Paul Rubin wrote:
> Sybren Stuvel <[EMAIL PROTECTED]> writes:
>> I must say that the for/else construct is a LOT more readable than the
>> rewritten alternatives.
>
> They are all pretty ugly. I prefer the genexp version with a
> hypothetical "is_empty" function:
>
> all_heights = (block.height for block in stack if block.is_marked())
> if is_empty(all_heights):
> raise SomeError("No marked block")
Such a function would have to rebind the generator:
def check_empty(items):
items = iter(items)
try:
first = items.next()
except StopIteration:
return False
return chain([first], items)
all_heights = check_empty(all_heights)
if not all_heights:
raise SomeError
> heights = sum(all_heights)
>
> Python generators don't really work the right way for this though.
You can make it work, but the result tends to be messy:
from itertools import chain
def raiseiter(exc, *args):
raise exc(*args)
yield None # unreachable
def stop():
raise StopIteration
height = sum(block.height for block in chain(stack, raiseiter(SomeError)) if
(not block.is_marked()) or stop())
Peter
--
http://mail.python.org/mailman/listinfo/python-list
