def mul(x= 5, *nums):

    if len(nums) == 0:

        return x

    for i in nums:

        x *= i

    return x

print('mul(5) =', mul(5))

print('mul(5, 6) =', mul(5, 6))

print('mul(5, 6, 7) =', mul(5, 6, 7))

print('mul(5, 6, 7, 9) =', mul(5, 6, 7, 9))

if mul(5) != 5:

    print('测试失败!')

elif mul(5, 6) != 30:

    print('测试失败!')

elif mul(5, 6, 7) != 210:

    print('测试失败!')

elif mul(5, 6, 7, 9) != 1890:

    print('测试失败!')

else:

    try:

        mul()

        print('测试失败!')

    except TypeError:

        print('测试成功!')