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Groups > comp.lang.python > #44195
| From | Peter Otten <__peter__@web.de> |
|---|---|
| Subject | Re: Nested iteration? |
| Date | 2013-04-23 18:15 +0200 |
| Organization | None |
| References | <kl6a1f$k2l$1@panix2.panix.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.982.1366733742.3114.python-list@python.org> (permalink) |
Roy Smith wrote:
> In reviewing somebody else's code today, I found the following
> construct (eliding some details):
>
> f = open(filename)
> for line in f:
> if re.search(pattern1, line):
> outer_line = f.next()
> for inner_line in f:
> if re.search(pattern2, inner_line):
> inner_line = f.next()
>
> Somewhat to my surprise, the code worked. I didn't know it was legal
> to do nested iterations over the same iterable (not to mention mixing
> calls to next() with for-loops). Is this guaranteed to work in all
> situations?
That depends on what you mean by "all". A well-behaved iterator like
Python's file object allows mixing of for loops and next(...) calls, but
stupid people who deserve to burn in hell sometimes do
class MyIterable:
def __iter__(self):
reset_internal_counter()
return self
with the consequence that every for loop implicitly resets the iterator's
state.
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Nested iteration? roy@panix.com (Roy Smith) - 2013-04-23 11:40 -0400
Re: Nested iteration? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 17:05 +0100
Re: Nested iteration? Ian Kelly <ian.g.kelly@gmail.com> - 2013-04-23 10:05 -0600
Re: Nested iteration? Peter Otten <__peter__@web.de> - 2013-04-23 18:15 +0200
Re: Nested iteration? Chris Angelico <rosuav@gmail.com> - 2013-04-24 02:21 +1000
Re: Nested iteration? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-23 16:35 +0000
Re: Nested iteration? Ian Kelly <ian.g.kelly@gmail.com> - 2013-04-23 10:30 -0600
Re: Nested iteration? Ian Kelly <ian.g.kelly@gmail.com> - 2013-04-23 10:39 -0600
Re: Nested iteration? Chris Angelico <rosuav@gmail.com> - 2013-04-24 02:42 +1000
Re: Nested iteration? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-23 16:53 +0000
Re: Nested iteration? Terry Jan Reedy <tjreedy@udel.edu> - 2013-04-23 16:49 -0400
Re: Nested iteration? Joshua Landau <joshua.landau.ws@gmail.com> - 2013-04-23 22:14 +0100
Re: Nested iteration? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 22:29 +0100
Re: Nested iteration? Joshua Landau <joshua.landau.ws@gmail.com> - 2013-04-23 22:41 +0100
Re: Nested iteration? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 23:42 +0100
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