On 4 September 2016 at 09:31, Yury Selivanov <yselivanov.ml@gmail.com> wrote:
> With the proposed asynchronous comprehensions syntax, the above code
> becomes as short as::
>
> result = [i async for i in aiter() if i % 2]
After using it a few times in examples, while I'm prepared to accept
the agrammatical nature of "async for" in the statement form (where
the adjective-noun phrase can be read as a kind of compound noun
introducing the whole statement), I think for the comprehension form,
we should aim to put the words in the right grammatical order if we
can:
result = [i for i in async aiter() if i % 2]
Please, no.
It may be totally correct from English grammar POV but brings different syntax from regular async for statement, e.g.
async for row in db.execute(...):
pass
Currently regular comprehensions are pretty similar to `for` loop.
Why async comprehensions should look different from `async for` counterpart?
I think the readability gain from that approach becomes even clearer
with nested loops:
result = [x for aiterable in async outer() for x in async aiterable]
vs the current:
result = [x async for aiterable in outer() async for x in async aiterable]
In the first form, "async" is clearly a pre-qualifier on "outer()" and
"aiterable", indicating they need to be asynchronous iterators rather
than synchronous ones.
By contrast, in the current form, the first "async" reads like a
post-qualifer on "x" (it isn't, it modifies how outer() is handled in
the outer loop), while the second looks like a post-qualifier on
"outer()" (it isn't, it modified how aiterable is handled in the inner
loop)
If that means having to postpone full async comprehensions until
"async" becomes a proper keyword in 3.7 and only adding "await in
comprehensions and generator expressions" support to 3.6, that seems
reasonable to me
Cheers,
Nick.
--
Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia
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