On 11/22/2014 06:20 PM, Chris Angelico wrote:
On Sun, Nov 23, 2014 at 11:05 AM, Ron Adam<ron3...@gmail.com> wrote:
>Se we have these...
>
> Tuple Comprehension (...)
> List Comprehension [...]
> Dict Comprehension {...} Colon make's it different from sets.
> Set Comprehension {...}
>
>I don't think there is any other way to create them. And they don't actually
>expand to any python code that is visible to a programmer. They are self
>contained literal expressions for creating these few objects.
Hmmm, there's no such thing as tuple comprehensions.
Just didn't think it through quite well enough. But you are correct, that
would be a generator expression.
One less case to worry about. :-)
lst = [1,2,3,4] # not a comprehension
even = [n*2 for n in lst] # comprehension
>Here is what I think(?) list comps do currently.
>
> lst = [expr for items in itr if cond]
>
>Is the same as.
>
> lst = []
> for x in itr: # StopIteration caught here.
> if cond: # StopIteration bubbles here.
> lst.append(expr) # StopIteration bubbles here.
Pretty much. It's done in a nested function (so x doesn't leak), but
otherwise, yes.
>And it would be changed to this...
>
> def comp_expression():
> for x in itr: # StopIteration caught here.
> if cond:
> list.append(expr)
>
> # StopIteration from cond and expr caught here.
> lst = list(x for x in comp_expression())
That wouldn't quite work, but this would:
Right, the list.append() should be a yield(expr).
def <listcomp>():
ret = []
try:
for x in itr:
if cond:
ret.append(x)
except StopIteration:
pass
return ret
lst = <listcomp>()
(And yes, the name's syntactically illegal, but if you look at a
traceback, that's what is used.)
That's fine too.
The real question is how much breakage would such a change make? That will
probably need a patch in order to test it out.
Cheers,
Ron
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