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Groups > comp.lang.python > #11556

Re: testing if a list contains a sublist

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On 2:59 PM, Nobody wrote:
> On Tue, 16 Aug 2011 01:26:54 +0200, Johannes wrote:
>
>> what is the best way to check if a given list (lets call it l1) is
>> totally contained in a second list (l2)?
> "Best" is subjective. AFAIK, the theoretically-optimal algorithm is
> Boyer-Moore. But that would require a fair amount of code, and Python
> isn't a particularly fast language, so you're likely to get better results
> if you can delegate most of the leg-work to a native library (along the
> lines of Roy's suggestion of using regexps).
>
>
How about using Python's core support for "==" on list objects:

def contains(alist, slist):
    """
    predicate: is *slist* a sublist of *alist*?
    """
    alist_sz = len(alist)
    slist_sz = len(slist)
   
    # special cases
    if slist_sz == 0:       
        return True # empty list *is* a sublist
    elif slist_sz == alist_sz and alist == slist:
        return True
    elif slist_sz > alist_sz:
        return False

    # standard case
    for i in range(alist_sz - slist_sz + 1):
        if slist == alist[i:i+slist_sz]:
            return True
    # fell through "for" loop: no match found
    return False

-John

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Thread

testing if a list contains a sublist Johannes <dajo.mail@web.de> - 2011-08-16 01:26 +0200
  Re: testing if a list contains a sublist Roy Smith <roy@panix.com> - 2011-08-15 20:53 -0400
    Re: testing if a list contains a sublist Laszlo Nagy <gandalf@shopzeus.com> - 2011-08-16 08:51 +0200
      Re: testing if a list contains a sublist alex23 <wuwei23@gmail.com> - 2011-08-16 00:19 -0700
      Re: testing if a list contains a sublist alex23 <wuwei23@gmail.com> - 2011-08-16 00:14 -0700
        Re: testing if a list contains a sublist Laszlo Nagy <gandalf@shopzeus.com> - 2011-08-16 10:00 +0200
        Re: testing if a list contains a sublist Johannes <dajo.mail@web.de> - 2011-08-16 17:26 +0200
      Re: testing if a list contains a sublist ChasBrown <cbrown@cbrownsystems.com> - 2011-08-16 00:24 -0700
    Re: testing if a list contains a sublist Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-08-16 14:23 +0200
      Re: testing if a list contains a sublist Roy Smith <roy@panix.com> - 2011-08-16 08:53 -0400
      Re: testing if a list contains a sublist nn <pruebauno@latinmail.com> - 2011-08-16 07:53 -0700
        Re: testing if a list contains a sublist Laszlo Nagy <gandalf@shopzeus.com> - 2011-08-16 17:17 +0200
          Re: testing if a list contains a sublist Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-08-16 17:39 +0200
        Re: testing if a list contains a sublist Neil Cerutti <neilc@norwich.edu> - 2011-08-16 17:45 +0000
  Re: testing if a list contains a sublist Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-16 12:12 +1000
    Re: testing if a list contains a sublist Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-16 18:19 +1000
  Re: testing if a list contains a sublist ChasBrown <cbrown@cbrownsystems.com> - 2011-08-15 23:14 -0700
  Re: testing if a list contains a sublist ChasBrown <cbrown@cbrownsystems.com> - 2011-08-15 23:13 -0700
  Re: testing if a list contains a sublist ChasBrown <cbrown@cbrownsystems.com> - 2011-08-15 23:14 -0700
    Re: testing if a list contains a sublist Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-16 18:37 +1000
      Re: testing if a list contains a sublist ChasBrown <cbrown@cbrownsystems.com> - 2011-08-16 21:13 -0700
  Re: testing if a list contains a sublist Nobody <nobody@nowhere.com> - 2011-08-16 12:21 +0100
    Re: testing if a list contains a sublist John Posner <jjposner@codicesoftware.com> - 2011-08-16 09:57 -0400
    Re: testing if a list contains a sublist John Posner <jjposner@optimum.net> - 2011-08-16 09:57 -0400
      Re: testing if a list contains a sublist Nobody <nobody@nowhere.com> - 2011-08-17 13:28 +0100
  Re: testing if a list contains a sublist Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-20 12:10 +1000

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