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| References | <8D03F2B8CF0E7BE-1864-1796B@webmail-m103.sysops.aol.com> <mailman.3760.1372104769.3114.python-list@python.org> <kqajj8$54h$1@dont-email.me> <mailman.3788.1372116912.3114.python-list@python.org> <kqam8g$f7n$1@dont-email.me> |
|---|---|
| Date | 2013-06-25 01:19 +0100 |
| Subject | Re: Is this PEP-able? fwhile |
| From | Fábio Santos <fabiosantosart@gmail.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.3790.1372120016.3114.python-list@python.org> (permalink) |
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On 25 Jun 2013 01:08, "alex23" <wuwei23@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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Re: Is this PEP-able? fwhile Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-24 14:12 -0600
Re: Is this PEP-able? fwhile alex23 <wuwei23@gmail.com> - 2013-06-25 09:14 +1000
Re: Is this PEP-able? fwhile Fábio Santos <fabiosantosart@gmail.com> - 2013-06-25 00:35 +0100
Re: Is this PEP-able? fwhile alex23 <wuwei23@gmail.com> - 2013-06-25 10:00 +1000
Re: Is this PEP-able? fwhile Fábio Santos <fabiosantosart@gmail.com> - 2013-06-25 01:19 +0100
Re: Is this PEP-able? fwhile wu wei <wuwei23@gmail.com> - 2013-06-25 10:41 +1000
Re: Is this PEP-able? fwhile Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-24 22:50 -0600
Re: Is this PEP-able? fwhile rusi <rustompmody@gmail.com> - 2013-06-24 23:04 -0700
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