.6/enum.py
in _missing_(cls, value)
544 @classmethod
545 def _missing_(cls, value):
--> 546 raise ValueError("%r is not a valid %s" % (value,
cls.__name__))
547
548 def __repr__(self):
ValueError: 'Japanese Version of Some Word' is not a valid C
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