python remove elements of list from another list WITH MULTIPLE OCCURRENCES of items in both

Question

Related to: Remove all the elements that occur in one list from another

I have listA [1, 1, 3, 5, 5, 5, 7] and listB [1, 2, 5, 5, 7] and I want to subtract occurrences of items from listA. The result should be a new list: [1, 3, 5] Note:

1. 1 had 2 occurrences in listA and once in listB, now it appears 2-1=1 times
2. 2 did not appear in listA, so nothing happens
3. 3 stays with 1 occurrence, as its not in listB
4. 5 occurred 3 times in listA and 2 in listB, so now it occurs 3-2=1 times
5. 7 occurred once in listA and once in listB, so now it will appear 1-1=0 times

Does this make sense?

Answer 1

Here is a non list comprehension version for those new to Python

listA = [1, 1, 3, 5, 5, 5, 7]
listB = [1, 2, 5, 5, 7]
for i in listB:
    if i in listA:
        listA.remove(i)

print listA

Answer 2

In cases like these a list comprehension should always be used:

listA = [1, 1, 3, 5, 5, 5, 7]
listB = [1, 2, 5, 5, 7]

newList = [i for i in listA if i not in listB or listB.remove(i)]

print (newList)

Here are the results:

[1, 3, 5]