Cannot step through asynchronous iterator manually
Kevin Conway
kevinjacobconway at gmail.com
Sat Jan 30 07:35:13 EST 2016
To address the original question, I don't believe a next() equivalent for
async iterables has been added to the standard library yet. Here's an
implementation from one of my projects that I use to manually get the next
value: https://bpaste.net/show/e4bd209fc067. It exposes the same interface
as the synchronous next(). Usage:
await anext(some_async_iterator)
Ultimately, it's a fancy wrapper around the original snippet of 'await
iterator.__anext__()'.
On Sat, Jan 30, 2016 at 6:07 AM Maxime S <maxischmeii at gmail.com> wrote:
> 2016-01-30 11:51 GMT+01:00 Frank Millman <frank at chagford.com>:
>
> > "Chris Angelico" wrote in message
> > news:CAPTjJmoAmVNTCKq7QYaDRNQ67Gcg9TxSXYXCrY==S9Djjna_rA at mail.gmail.com.
> ..
> >
> >
> >> On Sat, Jan 30, 2016 at 7:22 PM, Frank Millman <frank at chagford.com>
> >> wrote:
> >> > We had a recent discussion about the best way to do this, and ChrisA
> >> > suggested the following, which I liked -
> >> >
> >> > cur.execute('SELECT ...)
> >> > try:
> >> > row = next(cur)
> >> > except StopIteration:
> >> > # row does not exist
> >> > else:
> >> > try:
> >> > next_row = next(cur)
> >> > except StopIteration:
> >> > # row does exist
> >> > else:
> >> > # raise exception
> >> >
> >> > Now that I have gone async, I want to do the same with an asynchronous
> >> > iterator.
> >>
> >
> >
> I might be a bit off-topic, but why don't you simply use cursor.rowcount?
>
> For a pure iterator-based solution, I would do something like this (admitly
> a bit cryptic, but iterator-based solutions often are :-) :
>
> async def get_uniqu(ait):
> async for row in ait:
> break
> else:
> raise NotEnoughtRows()
> async for _ in ait:
> raise TooManyRows()
> return row
> --
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