[Python-ideas] Where did we go wrong with negative stride?

[Rob Cliffe]

On 27/10/2013 23:34, Rob Cliffe wrote:
>
>> I wonder if it would have been simpler if we had defined a[i:j:-1] as 
>> the reverse of a[i:j]?
>>
> Maybe, I'm not venturing an opinion.
> But if so:  What about negative strides other than -1?  Should 
> a[i:j:-2] always be the reverse of a[i:j:2]?
> My feeling is not, i.e.
> "abcdefghij"[3:8:2] == "dfh"
> but I feel that
> "abcdefghij"[3:8:-2] under this suggestion should be what 
> "abcdefghij"[8:3:-2] is now, i.e. "ige", not "hfd".
> I.e. any non-empty start:stop:stride slice where 0 <= slice < length 
> should always start with the character indexed by "start".
Correction: I meant "where 0 <= start < length".  On reconsideration, 
please ignore this condition.
> Rob Cliffe
>> What are real use cases for negative strides?
>>
>> -- 
>> --Guido van Rossum (python.org/~guido <http://python.org/%7Eguido>)
>>
>>
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