Question

I am trying to find the difference between 2 lists. Basically, I want to know everything that is in list 1 that is not in list 2. The best way to explain it, is with an example:

List1 = [a, a, b, c, d, e]
List2 = [a, b, c, d]

In this example, I would like a function that would return [a, e]

When I use the difference function in python, it will only return “e” and not that there is an additional “a” that is in list 1. When I simply used XOR between the 2 lists, it also only returned “e.”

Answer 1

What you want is really not set subtraction. You can use a Counter:

>>> List1 = ['a', 'a', 'b', 'c', 'd', 'e']
>>> List2 = ['a', 'b', 'c', 'd']
>>> import collections
>>> counter = collections.Counter(List1)
>>> counter.subtract(List2)
>>> list(counter.elements())
['a', 'e']