On Wed, Oct 7, 2020 at 4:53 AM Christopher Barker <python...@gmail.com> wrote:
>
> On Tue, Oct 6, 2020 at 10:28 AM Alex Hall <alex.moj...@gmail.com> wrote:
>>
>>
>> if you want to iterate through items N to the end, then how do you do that
>> without either iterating through the first N and throwing them away, or
>> making a slice, which copies the rest of the sequence?
>>
>> ```python
>> for i in range(start, stop):
>> x = lst[i]
>> process(x)
>> ```
>
>
> well yes, of course. but it's kind of a principle in Python that you don't
> use indices to iterate through a sequence :-)
>
> And I still like the sequence view idea, because then the creating of the
> "subview" could be done outside the iteration code, which would not have to
> know that it was working with a sequence, rather than any arbitrary iterable.
>
Slices returning views would be elegant, but backward incompatible, so
it might have to be something like lst.view[start:stop] to create a
view. I'm not a fan of an "advance this iterator" feature (it'd need a
dunder on the iterator to make it possible, and I don't see a lot of
use for it), but perhaps some iterators could themselves support
slicing. That would be completely backward compatible, since currently
none of the iterators concerned have any support for indexing. If you
had that, you could build your own advance() or consume() function,
something like:
def advance(it, n):
try:
return it[n:]
except TypeError:
return itertools.islice(it, n, None)
Still unconvinced of its value, but a good use-case would sway me, and
the C implementation for list_iterator wouldn't be too hard (it'd
construct a new list_iterator with the same underlying list and an
incremented index).
ChrisA
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