Python｜列表的逆向遍历

1···list1 = [ 'apple', 'banana', 'grape', 'peach', 'orange', 'pear' ]，按照样例输出格式逆向将列表中的元素逐一遍历输出

list1 = [ 'apple', 'banana', 'grape', 'peach', 'orange', 'pear' ]
for i in range(len(list1)-1,-1,-1):
    print(list1[i],end=",")

 

2···列表如下：list1 = [ [1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 20] ]，按3行4列形式打印输出如下的二维列表（每个元素靠左对齐，占3列 

list1 = [ [1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 20] ]

for i in range(len(list1)):
    for j in range(len(list1[0])):
        print("{:<3d}".format(list1[i][j]),end="")
    print()

 

3···a=[3,6,9]，键盘输入列表b，计算a中元素和b中对应元素乘积的累加和。（要求列表b为[1,2,3]，累加和是：3*1+6*2+9*3=42，屏幕输出计算结果42即可） 

a  =[3,6,9]
b = eval(input())
s=0
for i in range(3):
    s=s+a[i]*b[i]
print(s)