On 25 Jun 2013 01:08, "alex23" <wuwe...@gmail.com> wrote:
>
> On 25/06/2013 9:35 AM, Fábio Santos wrote:
>>
>> > I'd probably just go with a generator expression to feed the for loop:
>> >
>> > for X in (i for i in ListY if conditionZ):
>> > ....
>>
>> That is nice but it's not lazy. If the condition or the iterables took
>> too long to compute, it would be troublesome.
>
>
> I'm not sure I follow. It's a generator expression, not a list
comprehension, so the condition will be evaluated per item iterated over in
the generator, not across all valid items in ListY at once.
>
for X in (i for i in open('largefile') if is_part_of_header(i)):
The above code would be wasting time on IO and processing. It would load
another line and calculate the condition for every line of the large file
and I just wanted to loop over the few header lines.
itertools.takewhile and fwhile/for..while actually stops the loop when the
condition is not meant, while your example keeps checking the condition
until the end of file, even though it is a generator expression.
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