为什么我的代码不会对列表中负数的值求和？

Question

given_list3 = [7, 5, 4, 4, 3, 1, -2, -3, -5, -7]
total7 = 0
i = 0
while i <= len(given_list3) and given_list3[i] <= 0:
    total7 += givenlist3[i]
    i += 1
print(total7)

The code is producing a result of 0, and I want to to result in: -2 + -3 + -5 + -7 = -17

Answer 1

You can use comprehension:

given_list3 = [7, 5, 4, 4, 3, 1, -2, -3, -5, -7]
output = sum(x for x in given_list3 if x < 0)
print(output) # -17

In your current code, you are exiting the while loop even before the first iteration, because the second condition given_list3[i] <= 0 is false (since the first item 7 is greater than 0 ). If you want a working version, try the following. (Also you need to use i < len(...) , not i <= len(...) .)

given_list3 = [7, 5, 4, 4, 3, 1, -2, -3, -5, -7]
total7 = 0
i = 0
while i < len(given_list3):
    if given_list3[i] <= 0:
        total7 += given_list3[i]
    i += 1
print(total7) # -17

Answer 2

A while loop stops when the condition is false. So your loop stops when it gets to the first positive value. Since the first element of the list is positive, the loop doesn't do anything.

The negative condition should be if inside the loop.

Also, list indexes go to len(list)-1 , so the length condition should be < , not <= .

while i < len(given_list3):
    if given_list3[i] <= 0:
        total7 += given_list3[i]
    i += 1

You should get out of the habit of looping over list indexes. Use for-in :

for item in given_list3:
    if item <= 0:
        total7 += item

Answer 3

You never iterate through your while loop. This is the first iteration of your while loop when i = 0:

while 0 <= len(given_list3) and given_list3[0] <= 0:

0 <= len(given_list3) - true; 0 is less than 10 given_list3[0] <= 0 - false; given_list3[0] = 7 and 7 is not less than or equal to 0.