Calculate the biggest value and the second biggest value

def main(x):
    # x should at least has two elements
    m1, m2 = (x[0], x[1]) if x[0] > x[1] else (x[1], x[0])
    for i in range(2, len(x)):
        if x[i] > m1:
            m2 = m1
            m1 = x[i]
        elif x[i] > m2:
            m2 = x[i]
    return m1, m2


if __name__ == "__main__":
    x = [1, 2, 3, 4, 10, -1]
    y = [10, 9, 3, 1]
    z = [3, 9, 9, 1]
    print(main(x))
    print(main(y))
    print(main(z))

10, 4)
(10, 9)
(9, 9)