INNER JOIN for sorted lists

inner_join.py

def func(a, b):
    result = []
    x, y = 0, 0
    while (x < len(a)) and (y < len(b)):
        if a[x] > b[y]:
            y += 1
        elif b[y] > a[x]:
            x += 1
        else:
            result.append(a[x])
            x += 1
            y += 1
    return set(result)


a = [1, 2, 3, 4, 5, 7, 8]
b = [3, 4, 5, 6, 7]
func(a, b)  # [3, 4, 5, 7]