Question

I have a piece of code that loads up 2 lists with this code:

with open('blacklists.bls', 'r') as f:
            L = [dnsbls.strip() for dnsbls in f]
with open('ignore.bls', 'r') as f2:
            L2 = [ignbls.stip() for ignbls in f2]

dnsbls contains:

list1
list2
list3

ignbls contains

list2

What I want to do is merge dnsbls and ignbls and then remove any lines that appears more than once and print those with “for”. I was thinking something like:

for combinedlist in L3:
            print combinedlist

Which in the aboe example would print out:

list1
list3

Answer 1

You need to use sets instead of lists:

L3 = list(set(L).difference(L2))

Demonstration:

>>> L=['list1','list2','list3']
>>> L2=['list2']
>>> set(L).difference(L2)
set(['list1', 'list3'])
>>> list(set(L).difference(L2))
['list1', 'list3']

For your purposes you probably don’t have to convert it back to a list again, you can iterate over the resulting set just fine.