On 06/28/2018 01:11 AM, Steven D'Aprano wrote:
On Wed, 27 Jun 2018 07:48:53 -0700, Ethan Furman wrote:
[Note: there is a similar thread on Python-Ideas, if you would like to
respond there.]
Consider the following Enum definition:
class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3
@property
def lower(self):
return self.name.lower()
def spam(self):
return "I like %s eggs and spam!" % self.lower
class SomeClass:
pass
Which of the above Color attributes are enums, and which aren't?
(In hindsight perhaps you should have called the class EnumType so that
ambiguity would not exist. Then an enum would *always* refer to the
members Color.RED etc, and never to Color itself.)
The problem then is the ambiguity between EnumMeta and EnumType. :/
Answer:
- RED, GREEN, and BLUE are members
- lower and spam() are not
- SomeClass /is/ a member (but not its instances)
Is that by accident or by design?
By design. It is entirely possible to want an enum of types (int, float, str,
etc.).
Question:
Should `SomeClass` be an enum member? When would it be useful to
have an embedded class in an Enum be an enum member?
I honestly cannot think of any reason to nest a class inside of an Enum
class. But if I did, I would probably want it to be just a regular class,
and not an enum member.
If I wanted to nest an Enum class inside an Enum class (but why???) I'd
just inherit from Enum:
class Colour(Enum):
class PrimaryColour(Enum):
RED = 1
GREEN = 2
BLUE = 3
OCTARINE = 8
class SecondaryColour(Enum):
PUCE = 101
MAUVE = 102
BEIGE = 103
TEAL = 104
This really seems to be the sticking point -- what should an Enum of Enums look
like? For example, should the above do
--> list(Colour)
[Colour.PrimaryColour <...>, Colour.SecondaryColour <...>]
or something else?
The only example I have seen so far of nested classes in an Enum is when
folks want to make an Enum of Enums, and the nested Enum should not
itself be an enum member. Since the counter-example already works I
haven't seen any requests for it. ;)
So I'm asking the community: What real-world examples can you offer for
either behavior? Cases where nested classes should be enum members, and
cases where nested classes should not be members.
Is this a trick question?
Heh. Not at all. It is entirely possible to have a real use-case which we
cannot model the way we want in code.
--
~Ethan~
--
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