On Tue, 11 Jul 2000, Guido van Rossum wrote:
> [(x,y+z) for x in (1,2,3,4,5,6); for y in "abc" for z in "de"]
>
> For me, the semicolon separates much stronger than the for, so (to me)
> this feels like (applying parentheses to show grouping):
>
> (for x); (for y for z)
When written like the above, i agree that the semicolon separates
more strongly. Perhaps we should rearrange the syntax to make the
semicolon more interior?
This also addresses Greg's poll:
>
> for x in [10, 20, 30]; y in [1, 2]:
> print x+y
[...]
> *Everyone* voted (B).
How about writing this as:
for x; y in [10, 20, 30]; [1, 2]:
print x + y
> And how do you write the other grouping?
As a result, this provides a way to write parallel loops within
list comprehensions, although it might not be very clear until
you're familiar with the way it's written above. At least it's
possible:
[(x, y+z) for x; y in (1, 2, 3, 4, 5, 6); "abc" for z in "de"]
If colons were introduced, would that help keep things clear?
[(x, y+z): for x; y in (1, 2, 3, 4, 5, 6); "abc": for z in "de"]
This would then be directly reminiscent of
for x; y in (1, 2, 3, 4, 5, 6); "abc":
for z in "de":
list.append((x, y+z))
which provides the appropriate meaning.
I don't like extra punctuation, but i'm not sure what else to do
here since "for" alone is a very weak separator.
-- ?!ng
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