Removing objects from lists

Question

I'm not sure why I get an error saying index out of range when I test this function. Can anyone please help me fix this?

def intersect_lists(L1, L2):
'''(list, list) -> list
Return L1 with items not in L2 removed.
>>> intersect_lists([1, 2, 3, 4, 5, 6], [4, 2, 6])
[2,4,6]
'''
new_list = []

for item in range(len(L1)):
    if L1[item] == L2[item]:
        new_list.append(L1[item])
return new_list

Answer 1

Use list comprehension:

def intersect_lists(L1, L2):
   return [i for i in L1 if i in L2]

However, your specific error is being caused by the fact that you are iterating over the length of L1, which will ultimately lead to an index error because the length of L1 is greater than L2.

Without list comprehension:

def intersect_lists(L1, L2):
   final_list = []
   for i in L1:
      if i in L2:
         final_list.append(i)

   return final_list

Answer 2

Or Boolean And:

list(set(L1) & set(L2))