Thank you Mark....this works too... Btw going slightly off-topic, when i try to run a code like below with around 50 elements (pairs) in l4,python just hangs. Any ideas why this is happening...the data is not that large :(( > > Girish Sahani wrote: >> 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 >> >> The output given is: >> l4 is [[4, 7], [4, 12], [9, 7], [9, 12], [11, 7]] > > It is better to iterate over a copy, e.g. like this: > > 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 > > -- > http://mail.python.org/mailman/listinfo/python-list >
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