Python：使用带有列表的循环

Question

Say I have a list:

list1=[[1,2,3,4],[5,6,7],[8,9,0,11]]

1. I want to print all the elements of the sublists. How do I write the code for it, using loops?
2. I know how to find the sum of one sublist of a list. Similarly I want to find the sum of all the sublists, basically the sum of list1 .

How do I write the code for that?

Here's the code I tried:

a=[[1,2,3], [1,5,4], [2,4,5]]
i = 0
sum = 0
b=a[1]
while ( i < len(b) ) :
 sum = sum + b[i]
 i = i + 1
print ( sum )

a=[[1,2,3], [1,5,4], [2,4,5]]
i = 0
sum = 0
c=a[2]
while ( i < len(c) ) :
 sum = sum + c[i]
 i = i + 1 
print ( sum )

a=[[1,2,3], [1,5,4], [2,4,5]]
i = 0
sum = 0
d=a[0]
while ( i < len(d) ) :
 sum = sum + d[i]
 i = i + 1
print ( sum )

The output:

10
11
6

I want to find the sum of the given numbers. How do I modify the code? I'm using python3. Loops to be used: while and for .

Answer 1

One problem is that you are declaring a variable called sum that is overriding a Python built-it function by the same name. Once you do that the sum() function won't be available in that instance of Python.

Keep in mind that lists are iterable. So to get each sublist:

list1=[[1,2,3,4],[5,6,7],[8,9,0,11]]

for sublist in list1:
    print(sublist)

[1, 2, 3, 4]
[5, 6, 7]
[8, 9, 0, 11]

You could print out each element individually:

for sublist in list1:
    print(*sublist)

1 2 3 4
5 6 7
8 9 0 11

Or print a newline after each element:

for sublist in list1:
    print(*sublist, sep='\n')

1
2
3
4
5
6
7
8
9
0
11

Since a list is iterable it can be summed using the built-in function sum() . Which one is easier to read?

my_sum = sum(sublist)

OR

my_sum = 0
for number in sublist:
    my_sum += number

You could keep track of each sublists' sum in a variable declared outside of the loop.

sums = 0
for sublist in list1:
    sums += sum(sublist)
print(sums)

56