Re: Is this PEP-able? fwhile

References	(1 earlier) <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> <CAA=1kxR0sMf2MT-UniaVsEY9pUhc0Tvq+O2aHc6ZBY=Gjt1hOg@mail.gmail.com>
Date	2013-06-25 10:41 +1000
Subject	Re: Is this PEP-able? fwhile
From	wu wei <wuwei23@gmail.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.3791.1372120877.3114.python-list@python.org> (permalink)

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On Tue, Jun 25, 2013 at 10:19 AM, Fábio Santos <fabiosantosart@gmail.com>
 wrote:

> 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.
>
Ah yes, of course, my bad.

It's still possible by raising a StopIteration within the condition
function:

    def is_part_of_header(x):
        if header_condition:
            return True
        else:
            raise StopIteration

But yes, by this point any clarity of the generator expression approach
comes with the cost of more explicit setup of the breaking condition.

Thread

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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