[Python-Dev] Sets are mappings?

[Nick Coghlan]

Aahz wrote:
> On Tue, Dec 20, 2005, M.-A. Lemburg wrote:
>> Josiah Carlson wrote:
>>> New superclasses for all built-in types (except for string and unicode,
>>> which already subclass from basestring).
>>>
>>> int, float, complex (long) : subclass from basenumber
>>> tuple, list, set : subclass from basesequence
>>> dict : subclass from basemapping
>> set should be under basemapping.
> 
> Are you sure?  Sets are not actually a mapping; they consist only of
> keys.  The Python docs do not include sets under maps, and sets do not
> support some of the standard mapping methods (notably keys()).  Raymond
> Hettinger has also talked about switching to a different internal
> structure for sets.
> 
> (Should this discussion move to c.l.py?  Normally I'd think so, but I
> think it's critical that the core developers agree about this.  It's
> also critical for me to know because I'm writing a book, but that's not
> reason enough to stick with python-dev. ;-)

Close enough to on-topic to stay here, I think. However, I tend to think of 
the taxonomy as a little less flat:

basecontainer (anything with __len__)
   - set
   - basemapping (anything with __getitem__)
     - dict
     - basesequence (anything which understands x[0:0])
         - list
         - tuple
         - string
         - unicode
     - basearray (anything which understands x[0:0,])
         - Numeric.array/scipy.array

Cheers,
Nick.


-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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