只求列表中负数的总和

Question

when i used for loop for length of the list I got the correct answer.But when I use for loop for I in range list: I got the correct wrong answer enter image description here the first Image shows when value of i is taken.the second image shoes when for loop is take for length of list.what's the problem here? enter image description here

Answer 1

You can use the filter (to filter negative numbers) and then sum them -

>>> p = [1,2,-3,4,-4,5,6]
>>> sum(filter(lambda x: x < 0, p))
-7

Answer 2

you are indexing the list like this p[1],p[2],p[-3]...

instead you should iterate through the values

p = [1,2,-3,4,-4,5,6]
t = 0
for i in p:
    if i < 0:
        t += i
print(t)

or use range(len(p)):

p = [1,2,-3,4,-4,5,6]
t = 0
for i in range(len(p)):
    if p[i] < 0:
        t += p[i]
print(t)

Answer 3

This is the python code you had in the posted picture.

p = [1,2,-3,4,-4,5,6]
t = 0
for i in p:
   if p[i] < 0:
     t+=p[i]
print(t)

when you use for i in p , we iterate through the list unlike accessing the list values by their index If you print each of the value during the loop

for i in p:
     print(i)
output: 
1
2
-3
4
-4
5
6

Also note that p[-3] indicates 3rd element from tail of the list so the values p[i] in your code are p[1],[2],p[-3],p[4],p[-4],p[5],p[6] equivalent to 2,-3,-4,-4,5,6 giving you a result of ((-3)+(-4)+(-4)) = -11