On 25 November 2017 at 16:18, Nathaniel Smith <n...@pobox.com> wrote:
> On Fri, Nov 24, 2017 at 9:39 PM, Nick Coghlan <ncogh...@gmail.com> wrote:
>> On 25 November 2017 at 15:27, Nathaniel Smith <n...@pobox.com> wrote:
>>> On Fri, Nov 24, 2017 at 9:04 PM, Nick Coghlan <ncogh...@gmail.com> wrote:
>>>> def example():
>>>> comp1 = yield from [(yield x) for x in ('1st', '2nd')]
>>>> comp2 = yield from [(yield x) for x in ('3rd', '4th')]
>>>> return comp1, comp2
>>>
>>> Isn't this a really confusing way of writing
>>>
>>> def example():
>>> return [(yield '1st'), (yield '2nd')], [(yield '3rd'), (yield '4th')]
>>
>> A real use case
>
> Do you have a real use case? This seems incredibly niche...
That's not how backwards compatibility works - we were suggesting
getting rid of this syntax, because there was no current way to make
it do anything sensible.
It turns out there is a way to make it behave reasonably - you just
need to stick "yield from" in front of it, and it goes back to being
equivalent to the corresponding for loop (the same as the synchronous
version).
>> wouldn't be iterating over hardcoded tuples in the
>> comprehensions, it would be something more like:
>>
>> def example(iterable1, iterable2):
>> comp1 = yield from [(yield x) for x in iterable1]
>> comp2 = yield from [(yield x) for x in iterable2]
>> return comp1, comp2
>
> I submit that this would still be easier to understand if written out like:
>
> def map_iterable_to_yield_values(iterable):
> "Yield the values in iterable, then return a list of the values sent
> back."
> result = []
> for obj in iterable:
> result.append(yield obj)
> return result
>
> def example(iterable1, iterable2):
> values1 = yield from map_iterable_to_yield_values(iterable1)
> values2 = yield from map_iterable_to_yield_values(iterable2)
> return values1, values2
The same can be said for comprehensions in general. Composing them
with coroutines certainly doesn't make either easier to understand,
but I don't think replacing the comprehension with its full imperative
form is particularly helpful in aiding that understanding.
Cheers,
Nick.
--
Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia
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