On 2016-09-06 9:40 AM, C Anthony Risinger wrote:
On Tue, Sep 6, 2016 at 10:20 AM, Sven R. Kunze <srku...@mail.de
<mailto:srku...@mail.de>> wrote:
On 06.09.2016 03:16, Yury Selivanov wrote:
Whereas the following will produce some sort of async
lists, sets, and dicts?
result = [await fun() async for fun in funcs]
result = {await fun() async for fun in funcs}
result = {fun: await fun() async for fun in funcs}
If so, how do I read values from an async list/set/dict?
Consider "funcs" to be an asynchronous generator/iterable that
produces a sequence of awaitables. The above comprehensions
will await on each awaitable in funcs, producing regular list,
set, and dict.
So, what's the "async" good for then?
Maybe I'm off base here, but my understanding is the `async for`
version would allow for suspension during the actual iteration, ie.
using the __a*__ protocol methods, and not just by awaiting on the
produced item itself.
IOW, `[await ... async for ...]` will suspend at least twice, once
during iteration using the __a*__ protocols and then again awaiting on
the produced item, whereas `[await ... for ...]` will synchronously
produce items and then suspend on them. So to use the async + await
version, your (async) iterator must return awaitables to satisfy the
`async for` part with then produce another awaitable we explicitly
`await` on.
Can someone confirm this understanding? And also that all 4
combinations are possible, each with different meaning:
# Normal comprehension, 100% synchronous and blocking
[... for ...]
# Blocking/sync iterator producing awaitables which suspend before
producing a "normal" value
[await ... for ...]
# Non-blocking/async iterator that suspends before producing "normal"
values
[... async for ...]
# Non-blocking/async iterator that suspends before producing
awaitables which suspend again before producing a "normal" value
[await ... async for ...]
Is this correct?
All correct. I'll update the PEP to better clarify the semantics.
Yury
_______________________________________________
Python-ideas mailing list
Python-ideas@python.org
https://mail.python.org/mailman/listinfo/python-ideas
Code of Conduct: http://python.org/psf/codeofconduct/
