Difference Between Two Lists with Duplicates in Python

Question

I have two lists that contain many of the same items, including duplicate items. I want to check which items in the first list are not in the second list. For example, I mig

Answer 1

Create Counters for both lists, then subtract one from the other.

from collections import Counter

a = [1,2,3,1,2]
b = [1,2,3,1]

c = Counter(a)
c.subtract(Counter(b))