On 31 January 2013 12:27, Tim Delaney <timothy.c.delaney@gmail.com> wrote:
On 31 January 2013 08:32, Terry Reedy <tjreedy@udel.edu> wrote:
On 1/30/2013 10:30 AM, Michael Foord wrote:
On 30 January 2013 15:22, Michael Foord
With a Python 3 metaclass that provides default values for *looked
up* entries you could have this:
class Color(Enum): RED, WHITE, BLUE
The lookup would create the member - with the appropriate value.
class values(dict): def __init__(self): self.value = 0 def __getitem__(self, key):
So RED, WHITE, BLUE are 1, 2, 3; not 0, 1, 2 as I and many readers might expect. That aside (which can be fixed), this is very nice.
Here is a version that I think creates an enum with most of the features of traditional and modern enums.
- Enum values are subclasses of int;
- Only need to declare the enum key name;
- Starts at zero by default;
- Can change the start value;
- Can have discontiguous values (e.g. 0, 1, 5, 6);
- Can have other types of class attributes;
- Ensures that there is a 1:1 mapping between key:value (throws an exception if either of these is violated;
- Able to obtain the keys, values and items as per the mapping interface (sorted by value);
- Lookup an enum by key or value;
One thing to note is that *any* class attribute assigned a value which implements __index__ will be considered an enum value assignment.
Forgot about making it iterable - an easy-to-ad feature. Obviously it would iterate over the EnumValue instancess. Thought I'd better make it explicit as well that this was based on Michael Foords brilliant work. Tim Delaney