[Python-ideas] Range and slice syntax

[David Allemang]

That is not what slice.indices does. Per help(slice.indices) -

"S.indices(len) -> (start, stop, stride)

"Assuming a sequence of length len, calculate the start and stop indices,
and the stride length of the extended slice described by S. Out of bounds
indices are clipped in a manner consistent with handling of normal slices.

Essentially, it returns (S.start, len, S.step), with start and stop
adjusted to prevent out-of-bounds indices.

On Tue, Nov 13, 2018, 12:50 PM Vladimir Filipović <hemflit at gmail.com wrote:

> On Mon, Nov 12, 2018 at 4:43 PM Nicholas Harrison
> <nicholasharrison222 at gmail.com> wrote:
> > Only when this is called (implicitly or explicitly) do checks for valid
> objects and bounds occur. From my experience using slices, this is how they
> work in that context too.
>
> On reconsideration, I've found one more argument in favour of (at
> least this aspect of?) the proposal: the slice.indices method, which
> takes a sequence's length and returns an iterable (range) of all
> indices of such a sequence that would be "selected" by the slice. Not
> sure if it's supposed to be documented.
>
> So there is definitely precedent for "though slices in general are
> primarily a syntactic construct and new container-like classes can
> choose any semantics for indexing with them, the semantics
> specifically in the context of sequences have a bit of a privileged
> place in the language with concrete expectations, including strictly
> integer (or None) attributes".
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