On 29/04/13 10:29, Ethan Furman wrote:
On 04/28/2013 04:37 PM, Steven D'Aprano wrote:
On Sun, Apr 28, 2013 at 12:32 PM, Ethan Furman <et...@stoneleaf.us> wrote:
- should an enum item be selectable via __call__ instead of __getitem__
(i.e. Seasons(3) is AUTUMN)
Does anyone know why this is even an issue? Is this pure bike-shedding over the
API, or are there
technical reasons for choosing one over the other?
This is an issue because currently every other type* in Python creates (or
selects ;) its instances via the call syntax:
- bool(1) # True
- int('11') # 11
- str(var) # whatever var had in it, now as a str
I think that's a red herring, because you're comparing the use of the object
constructor with look-up by name.
Seasons[3] should not be considered as constructing an instance from argument
3, but a reverse lookup from raw value to enum value. Hence the use of
__getitem__ rather than __call__.
But one of the latest changes to flufl.enum was to take out the call syntax,
and have only getitem syntax
- Season('AUTUMN') # raises an exception
- Season['AUTUMN'] # Season.AUTUMN
I'm not sure whether flufl.enums support creating additional instances after
the event, but if it did, I would expect that I could say Season('WET') to get
a new instance. I am indifferent to whether or not Season('AUTUMN') should
return the existing AUTUMN enum value.
I think that I lean very slightly to these rules:
- Season(x) constructs new instances. If x is already a Season enum, it returns
x; otherwise if x is a value already used for a Season enum, it raises.
- Season[x] looks up existing instances, and raises if x is not already a
Season value.
but only very slightly.
Not only is this inconsistent with the rest of Python*, but it's going to be a
PITA for data storage/retrieval:
datastore = dbf.Table('storage.dbf', 'event_name C(50); date D; season
SEASON')
def retrieve_record(...):
result = []
for field_type, field_data in record:
result.append(field_type(field_data))
Instead of having field_type be Season, couldn't you make it Season.__getitem__
?
--
Steven
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