Why Python does *SLICING* the way it does??

[Roy Smith]

In article <3csdegF6p6jpnU1 at individual.net>,
Reinhold Birkenfeld  <reinhold-birkenfeld-nospam at wolke7.net> wrote:
>Roy Smith wrote:
>
>> import types
>> 
>> class slicableDict (dict):
>>     def __getitem__ (self, index):
>>         if type (index) == types.SliceType:
>>             d2 = slicableDict()
>>             for key in self.keys():
>>                 if key >= index.start and key < index.stop:
>>                     d2[key] = self[key]
>>             return d2
>>         else:
>>             return dict.__getitem__ (self, index)
>[...]
>
>> Roy-Smiths-Computer:play$ ./slice.py
>> {'oysters': 4, 'hen': 1, 'porpoises': 5, 'geese': 3, 'ducks': 2}
>> {'hen': 1, 'geese': 3, 'ducks': 2}
>> 
>> I defined d[x:y] as returning a new dictionary which contains those items 
>> from the original whose keys are in the range x <= key < y.  I'm not sure 
>> this is terribly useful but it's a neat demonstration of just how simple 
>> Python makes it to do stuff like this.  I can't imagine how much work it 
>> would be to add a similar functionality to something like C++ multimap.
>
>Other possibility, probably faster when almost all keys in the range are in
>the dictionary:
>
>class sdict(dict):
>    def __getitem__(self, index):
>        if isinstance(index, slice):
>            d = {}
>            for key in xrange(slice.start, slice.stop, slice.step):
>                if key in self:
>                    d[key] = self[key]
>            return d
>        else:
>            return dict.__getitem__(self, index)

The problem with that is it requires the keys to be integers.