python判断素数

def slowsnail(num):
    count = num // 2
    while count > 1:
        if num % count == 0:
            print('%d最大的约数是%d' % (num, count))
            break
        count -= 1
    else:
        print('%d是素数！' % num)


num = int(input('请输入一个数：'))
slowsnail(num)