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Date: Tue, 16 Aug 2011 08:51:25 +0200
From: Laszlo Nagy <gandalf@shopzeus.com>
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To: Roy Smith <roy@panix.com>
Subject: Re: testing if a list contains a sublist
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>> hi list,
>> what is the best way to check if a given list (lets call it l1) is
>> totally contained in a second list (l2)?
>>
>> for example:
>> l1 = [1,2], l2 = [1,2,3,4,5] ->  l1 is contained in l2
>> l1 = [1,2,2,], l2 = [1,2,3,4,5] ->  l1 is not contained in l2
>> l1 = [1,2,3], l2 = [1,3,5,7] ->  l1 is not contained in l2
>>
>> my problem is the second example, which makes it impossible to work with
>> sets insteads of lists. But something like set.issubset for lists would
>> be nice.
>>
>> greatz Johannes
Fastest, error-free and simplest solution is to use sets:

 >>> l1 = [1,2]
 >>> l2 = [1,2,3,4,5]
 >>> set(l1)-set(l2)
set([])
 >>> set(l2)-set(l1)
set([3, 4, 5])
 >>>

Although with big lists, this is not very memory efficient. But I must 
tell you, sometimes I use this method for lists with millions of 
integers, and it is very fast and reliable, and memory is not a concern 
for me, at least - some million integers will fit into a few MB of 
memory. Read the docs about set operators  for creating union, symmetric 
difference etc.

Best,

    Laszlo