On Sep 21, 2019, at 01:03, 보성 최 <cbs...@gmail.com> wrote:
>
> How about allowing to create multiple items for each loop in comprehension?
> I'm not sure this grammar is available, though.
>
> for example:
>
> [loop for set]
> s = set()
> for i in range(10):
> s.add(i)
> s.add(i * 10)
> [current comprehension]
> s = {
> x
> for i in range(10)
> for x in (i, i * 10)
> }
Is there a reason it has to be a single comprehension? I think this would be a
lot more readable:
s = {x for x in range(10)} | {x*10 for x in range(10)}
This doesn’t work as well for list comprehensions, or generator expressions,
but it’s still not too horrible with a trivial interleave (flattened-zip)
function:
it = interleave((x for x in range(10)), (x*10 for x in range(10)))
Which brings up another possibility: just build tuples and flatten:
s = set(flatten((x, x*10) for x in range(10))
If you want, you could even make that a single flatten-and-setify function:
def fset(It): return { x for tup in it for x in tup }
s = fset((x, x*10) for x in range(10))
That’s still not quite as readable as your suggestion, but it’s not that bad,
and it’s already available.
> [suggested comprehension]
> s = {
> i, i * 10
> for i in range(10)
> }
I think you could find a way to make this not ambiguous as far as the parser is
concerned, but it might be confusing for human readers.
Remember that you can have a tuple as the yield expression, or you could have i
as one element and a generator expression as the second, and possibly other
things. I think all such other things would require an extra set of parens in
every possible case, so the parser doesn’t have to do any extra look ahead or
anything, but I think most humans don’t internalize the exact rules for when
tuples do and don’t require parens, etc.
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