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

[Ron Adam]

On 10/28/2013 04:31 PM, Tim Peters wrote:
> That's not what the proposal said, but it's a reasonable alternative.
> Maybe that's better because it's "more compatible" with what happens
> today.  The hangup for me is that I have no use cases for negative
> strides other than -1, so have no real basis for picking one over the
> other.  OTOH, since I_don't_  have any use cases, I don't care either
> what happens then;-)
>
>> >s[i:j:-k] == s[i:j:-1][::k]
> That's a nice form of symmetry too.  Sold;-)

+1  Looks good to me.


We could add a new_slice object without any problems now.  You just need to 
be explicit when using it.

(This works now)

 >>> "abcdefg"[slice(1,5,1)]
'bcde'


And this could work and not cause any compatibility issues.

     "abcdefg"[new_slice(1, 5, -2)]
     "ec"


It would offer an alternative for those who need or want it now and help 
with the change over when/if the time comes.

We also need to remember that slicing is also used for inserting things.

 >>> a = list("python")
 >>> b = list("PYTHON")
 >>> a[::2] = b[::2]
 >>> a
['P', 'y', 'T', 'h', 'O', 'n']


Cheers,
     Ron