[Python-3000] my take on "typeclasses"

[Talin]

Ideally, if we get the signature API that's been discussed, then lists 
and tuples and such would have a constraint on their __getitem__ method:

    def __getitem__( self, index:int ):
       ...

Thus, the concept testing code could look to see what types are 
acceptable to the __getitem__ method and make its decision based on that.

Steven Bethard wrote:
> On 5/11/06, Talin <talin at acm.org> wrote:
> 
>>sequence( indexable ):
>>    -- an indexable in which the indexes are successive integers
>>    -- Test: isinstance( index_type, int )
> 
> 
> I think as of Python 2.5, this should be hasattr(index_type, '__index__'), no?
> 
> 
>>mapping( indexable ):
>>    -- an indexable in which the indices are hashable values:
>>    -- Test: hashable( index_type )
>>    -- (Also test for immutable if its feasible)
> 
> 
> This seems all and good, but how do you figure out what "index_type"
> is?  Are you suggesting that "indexables" which want to be identified
> as sequences or mappings need to provide their index type somehow?  If
> so, how?  (By inheriting from an abstract type?)
> 
> STeVe