On Mon, Oct 28, 2013 at 11:49 AM, Tim Peters <tim.peters@gmail.com> wrote:

As a Python implementer, _I_ do, but not as a user. As Guido noted,
under the proposal we have:

s[i:j:k] == s[i:j][::k]

That should (finally?) make it crystal clear that applying the stride
has nothing directly to do with the indices of the selected elements
in the original sequence (`s`).

It's definitely not "finally clear" as it's a change in semantics. What about negative strides other than -1? Which of these is expected?

(A) '012345678'[::-2] == '86420'

'0123456789'[::-2] == '97531'

or:

(B) '012345678'[::-2] == '86420'

'0123456789'[::-2] == '86420'

If (A) I can get the (B) result by writing [::2][::-1] but if (B), I'm forced to write:

s[0 if len(s) % 2 == 1 else 1::2]

or something equally ugly.

--- Bruce

(Also, (A) is the current behavior and switching to (B) would break any existing use of strides < -1.)