30-seconds-of-code/snippets/difference.md

difference

Returns the difference between two iterables.

Use list comprehension to only keep values not contained in b. Use set to test in in O(1) time.

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]