Function to remove elements from a list not working (corrected)

[Girish Sahani]

Thanks!It worked....i wasted a lot of time trying to find a bug in my
code...what is wrong in iterating over a list and modifying it?
Doesnt python take the modified list every time the loop starts?
Also in this case, i want to add a condition that if none of the pairs are
in pairList, element = []. How can i do that?
> Le Lundi 12 Juin 2006 10:25, Girish Sahani a écrit :
>> Hi,
>>  I am trying to modify a list of pairs (l4) by removing those
>> pairs which are not present in a third list called pairList.
>>  The following is a simplified part of the routine i have written.
>> However
>> it does not give the correct output. Please help!
>>  Its possible i have made a trivial mistke since i am a newbie.
>>
>> def getl5():
>>     l5 = []
>>     pairList = [[1,2],[3,4],[3,5],[3,6],[9,7],[8,9],[8,7],[7,9],[11,10]]
>>     l4 >
>> [[4,2],[4,7],[4,10],[4,12],[9,2],[9,7],[9,10],[9,12],[11,2],[11,7]]
>> for
>> pair in l4:
>>         if pair not in pairList:
>>             l4.remove(pair)
>>     print "l4 is",l4
>>
>
> You are trying to modify a list while iterating over it, never do that !
>
>> The output given is:
>> l4 is [[4, 7], [4, 12], [9, 7], [9, 12], [11, 7]]
>
> Is this work in your case ?
>
> def getl5():
>     pairList = [[1,2],[3,4],[3,5],[3,6],[9,7],[8,9],[8,7],[7,9],[11,10]]
>     l4 =
> [[4,2],[4,7],[4,10],[4,12],[9,2],[9,7],[9,10],[9,12],[11,2],[11,7]]
>     l4 = [ e for e in l4 if e in pairList ]
>     print "l5 is", l4
>
>
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