On Sat, May 9, 2020 at 8:00 PM Alex Hall <alex.moj...@gmail.com> wrote: > > On Sat, May 9, 2020 at 11:15 AM Ram Rachum <r...@rachum.com> wrote: >> >> Here's an idea I've had. How about instead of this: >> >> itertools.islice(iterable, 7, 20) >> >> We'll just have: >> >> itertools.islice(iterable)[7:20] >> >> >> Advantages: >> 1. More familiar slicing syntax. >> 2. No need to awkwardly use None when you're interested in just specifying >> the end of the slice without specifying the start, i.e. islic(x)[:10] >> instead of islice(x, None, 10) >> 3. Doesn't require breaking backwards compatibility. >> >> >> What do you think? > > > Looking at this, my train of thought was: > > While we're at it, why not allow slicing generators?
Bear in mind that islice takes any iterable, not just a generator. I don't think there's a lot of benefit in adding a bunch of methods to generator objects - aside from iteration, the only functionality they have is coroutine-based. There's no point implementing half of itertools on generators, while still needing to keep itertools itself for all other iterables. > And if we do that, what about regular indexing? > But then, what if I do `gen[3]` followed by `gen[1]`? Is it an error? Does > the generator have to store its past values? Or is `gen[1]` the second item > after `gen[3]`? Or wherever the generator last stopped? > It makes no sense to subscript a generator like that. > Well that's probably why I can't index or slice generators - so that code > doesn't accidentally make a mess trying to treat a transient iterator the way > it does a concrete sequence. A generator says "you can only iterate over me, > don't try anything else". > > Which leads us back to your proposal. `islice(iterable)[7:20]` looks nice, > but it also allows `foo(islice(iterable))` where `foo` can do its own > indexing and that's leading to dangerous territory. > If foo can do its own indexing, it needs to either specify that it takes a Sequence, not just an Iterable, or alternatively it needs to coalesce its argument into a list immediately. If it's documented as taking any iterable, it has to just iterate over it, without subscripting. ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/WADS4DTEVC63P2O2HPEYY5HVXIGWGWMT/ Code of Conduct: http://python.org/psf/codeofconduct/
