List difference

Calculates the difference between two iterables, without filtering duplicate values.

• Create a set from b.
• Use a list comprehension on a to only keep values not contained in the previously created set, _b.

def difference(a, b):
  _b = set(b)
  return [item for item in a if item not in _b]

difference([1, 2, 3], [1, 2, 4]) # [3]