On Wed, Jul 6, 2016 at 1:12 PM, Yury Selivanov <[email protected]> wrote:
> This is an interesting idea, but I wonder if instead of using ‘async with’ we
> can actually augment ‘async for’ to do the async finalization.
>
> We can add an __aiter_close__ special method which will return an awaitable.
> In this case, ‘async for’ can always look for that method and call it at the
> end of the iteration. Async generators will implement the method to make
> sure that ‘finally’ is always executed (any number of awaits in ‘finally’ is
> OK; ‘yield’ expressions cannot be used).
I was wondering about that too. This is a fairly substantial change to
how iterators work, though -- currently, it's totally legal and
sometimes very useful to do things like
it = open("...")
# Discard header line (first non-commented line)
for line in it:
if not line.startswith("#"):
break
for body_line in it:
...
or nested for loops like:
for section_header_line in it:
section_info = parse_section_header_line(section_header_line)
if section_info.type == "multi-line":
for body_line in it:
if body_line == "-- end of section --":
break
else:
...
I guess there are a few different options in this design space -- one
could have a dedicated for+with syntax ("async forthwith"?), or an
opt-out utility like
for section_header_line in it:
for body_line in protect_from_close(it):
...
where protect_from_close returns a wrapper object that intercepts
__iter_close__ and ignores it, while passing through other method
calls (__next__/send/throw).
-n
--
Nathaniel J. Smith -- https://vorpus.org
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