On Sat, May 9, 2020 at 7:10 PM Steven D'Aprano <st...@pearwood.info> wrote:
>
> On Thu, May 07, 2020 at 11:12:28PM +0900, Stephen J. Turnbull wrote:
>
> [...]
> > So of course zip can be said to be used like a class. Its instances
> > are constructed by calling it, the most common (only in practice?)
> > method call is .__iter__, it's invariably called implicitly in a for
> > statement, and usually the instance is ephemeral (ie, discarded when
> > the for statement is exited). But it needn't be. Like any iterator,
> > if it's not exhausted in one iteration context, you can continue it
> > later. Or explicitly call next on it.
>
> Agreed.
>
> In CPython 3.x, zip is a class. In 2.x it was a function returning a
> list. I don't know why it's a class now -- possibly something to do with
> the C implementation? -- but that's not part of the public API, and I
> would not expect that to be a language guarantee. The API is only that
> it returns an iterator, it doesn't have to be any specific class.
>
> If zip were implemented in pure Python, it would probably be a
> generator, something like this:
>
> def zip(a, b):
> while True:
> yield(next(a), next(b))
>
> only better :-)
>
Lemme try.
def zip(*iters):
iters = [iter(i) for i in iters]
try:
while True:
yield tuple(next(i) for i in iters)
except StopIteration:
pass
But ultimately, a generator function is very similar to a class with a
__next__ method. When you call it, you get back a state object that
you can ping for the next value. That's really all that matters. I
think the C implementations tend to be classes but the Python ones
tend to be generators - possibly because a generator function is way
easier to write in Python, but maybe the advantage isn't as strong in
C.
If it's going to have additional constructors, it makes good sense for
it to be a class with classmethods. But again, either way WILL work
just fine.
ChrisA
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