On Sat, May 9, 2020 at 11:15 AM Ram Rachum <ram@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?
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?
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.