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Best way to check that you are at the beginning (the end) of an iterable?

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  Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 14:35 -0700
    Re: Best way to check that you are at the beginning (the end) of an iterable? Cameron Simpson <cs@zip.com.au> - 2011-09-08 08:48 +1000
      Re: Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 16:22 -0700
      Re: Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 16:22 -0700
        Re: Best way to check that you are at the beginning (the end) of an iterable? Cameron Simpson <cs@zip.com.au> - 2011-09-08 10:23 +1000
          Re: Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 17:53 -0700
          Re: Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 17:53 -0700
          Re: Best way to check that you are at the beginning (the end) of an iterable? Chris Torek <nospam@torek.net> - 2011-09-08 14:21 +0000
            Re: Best way to check that you are at the beginning (the end) of an iterable? Cameron Simpson <cs@zip.com.au> - 2011-09-09 08:39 +1000
        Re: Best way to check that you are at the beginning (the end) of an iterable? Tim Chase <python.list@tim.thechases.com> - 2011-09-07 19:01 -0500
          Re: Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 18:08 -0700
          Re: Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 18:08 -0700
        Re: Best way to check that you are at the beginning (the end) of an iterable? Terry Reedy <tjreedy@udel.edu> - 2011-09-07 21:06 -0400
      Re: Best way to check that you are at the beginning (the end) of an iterable? Peter Otten <__peter__@web.de> - 2011-09-09 13:04 +0200
        Re: Best way to check that you are at the beginning (the end) of an iterable? Chris Angelico <rosuav@gmail.com> - 2011-09-09 21:30 +1000
    Re: Best way to check that you are at the beginning (the end) of an iterable? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-09-08 10:24 +1000
      Re: Best way to check that you are at the beginning (the end) of an iterable? Terry Reedy <tjreedy@udel.edu> - 2011-09-07 21:08 -0400
      Re: Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 18:05 -0700
    Re: Best way to check that you are at the beginning (the end) of an iterable? Miki Tebeka <miki.tebeka@gmail.com> - 2011-09-07 17:24 -0700
      Re: Best way to check that you are at the beginning (the end) of an iterable? Laurent <laurent.payot@gmail.com> - 2011-09-07 18:06 -0700
      Re: Best way to check that you are at the beginning (the end) of an iterable? Chris Rebert <clp2@rebertia.com> - 2011-09-07 19:27 -0700

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#12941

On Wed, Sep 7, 2011 at 5:24 PM, Miki Tebeka <miki.tebeka@gmail.com> wrote:
> I guess enumerate is the best way to check for first argument. Note that if someone passes you the iterator as argument you have now way of checking if the consumed items from it.
>
> istail can be implemented using itertools.chain, see https://gist.github.com/1202260

For the archives, if Gist ever goes down:

from itertools import chain

def istail(it):
    '''Check if iterator has one more element. Return True/False and
    iterator.'''
    try:
        i = next(it)
    except StopIteration:
        return False, it

    try:
        j = next(it)
        return False, chain([i, j], it)
    except StopIteration:
        return True, chain([i], it)


t, it = istail(iter([]))
print t, list(it)
t, it = istail(iter([1]))
print t, list(it)
t, it = istail(iter([1, 2]))
print t, list(it)

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