Difference Between Two Lists with Duplicates in Python

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))

You didn't specify if the order matters. If it does not, you can do this in >= Python 2.7:

l1 = ['a', 'b', 'c', 'b', 'c']
l2 = ['a', 'b', 'c', 'b']

from collections import Counter

c1 = Counter(l1)
c2 = Counter(l2)

diff = c1-c2
print list(diff.elements())