怎么写这里的代码呀？

for I in range 后面该怎么写代码，真的不会，初学者刚学，可能需要比较易懂详细的过程，谢谢您能够愿意花点时间，指点迷津，不胜感激！

for i in range(10):
    lis = ['+', '-', '*', '/']
    first = random.randint(1,20)
    second = random.randint(1,20)
    rule = random.randint(0,3)
    print("题目是:{}{}{}=?".format(first,lis[rule],second))
    answer = eval(input("输入答案："))
    calculate = ""
    if rule == 0:
        calculate = first + second
    elif rule == 1:
        calculate = first - second
    elif rule == 2:
        calculate = first * second
    elif rule == 3:
        calculate = first / second
    if answer == calculate:
        print("答对了")
    else:
        print("答错了")