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. Are you confusing
comprehension syntax (which has a 'for' loop in it) with
tuple/list/etc display, which doesn't?
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:
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.)
ChrisA
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