Cannot step through asynchronous iterator manually
Frank Millman
frank at chagford.com
Sat Jan 30 03:22:20 EST 2016
"Ian Kelly" wrote in message
news:CALwzid=sSDSm8hdAN+ORJ54A_jEu9Wc8103iqGKAah8mrj-TXw at mail.gmail.com...
> On Jan 29, 2016 11:04 PM, "Frank Millman" <frank at chagford.com> wrote:
> >
> > Hi all
> >
> > To loop though an iterator one usually uses a higher-level construct
> > such
as a 'for' loop. However, if you want to step through it manually you can
do so with next(iter).
> >
> > I expected the same functionality with the new 'asynchronous iterator'
> > in
Python 3.5, but I cannot find it.
> >
> > I can achieve the desired result by calling 'await aiter.__anext__()',
but this is clunky.
> >
> > Am I missing something?
>
> async for x in aiter:
> pass
>
> Can only be used inside a coroutine, of course.
I know that you can use this to loop through the entire iterator, but I have
a special case.
There are times when I want to execute a SELECT statement, and test for
three possibilities -
- if no rows are returned, the object does not exist
- if one row is returned, the object does exist
- if more that one row is returned, raise an exception
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.
Frank
More information about the Python-list
mailing list