[Python-ideas] [Python-Dev] Inclusive Range

Terry Reedy tjreedy at udel.edu
Tue Oct 12 19:50:47 CEST 2010


On 10/12/2010 9:52 AM, Antoon Pardon wrote:
> On Fri, Oct 08, 2010 at 05:05:26PM -0400, Terry Reedy wrote:
>> But you really seem to be saying is "What if I sometimes want the
>> end points included and sometimes do not?"  Slice syntax by itself
>> cannot handle all four cases, only one, one was chosen and that was
>> closed-open.
>>
>> If you want flexibility, consider the following:
>>
>> class my_list(list):
>>      def __getitem__(self, key, include_start=True, include_stop=False):

Sorry, the above is a holdover from a previous, experimental version. In 
this version, the extra parameters should be eliminated.
This should be just the expected
          def __getitem__(self, key):

>>          if (isinstance(key,tuple) and len(key)==2 and
>> isinstance(key[0], slice)
>>            and isinstance(key[1],tuple) and len(key[1])==2):
>>              key, (include_start, include_stop) = key

Here I unconditionally set the two include variables from the key.
The default values are ignored and are pure holdover noise.

>>              start,stop,stride = key.indices(len(self))
>>              if include_start == False:
>>                  start += 1
>>              if include_stop == True:
>>                  stop += 1
>>              key = slice(start,stop,stride)
>>              print(key)
>>          return list.__getitem__(self, key)
>>
>> ll = my_list(range(10))
>
> That seems to be an undocumented feature. I didn't know it was possible
> to use extra parameters after key in __getitem__.

They never get passed, and as I said above, should not have been there 
in the version I posted. Sorry for the noise. The actual point is that 
keys can be tuples and tuples can contain a slice and other info.

-- 
Terry Jan Reedy




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